PENULIS BATUSANGKAR (SMAN 3 BATUSANGKAR)

Jumat, 12 September 2008

Yellowstone National Park

Picture a place where you can see smelly gray mud bubbling up from the ground and steaming hot water shooting out of rocks. In the distance, high waterfalls tumble through colorful canyons.

It may sound like make-believe, but you can find all these things in Yellowstone National Park. Yellowstone is in the United States and it’s the oldest national park in the world.

WHAT’S A NATIONAL PARK?

A national park is land set aside by the government in order to protect it. Yellowstone was made a national park in 1872. People realized it was a very special place that should be preserved.

National parks are also created so people can enjoy nature. In Yellowstone, you can do things such as camp, hike in the woods, ride horses, and go fishing.

WHERE IS YELLOWSTONE?

Yellowstone sits in the Rocky Mountains. Most of Yellowstone is in the northwest corner of Wyoming. But parts are in Idaho and Montana, too.

WHAT MAKES YELLOWSTONE SO SPECIAL?

The ground beneath Yellowstone contains a large amount of hot melted rock, called magma. The magma heats water in the ground. The steaming water pushes to get to the surface, much like steam whistling from a boiling teapot.

Sometimes the heated water forms a geyser. A geyser is a place where hot water spouts up from underground. There are more than 300 geysers in Yellowstone, some big and some small. Other times the hot water seeps from the ground as a hot spring. There are even more hot springs in Yellowstone than geysers.

If you explore Yellowstone, you may also see steam vents, which is where steam and other gases puff out of the ground. You can even find “paint pots” in the park. Paint pots are holes full of bubbling mud that is thick like paint. Sometimes the pots smell like rotten eggs or burnt matches.

OLD FAITHFUL

The most famous geyser in the world is Old Faithful and it’s in Yellowstone. It blows its top about every 30 to 90 minutes. It shoots thousands of gallons of hot water high into the air. Visiting Old Faithful is a highlight of any trip to Yellowstone.

OTHER NATURAL WONDERS

What else can you see in Yellowstone? How about Yellowstone’s own Grand Canyon? It has two big waterfalls and high cliffs of yellow, red, and orange rock.

There’s a forest of stone trees in Yellowstone that is millions of years old. The trees were once buried by ash from a volcano and were gradually turned to stone. There are also beautiful lakes, rivers, and mountains to see and enjoy.

Yellowstone is rich with wildlife. Hundreds of kinds of birds live in the park, including bald eagles, blue herons, and white pelicans. Yellowstone is home to many large animals. Visitors may see black bears, grizzly bears, moose, bighorn sheep, deer, cougars, herds of elk, and bison (buffalo).

Protecting animals in the wild is one of the most important tasks of the park. In fact, the creation of Yellowstone helped save bison from being hunted to extinction in the late 1800s.

WELCOME BACK WOLVES

Yellowstone was once home to thousands of gray wolves. But people thought they were dangerous and killed them off. The last wolf in the park was killed in the 1930s.

In 1995 and 1996, biologists brought about 30 wolves from Canada and released them inside Yellowstone. Wolf packs soon formed. New pups are born in the park every year. There are now more than 200 wolves in and around the park! Today, seeing a wolf is one of Yellowstone’s big attractions.

Rocky Mountains

They are home to jagged peaks, sparkling lakes, and rushing rivers. They offer some of the best skiing and most spectacular scenery in North America. They are North America’s longest mountain chain. They are the great Rocky Mountains.

MILES AND MILES OF MOUNTAINS

The Rocky Mountains are in western North America. They rise dramatically from the Great Plains of central Canada and the United States.

The mountains run from northeastern British Columbia to central New Mexico. That adds up to a distance of about 2,000 miles (about 3,200 kilometers).

The Rocky Mountains have four main sections: the Southern, Central, Northern, and Canadian.

SOUTHERN ROCKIES

The Southern Rockies run from central New Mexico through Colorado to southern Wyoming. This is the broadest part of the range. Here, the mountains reach a width of more than 300 miles (480 kilometers).

The Southern Rockies are home to the chain’s highest peaks. More than 50 mountains in Colorado are more than 14,000 feet (4,300 meters) tall. The tallest is Mount Elbert in central Colorado. It rises to 14,433 feet (4,399 meters).

CENTRAL ROCKIES

The Central Rockies rise in northeastern Utah, western Wyoming, eastern Idaho, and southern Montana. Some world-famous parks are here, including Yellowstone National Park and Grand Teton National Park.

NORTHERN ROCKIES

The Northern Rockies cross northern Idaho, western Montana, and northeastern Washington. Glacier National Park is found in the northern Rockies.

CANADIAN ROCKIES

The Canadian Rockies are a relatively narrow belt of mountains in southwestern Alberta and eastern British Columbia. The mountains here are only about 50 miles (80 kilometers) wide in places.

There are many icy peaks, massive glaciers, and turbulent rivers in the Canadian Rockies. The slopes tend to be very steep. The region is known for its magnificent scenery.

THE CONTINENTAL DIVIDE

The Rocky Mountains form part of the Continental Divide. Rivers on the western side of the divide flow west to the Pacific Ocean. Rivers on the eastern side of the divide flow east, to Hudson Bay in the north and the Gulf of Mexico in the south.

LIFE IN THE ROCKIES

Summers in the Rockies are short and cool. Winters are long and cold. Many peaks are capped in snow and ice all year long. Wild animals such as antelope, moose, grizzly bears, and mountain lions thrive in the Rockies.

Many people vacation in the Rocky Mountains. In the summer, visitors come to hike, bicycle, or camp. In the winter, many come to ski, snowboard, or snowmobile.

Disneyland and Disney World

Have you met Mickey Mouse or Minnie Mouse? If you have, you’ve probably been to Disneyland or Disney World. These popular theme parks are based on Walt Disney cartoons and motion pictures. You can see Mickey, Minnie, and all the other cartoon residents of these fantasy kingdoms. You can enjoy rides and other attractions, too.

WHAT IS DISNEYLAND LIKE?

Disneyland was the first Disney theme park. It opened in Anaheim, California, in 1955. Disneyland was created by cartoonist Walt Disney. He invented Mickey Mouse, Donald Duck, Goofy, and many other cartoon characters. Walt Disney died in 1966. The company he founded runs the theme parks.

Walt Disney wanted rides at Disneyland to be like stepping into a fantasy world. You can ride around and around in a giant teacup at the Mad Tea Party. It’s borrowed from the Mad Hatter’s party in Alice in Wonderland. You can fly through the air on the Dumbo the Flying Elephant ride. You can glide in a boat and watch pirates fight in the Pirates of the Caribbean attraction. You can ride an old-time train around the park. You can stroll down Main Street, an old-time town display. You can also stay at Disneyland hotels.

WHAT IS DISNEY WORLD LIKE?

Disney World opened near Orlando, Florida, in 1971. It has four different theme parks. The Magic Kingdom came first. It has many of the same rides and attractions as Disneyland. The spires of Cinderella’s castle soar above the Magic Kingdom.

You and your family might enjoy Epcot, a Disney World theme park that features countries and cultures of the world. It also has some science exhibits. At Epcot, you can “visit” such countries as China, England, France, Morocco, Japan, and Mexico. You can eat the foods of these countries or buy gifts made there.

The other two theme parks at Disney World are Disney-MGM Studios and Disney’s Animal Kingdom Park. At Disney-MGM Studios, you can enjoy rides and shows based on Hollywood movies. At Animal Kingdom, you can take a safari ride to see elephants, giraffes, hippos, rhinos, and lions. There are also two Disney water parks: Blizzard Beach and Typhoon Lagoon. Both parks have water slides and other water adventures.

You can stay at one of almost 20 theme resorts owned by the Walt Disney Company near Orlando. The Grand Floridian is a very fancy resort. The Caribbean Beach resort looks like a tropical beach. You can even stay at a Disney campground. Boats, buses, and a monorail connect all the Disney World theme parks.

Niagara Falls

Other waterfalls are higher than Niagara Falls, but Niagara Falls is one of the most famous. Why? Because the great beauty and immense size of Niagara Falls make it one of North America’s most spectacular natural wonders!

WHERE IS NIAGARA FALLS?

Niagara Falls is part of the Niagara River. The Niagara is a short river, just 35 miles (56 kilometers) long. It connects Lake Erie and Lake Ontario in eastern North America. East of the river is the United States. West of the river is Canada. About halfway between the two lakes, a sharp drop in the river makes Niagara Falls.

TWO GIANT WATERFALLS

Niagara Falls is actually two giant waterfalls and one smaller one. Goat Island, in New York state, lies between the two main falls.

One big waterfall, called American Falls, is on the U.S. side of the river. American Falls has a fairly straight edge. The waterfall is 1,075 feet (328 meters) wide and 182 feet (55 meters) high. A small part of American Falls, located near Goat Island, is called Bridal Veil Falls.

The biggest of the two giant waterfalls is in Canada and is known as the Canadian Falls. It’s also called the Horseshoe Falls because of its horseshoe shape. The curved edge of the Canadian Falls measures 2,200 feet (670 meters) wide, and the water drops 187 feet (57 meters). The Canadian Falls carries nine times more water than the American Falls!

VISITING NIAGARA FALLS

Niagara Falls is a popular tourist attraction. Millions of people come each year to watch the spectacular waterfalls. You can take a boat trip to see the falls from below. You can also watch from observation decks above or beside the falls. You can even enter the Cave of the Winds, a path that takes you to the base of Bridal Veil Falls. Visitors must wear bright-yellow rain jackets to stay dry!

Niagara Falls makes an enormous, ground-shaking roar and a huge cloud of water mist. Rainbows shine through the mist. At night, the falls are lit with colored lights, creating a brilliant display!

Great Lakes

The Great Lakes are so large, you could easily see them if you stood on the Moon! They’re the world’s largest group of freshwater lakes, and they’re found in North America.

Five lakes make up the Great Lakes. They are Lake Superior, Lake Michigan, Lake Huron, Lake Erie, and Lake Ontario.

WHERE ARE THE GREAT LAKES?

The Great Lakes are located in the eastern half of North America along the United States-Canadian border. The lakes are a part of both countries and are shared by both. Only Lake Michigan lies entirely within the United States.

Eight American states border the lakes to the south. They are New York, Pennsylvania, Ohio, Indiana, Michigan, Illinois, Minnesota, and Wisconsin. The big Canadian province of Ontario is on the north side of the lakes.

Four of North America’s largest cities are located on the edge of the Great Lakes. They are Chicago, Detroit, Toronto, and Cleveland.

HOW DID THE GREAT LAKES FORM?

Huge glaciers moving over the land dug out the Great Lakes. The glaciers melted away about 10,000 years ago. Before the glaciers came, the area now covered by the lakes was made up of plains, broad valleys, and rivers.

HOW BIG ARE THEY?

The five lakes cover an area 94,250 square miles (244,100 square kilometers). That makes them larger than the states of Indiana and Illinois combined! All together, the lakes hold about 20 percent of all the fresh water on the Earth’s surface.

Lake Superior is the biggest of the Great Lakes. In fact, it’s the world’s largest body of fresh water. It is 350 miles (560 kilometers) long and it reaches a depth of 1,332 feet (406 meters). Lake Ontario is the smallest of the Great Lakes.

SHIPPING AND RECREATION ON THE GREAT LAKES

The five Great Lakes are linked by rivers and canals. These allow ships to sail from lake to lake. The St. Lawrence River provides an outlet for large vessels to the Atlantic Ocean. The Great Lakes, together with the St. Lawrence River, form one of the most important inland waterway systems in the world.

Today, the Great Lakes are among the world’s busiest shipping routes. Farms, factories, and businesses ship iron ore, coal, grain, steel, automobiles, and other goods across the lakes and beyond.

The Great Lakes are also popular for recreation. There are thousands of homes and cabins on the shores. Millions of people flock to the lakes in the summer to water-ski, sail, fish, and swim.

Amazon River

A dense, green forest lines the riverbanks. Monkeys chatter in the trees. Off to the side, a big crocodile sticks its eyes and nose out of the water. This is what a boat trip on the Amazon River can be like. Be careful not to fall overboard! Fish called piranhas may be swimming near the boat. A group of piranhas can gobble up a large animal in minutes.

THE MIGHTY AMAZON

The Amazon is a long river in South America. The river starts in snow and tiny streams, high in the Andes Mountains in Peru. It flows east through Brazil. After 4,000 miles (6,400 kilometers), the Amazon empties into the Atlantic Ocean.

Along its route, hundreds of streams and smaller rivers empty into the Amazon. As a result, the Amazon carries more water than any other river in the world. Although the Amazon is the largest river in the world, it is not the longest. Only the Nile River in Africa is longer than the Amazon.

The Amazon changes size through the year. It is biggest from January to June, when heavy rains fall in Brazil. During the rainy season, the river is more than 50 miles (80 kilometers) wide in some places.

The Amazon dumps several million tons of mud, sand, and other sediment in the Atlantic Ocean every day. Much of this sediment has washed down from the Andes Mountains. It turns the Amazon a muddy yellowish color. The sediment changes the color of the Atlantic for about 200 miles (about 320 kilometers) from the mouth of the Amazon.

WHAT ANIMALS LIVE IN THE AMAZON?

The Amazon is home to many interesting animals. The piranha is an Amazon fish with a bad reputation. One species (kind) of piranha has powerful jaws and sharp teeth that can tear flesh from bones. However, most piranhas eat plants. Stingrays and electric eels live in the Amazon, too. Stingrays have poisonous stingers on their tails. Snakelike electric eels use their electricity to stun prey.

Giant otters, river dolphins, and manatees are among the mammals found in the Amazon. Crocodiles called caimans and giant turtles also live in the river.

THE AMAZON RAIN FOREST

A vast tropical rain forest lies next to the Amazon River in Brazil and neighboring countries. More than seven times the size of Texas, it is the largest rain forest in the world.

The Amazon rain forest is home to colorful scarlet macaws, stealthy jaguars, noisy howler monkeys, bloodsucking vampire bats, three-toed sloths, long-nosed tapirs, and powerful anaconda snakes. Many useful plants grow in the Amazon rain forest. They provide food, building materials, rubber, medicines, and other products.

Atlantic Ocean

If you look at a map of the world, you’ll see a body of water that runs the length of Earth in a huge, S-shaped curve. That’s the Atlantic Ocean, the world’s second biggest ocean. Only the Pacific Ocean is larger.

The World’s Oceans
Ocean	square miles	square kilometers

Pacific Ocean	63,980,000	165,700,000
Atlantic Ocean	31,810,000	82,400,000
Indian Ocean	28,360,000	73,440,000
Arctic Ocean	5,430,000	14,060,000

WHERE IS THE ATLANTIC OCEAN?

The Atlantic Ocean separates North and South America from Europe and Africa. In the north, it reaches past Greenland to the Arctic Ocean. In the south, it touches the continent of Antarctica.

The middle of the Atlantic is a vast expanse of water. Around its edges, it opens to a number of seas. In the east, you can sail from the Atlantic into the Mediterranean Sea through a tiny opening called the Strait of Gibraltar. In the west, you can sail into the Caribbean Sea and the Gulf of Mexico.

Geographers divide the Atlantic Ocean into two parts at the equator, the imaginary line that circles Earth around its middle. These parts are the North Atlantic Ocean and the South Atlantic Ocean.

HOW DID THE ATLANTIC FORM?

The continents on either side of the Atlantic Ocean look like puzzle pieces that could slide together. Why is this?

Millions years ago, most of the world’s land was in two huge continents, called Laurasia and Gondwanaland. The two continents then began to spilt apart, east to west. Water filled the gap between them, creating the Atlantic Ocean. The ocean is still growing larger today.

MID-ATLANTIC RIDGE

The rift between the continents is still down there. It runs along an underwater mountain range called the Mid-Atlantic Ridge. The Mid-Atlantic Ridge is the world’s longest mountain system. It extends 9,300 miles (15,000 kilometers) along the ocean floor, north to south. It’s loaded with live volcanoes.

A deep valley extends along the crest of the ridge. This is where the seafloor is spreading apart. Where the seafloor spreads, molten (melted) rock rises from beneath Earth’s surface. The rock cools and becomes the ocean’s new floor. The Atlantic Ocean widens a little over 1 inch (3 centimeters) each year.

FEW ISLANDS

Compared to the Pacific Ocean, the Atlantic Ocean has very few islands. The largest islands and island groups border the continents. They include the island of Newfoundland and the Caribbean Islands off North America. In the far north, a part of Greenland, the world’s largest island, reaches into the North Atlantic Ocean. The British Isles make up the largest island group off Europe.

Most islands in the middle of the Atlantic are volcanoes. Iceland, the Azores, Saint Paul’s Rocks, Ascension, and the Tristan da Cunha group all were formed by volcanic action along the Mid-Atlantic Ridge.

OCEAN CURRENTS

The surface waters of the Atlantic travel in great circle-shaped currents. They move like rivers within the ocean. Currents in the North Atlantic move clockwise. Those in the South Atlantic move the opposite way.

North of the equator, the Gulf Stream current flows south past Europe. It curves west near the equator and then flows north along North America. Near Canada, it curves east again. The current carries warm water north from the Gulf of Mexico. The Brazil Current is a similar type of current south of the equator.

BUSY SEA LANES

More ships cross the North Atlantic than any other ocean. That’s because lots of things are made on both sides of the ocean. Countries in Europe trade heavily with those in North America. Much of this trade is done by ship.

Mississippi River

The Mississippi River is the most important river in North America. It provided a major highway for early explorers of North America. Many cities grew up along it. Furs and farm goods traveled from these settlements down the river to markets. Today, more freight travels on the Mississippi than on any other waterway within the continent.

FATHER OF WATERS

The Mississippi is known as the Father of Waters. It splits the United States from north to south in the nation’s heartland. The Mississippi gathers waters from rivers that lie between the Appalachian Mountains in the East and the Rocky Mountains in the West.

The Ohio River flows into the Mississippi at Cairo, Illinois. The Missouri River empties into it near St. Louis, Missouri. The Illinois and Arkansas are other major rivers that flow into the Mississippi.

LARGEST BUT NOT LONGEST

The Mississippi is the largest river in North America. This means that it carries more water than any other North American river. But the Mississippi is not the longest river. That honor goes to the Missouri. The Missouri is 200 miles (320 kilometers) longer.

The Mississippi starts at Lake Itasca in northern Minnesota. It flows southward through the central United States for 2,340 miles (3,770 kilometers). In southeastern Louisiana, the river empties into the Gulf of Mexico. Along the way, the Mississippi borders ten states.

CITIES ON THE RIVER

A number of important cities are located on the Mississippi River. Before railroads and roads were available, these cities shipped and received goods by keelboats, steamboats, and other vessels on the river. Today, coal, oil, grain, and other goods travel on barges along the river.

The biggest cities along the Mississippi are St. Paul and Minneapolis in Minnesota, St. Louis in Missouri, Memphis in Tennessee, and New Orleans in Louisiana.

CLAIMING THE RIVER

Native Americans lived along the Mississippi before European settlers arrived. Algonquian Indians gave the river its name. The name means “big water” in the Algonquian language.

Traders and colonists from France were the first Europeans to settle along the river. In 1682, French explorer René-Robert Cavelier, sieur de La Salle, claimed all the land drained by the Mississippi for France. In 1803, the United States bought the land west of the Mississippi from France. It was called the Louisiana Territory.

FLOODING

Heavy rains and melting snow sometimes cause the Mississippi to overflow its banks. It can cause severe flooding of nearby plains. A flood along the Mississippi in 1993 ranks among the nation’s worst disasters. Towns and farms from Minnesota to Missouri were flooded.

Levees, or high walls of dirt, line much of the Mississippi River. They help keep it from spilling over.

Nile River

There are long rivers, and there are famous rivers. The mighty Nile is the world’s longest and most famous river. The Nile’s longest branch stretches 4,160 miles (6,695 kilometers) and crosses half a continent.

The Nile winds north from the heart of Africa. Crocodiles and hippopotamuses live in its waters. Gigantic pyramids built by ancient Egyptians rise along its banks.

WHERE DOES THE NILE BEGIN?

For centuries, the source of the Nile River was a great mystery. The river passes through many landscapes on its journey, including thick rain forests, swamps, and deserts. Explorers had difficulty tracing the river to its beginning.

Today, we know that the main branch of the Nile starts just above Lake Victoria in east central Africa. The river begins as little more than a trickle.

WHERE DOES THE NILE FLOW?

From its humble beginnings, the Nile flows into Lake Victoria, the world’s second largest freshwater lake. The Nile draws much of its water from this great lake.

The Nile flows out of Lake Victoria to the north. The river crosses Uganda into Sudan, where it spreads out to form a massive swamp.

At the city of Khartoum, Sudan’s capital, another great river called the Blue Nile joins the White Nile—the river’s main branch. Together, they form one very powerful river.

At Sudan’s northern border, this river thunders over six waterfalls. From there, it winds through Egypt’s famous Nile Valley before reaching the Mediterranean Sea.

Where the Nile meets the sea, it fans out into a broad river delta that looks like a big triangle. This triangle is called the Nile River Delta.

A RICH HISTORY

Ancient Egypt, the first great African civilization, started along the banks of the Nile more than 5,000 years ago. Ancient Egypt ruled the Nile Valley for thousands of years. Its people built great pyramids, temples, and other monuments you can still visit today.

Rich farmland along the banks of the Nile made this ancient civilization possible. Every year, the Nile flooded its banks. The floodwaters covered the banks with a fertile soil called silt. The Nile’s banks were easy to farm and produced lush crops.

The Nile also made a perfect highway for boats. The river current flows north, but the wind on the river blows south. To go south, boaters put up sails to catch the wind. To go north, they took the sails down. Ancient people traded along the river for hundreds of miles.

THE NILE TODAY

Today, the Nile no longer flows free. Many dams rise up along the Nile to capture water. They help control flooding and provide electricity. But they also have contributed to pollution of the Nile.

The largest and most famous dam is the Aswan High Dam, completed by the Egyptian government in 1970. It created a giant lake called Lake Nasser.

Water from Lake Nasser drives huge engines that make electricity. The dam supplies most of Egypt’s electric power. Factories have sprung up along the Nile to use this power. Their wastes pollute the river.

The Aswan High Dam controls the flooding of the Nile below it. But it also stops silt from flowing downstream. Egyptian farmers must now use chemical fertilizers to replace the silt. These, too, pollute the river.

Oceans

When most people think about Earth, they think about land. You’ve probably spent your entire life on land. If you look at a globe, however, you can see that there is not as much land as water. Most of the Earth is covered by water, and most of that water is salty. Almost all of the salt water is connected into one huge ocean. The ocean covers almost two-thirds of the Earth.

The World’s Oceans
Ocean	square miles	square kilometers

Pacific Ocean	63,980,000	165,700,000
Atlantic Ocean	31,810,000	82,400,000
Indian Ocean	28,360,000	73,440,000
Arctic Ocean	5,430,000	14,060,000

ONE OCEAN OR MANY?

There is only one world ocean. Big pieces of land called continents divide the world ocean into parts, but all of the parts are connected. The four major parts are called the Atlantic Ocean, the Pacific Ocean, the Indian Ocean, and the Arctic Ocean.

Parts of some oceans are called seas. The Caribbean Sea and the Mediterranean Sea are part of the Atlantic Ocean. The Coral Sea is part of the Pacific Ocean.

HOW DEEP IS THE OCEAN?

The ocean is not very deep at the beach. Water along seashores might not even cover your toes. You can wade out into the ocean. You can stand on the bottom near a beach.

Farther out, the ocean is very deep. The deepest parts are in the Pacific Ocean. A place called the Mariana Trench is almost 7 miles (11 kilometers) deep!

Some parts of the ocean floor are flat. Other parts have underwater mountains. The Mid-Atlantic Ridge is a mountain range under the Atlantic Ocean. Melted rock called magma oozes up from cracks along the Mid-Atlantic Ridge. The magma cools and makes new rock.

IS OCEAN WATER WARM OR COLD?

The ocean is freezing cold in some places and very warm in others. The Arctic Ocean near the North Pole and the ocean in the south around Antarctica are freezing cold. You can see icebergs floating in these oceans.

Ocean water near the equator is always warm. The equator is an imaginary line around the middle of Earth. You can swim in the ocean near the equator all year long.

CURRENTS IN THE OCEAN

The ocean has “rivers” of cold or warm water running through it. These “rivers” are called currents. One of the best-known currents is the Gulf Stream. The Gulf Stream carries warm ocean water from the equator up to the north part of the Atlantic Ocean.

Warm and cold ocean water is always moving around the world. In some places cold water comes up from deep in the ocean. Warm water sinks down. Wind blows ocean water at the surface. Waves also move ocean water. Changes in ocean currents can make weather changes on land. Sometimes the changes cause mild winters in some places and lots of rainfall in other places.

WHAT LIVES IN THE OCEAN?

The ocean is full of living creatures. The tiniest ocean creatures are plankton. Plankton drift on the surface. The biggest ocean animal is the blue whale. The blue whale can be 80 feet (24 meters) long. It is the biggest animal on Earth.

Many kinds of fish and shellfish live in the ocean. Your tuna sandwich comes from the tuna, a fish that swims in the ocean. Crabs, lobsters, and shrimp crawl around on the ocean floor. Squid and octopus dart about with their long arms and tentacles.

Different creatures live at different ocean depths. Very strange creatures live deep in the ocean where there is no sunlight. Some deep-ocean fish glow in the dark. Some of them are blind.

PROTECTING THE OCEAN

Oceanographers are scientists who study the ocean. They worry about ocean pollution. Thousands of ships carry oil and other goods across the ocean. Oil spills from ships can pollute the ocean. People build factories close to the ocean shore. Chemicals from factories can pollute the oceans. Chemical bug killers from farms can also drain into the ocean.

People get many things from the ocean. Fish and other food come from the ocean. It is important to keep ocean water clean.

Ships

Every day, huge ships made of steel cross the oceans and travel the world’s great rivers and lakes. Powerful engines turn propellers that make the ships go. Ships transport people and goods to all parts of the world.

Ships are very important to the way we live. Ships carry oil that is made into gasoline for our cars. They bring in much of the food we eat and the clothes we wear. They carry computers, furniture, and televisions for our homes. Look around you. Many of the things you see traveled to where you are on a ship.

THE PARTS OF A SHIP

Ships may look very different from each other, but they all have the same basic parts. All ships float in water. The part that floats is called the hull. Inside the hull there are decks. Decks are like the floors in a building. You can go up and down from one deck to another.

HOW SHIPS MOVE THROUGH WATER

The front of a ship is called the bow. The back is called the stern. Attached to the stern is a wooden or metal plate called the rudder. A steering wheel or a stick called a tiller makes the rudder swing back and forth. Moving the rudder makes the ship turn.

Some ships use sails to move. Sails are big sheets of fabric. The sails hang from a long pole called a mast. Ships with sails use the energy of blowing wind to move through the water.

Most modern ships have engines that burn fuel. Engines make power to turn propellers at the stern. Propellers make ships go through the water.

THE AGE OF SAILING SHIPS

By about 5,000 years ago, the Egyptians were building some of the first sailing ships. They made them by tying bundles of reeds to a wooden frame. The ships carried cargo and had one or two square sails.

The best ancient shipbuilders were the Phoenicians. They made cargo ships and warships called galleys. Galleys had sails and many oars.

The ancient Greeks fought with the Phoenicians. The Greeks added a big spike to the front of their galleys. They used the spike to ram into Phoenician ships.

In China and other parts of Asia, builders made cargo ships called junks. Junks had a flat bottom, a square bow, and a rudder. The sails had pieces of bamboo in them to make them stiffer.

Arab builders began to use triangular sails called lateens. A ship with lateen sails could sail almost directly into the wind.

In the 1200s, Europeans began building ships with three masts and many square and triangular sails. These ships were called full-rigged ships, or square-riggers. Starting in the 1400s, European explorers set off on voyages in these ships to faraway parts of the world. Christopher Columbus, Vasco da Gama, and other explorers used square-rigged ships.

In the 1600s, the Spanish built huge ships called galleons. In the 1700s and 1800s, the British built big sailing ships that they used to fight sea battles.

The fastest sailing cargo ships were the clipper ships of the mid-1800s. They had sleek, narrow hulls and as many as six sails on each tall mast.

MODERN SHIPS

During the 1800s, iron and steel hulls replaced wooden hulls. New types of engines were also developed. For the first time, ships could move without wind or human-powered oars. Steam engines fueled by coal replaced sails.

Later, engines that used oil as a fuel replaced steam engines. Today, most ships have steel hulls and are driven by powerful motors that turn big propellers.

CARGO SHIPS

There are many kinds of cargo ships. Container ships carry cargo in huge boxes the size of railroad cars. Oil tankers and supertankers carry oil in their hulls. Freighters transport tons of coal, grain, and ore.

PASSENGER SHIPS

There were no passenger ships in ancient times. Travelers had to look for space on a cargo ship. Most passengers slept wherever they could find a spot on the deck. After Europeans learned about the Americas and Australia, settlers wanted to move to these new lands. Full-rigged ships carried passengers along with cargo. It was not very comfortable traveling on those wooden sailing ships.

By the mid-1800s, shipping companies began to offer regular passenger service. Companies competed with each other for passengers. They built luxurious ocean liners that could cross the Atlantic Ocean in just a few days.

In the 1950s, airplanes became more popular than ships for traveling over oceans. Today, most passenger ships are cruise ships. You can take a vacation aboard big cruise ships.

NAVY SHIPS

For many years, battleships were the biggest warships. They were used in World War I and World War II. Today, aircraft carriers are the biggest warships. The largest carriers can hold 85 airplanes. They have crews of more than 5,500 people.

Modern navies have many other kinds of ships. Submarines are ships that can dive underwater. Some submarines carry missiles to attack enemy ships. Cruisers escort and defend aircraft carriers from attack by planes and submarines. Destroyers defend carriers and merchant ships from air and submarine attacks. Frigates escort and defend ships from submarines.

THE NEWEST SHIPS

Shipbuilders are looking for ways to build big ships that go faster and carry more cargo. They are looking for new hull shapes that go faster in the water. They are also looking for better engines. Water jet engines may replace propellers. A jet boat engine works by shooting out water, just as a jet plane engine shoots out air.

Washington, D.C.

Washington, D.C., is a great place for a field trip. Tens of thousands of school kids go there every year. What’s so great about Washington? It’s the capital of the United States.

The D.C. stands for District of Columbia, the name of the capital territory. Washington is the name of the city that fills the entire District of Columbia.

SEE THE WHITE HOUSE

The president of the United States lives in the White House, a beautiful mansion at 1600 Pennsylvania Avenue in the middle of Washington, D.C. The White House has 132 rooms! You can visit it to see where former presidents lived and worked.

The White House is America’s oldest federal (national government) building. George Washington, the first U.S. president, helped lay the building’s first stone in 1792. John Adams, the second president, was the first president to live in the White House.

VISIT CONGRESS

Congress meets to debate and vote on new laws in the Capitol. That’s a building where the representatives and senators from your state help run the nation. Congress has 535 members: 435 representatives and 100 senators. You can visit the Capitol and watch them work.

THE NATION’S ATTIC

“The nation’s attic” is what some people call the Smithsonian Institution. It’s the largest museum complex in the world. The Smithsonian owns dinosaur bones, historic airplanes, a zoo full of wild animals, famous paintings, and millions of other neat things.

At the Smithsonian’s Air and Space Museum you can see the first airplane. The Wright brothers flew it in 1903. The museum also has the command module from Apollo 11. Apollo 11 was the first mission to land on the Moon.

The Smithsonian’s Museum of National History owns more than 1,500 dinosaur specimens. Center stage is the meat-eating Allosaurus and the 87-foot-long (27-meter-long) vegetarian Diplodocus. The museum also has a collection of famous gems and jewelry. You can go there to see the Hope Diamond, a rare blue diamond almost as big as a golf ball!

PRESIDENTIAL MONUMENTS

No building in the District of Columbia is taller than the Washington Monument. It’s 555 feet (169 meters) high. That is taller than a 50-story building. The Washington Monument was constructed to honor the memory of George Washington.

Inside the round building of the Jefferson Memorial stands a bronze statue of America’s third president, Thomas Jefferson. Jefferson was the author of the Declaration of Independence.

A marble statue of President Abraham Lincoln sits inside the Lincoln Memorial. His short Gettysburg Address is inscribed on a marble wall. He delivered this speech in 1863 during the Civil War. The Lincoln Memorial is where 200,000 people in 1963 heard Martin Luther King, Jr., give his famous “I Have a Dream” speech. This speech expressed the hopes of the civil rights movement in moving words.

The newest presidential memorial is dedicated to Franklin D. Roosevelt. He was the 32nd president of the United States. Roosevelt led the nation through the difficult years of the Great Depression (1930s) and World War II (1939-1945). A 7-acre park of gardens, waterfalls, and bronze statues dedicated to his memory opened in 1997.

Paris

Paris is the capital of France. It’s known as the City of Light because of its beauty. It’s a place to enjoy great food, great art, and great buildings. It’s also a place to sit back and enjoy life in a sidewalk café.

For hundreds of years, artists and writers have celebrated Paris. Many have gone to live there. Visitors come to admire the city. It’s a center of fashion and style. It’s also the business, financial, and industrial center of France.

THE EIFFEL TOWER

The Eiffel Tower is the best-known landmark in Paris. France built this lacy, iron tower for the Paris World’s Fair of 1889. The fair honored the French Revolution that began in Paris 100 years earlier.

The Eiffel Tower rises nearly 1,000 feet (300 meters). Elevators take visitors to the top. At the time it was built, the tower was the tallest structure in the world. The tower was named for its designer, Gustave Eiffel.

CITY ON THE SEINE

The river Seine runs through Paris and cuts it in half. The part of Paris on the north side of the river is called the Right Bank. The part on the south side is called the Left Bank.

Most of the businesses and large stores in Paris are on the Right Bank. Many government buildings and the University of Paris are on the Left Bank. The university is in the Latin Quarter. Students at the university originally spoke Latin, giving the neighborhood its name.

The oldest part of Paris is on the Île de la Cité, an island in the Seine. Notre Dame cathedral is on the island. Workers began to build the cathedral in 1163.

BUILDINGS AND MONUMENTS

There’s a lot to see in Paris. You could take a walk down the Champs-Élysées. This wide, tree-lined boulevard is one of the most famous streets in the world.

At one end of the Champs-Élysées is the Arc de Triomphe (Arch of Triumph). This monument was built to honor the victories of French emperor Napoleon I. At the other end is the Place de la Concorde (Square of Peace) with its huge fountains and statues.

The Louvre is an old palace in the middle of Paris. It’s also one of the world’s great museums. Leonardo da Vinci’s famous painting, the Mona Lisa, is here. If you like paintings by the French impressionists, be sure to visit the Musée d’Orsay. This museum used to be a railroad station.

When you’re tired, sit for a while in one of Paris’s pleasant parks. The Tuileries Gardens are on the Right Bank, and the Luxembourg Gardens are on the Left Bank.

London

London is the capital of the United Kingdom and the home of its queen, Elizabeth II. It’s also the largest city in Europe. About 7 million people call London home.

LONDON LANDMARKS

Millions of people visit London every year from all over the world. If you travel there, you’ll find many fascinating things to see and do.

During August and September, you can visit Buckingham Palace. That’s where the queen lives most of the year. It has about 600 rooms, but you’ll see only state rooms where the queen entertains guests. In the morning, a colorful ceremony called “changing of the guard” takes place in the palace courtyard. One group of palace guards marches off duty, and another troop arrives to replace them.

You can tour the Tower of London, a historic fortress that was once a royal palace. It was also used as a prison for hundreds of years. Two of the wives of King Henry VIII—Anne Boleyn and Catherine Howard—were put to death here. The Crown Jewels are a popular attraction at the Tower. This collection of jeweled crowns, swords, scepters, and other royal objects is only used on special occasions, such as the crowning of a new ruler.

Be sure to visit Westminster Abbey, one of Britain’s famous churches. The nation’s kings and queens are crowned here. Many rulers and famous citizens are buried here. There are also monuments to political figures and poets.

The Houses of Parliament are along the Thames River, near Westminster Abbey. This is where the government meets. Look up to see the clock tower with Big Ben, London’s famous bell that rings every hour. You can get on a boat nearby for a ride on the Thames.

Other places you might want to see are Scotland Yard, Madame Tussaud’s, and the British Museum. You can find out about London’s famous criminals in the Crime Museum at Scotland Yard, the home of London’s Metropolitan Police. At Madame Tussaud’s, you’ll see eerily realistic, life-size wax figures of pop idols and historic figures. A great thing to see at the British Museum is the collection of mummies, tomb paintings, and gold jewelry from ancient Egypt. The museum’s Egyptian collection is one of the largest in the world.

For a good view of London, take a ride in the London Eye. This enormous wheel takes you 443 feet (135 meters) above the London skyline. Unlike a traditional Ferris wheel, the London Eye carries its passengers in enclosed compartments.

GETTING AROUND

A quick and easy way to get from place to place in London is by Tube, a network of underground trains. You’ll see more, however, if you travel around London by bus. Sit upstairs on London’s double-decker buses for a good view.

AN OLD CITY

London is nearly 2,000 years old. It was founded by the ancient Romans soon after they invaded Britain in ad 43. The city has been sacked (destroyed) several times by invaders. It has also been destroyed by fire. In 1666, the Great Fire of London burned down a large part of the city.

During the18th and 19th centuries, London was the world’s largest city. It sat at the center of a vast and powerful British empire that circled the globe. The city was heavily damaged by German bombing during World War II (1939-1945). The damaged areas were rebuilt after the war.

AN INTERNATIONAL CITY

The residents of this sprawling city today are a mix of many races and nationalities. Many Londoners come from former British colonies, such as India, Pakistan, Jamaica, South Africa, and Hong Kong. This makes London one of the world’s most international cities.

Architecture

We ask for a lot from our buildings. They have to keep out the rain, wind, rats, and bugs, not to mention our enemies. They need to store our stuff, keep us warm when it’s cold, and keep us cool when it’s too hot. We also like our buildings to be well constructed and beautiful.

Architecture is the important art and science of making buildings. Architects are the bosses who design buildings and supervise their construction.

WHAT ARE BUILDINGS MADE OF?

Buildings once were made of whatever materials were available. Where forests grew, for example, people used wood. Where there were no trees, people used the earth itself. They dried mud in the sun to make bricks. In the far north, they used blocks of snow or ice.

These materials aren’t long-lasting, however. Mud bricks wear away. Wooden buildings catch fire and burn down.

Stone won’t catch fire, and it can be expected to endure. Many kinds of stone, including marble and limestone, are good materials to build with. Steel is strong and lightweight. It lets architects build tall buildings, like skyscrapers.

But deciding on what materials to use isn’t usually the first thing an architect thinks about. The architect needs to know the reason for the building. How will the building be used?

REASONS FOR BUILDINGS

Shelter is the most basic reason for building. Buildings shelter us at home, at work, and at play. All buildings must shelter us from rain, wind, sun, and cold.

Buildings also provide security. Some of the world’s most permanent structures were built to defend against enemies. Castles had moats and drawbridges to keep enemies out, and high walls from which to pour down boiling oil on them.

Some of the most impressive buildings provide places for worship. Temples, churches, and mosques must meet spiritual needs. The soaring heights of a Gothic cathedral, for example, inspire amazement and admiration.

Some buildings are just for showing off. Kings and emperors insisted on grand palaces and castles. People with money have always demanded that architecture display their wealth. Today, large corporations, governments, and universities demonstrate their importance by putting up impressive buildings.

Architects today design all kinds of buildings. Our way of life calls for office buildings, large apartment complexes, shopping centers, schools, hospitals, airports, and hotels.

LANDMARK ARCHITECTURE

We judge the beauty of architecture in various ways. Some buildings have been judged especially great. In the past, architects lavished attention on religious structures. Today, many of the most exciting buildings are museums and houses.

Many people think the Greek temples are the most beautiful shrines of all time. The Greeks put columns around the outside of their temples. One masterpiece is the Parthenon, a temple on a hilltop in Athens, Greece. We admire its simplicity, but the carvings on the temple were once painted bright colors.

Saint Peter’s in Vatican City was a major project of the 1500s. With its dome by Michelangelo, Saint Peter’s influenced many state capitol buildings in the United States.

America’s most famous architect is Frank Lloyd Wright. A number of his buildings are national landmarks. Most famous are the Guggenheim Museum in New York City and Fallingwater, a house in Pennsylvania. The Guggenheim’s spiraling ramp provides a dramatic showcase for artwork. Fallingwater overlooks a stream and waterfall. Its terraces appear to project from the surrounding hillside.

Frank Gehry designs buildings that combine many irregular shapes. His Guggenheim Museum in Bilbao, Spain, uses titanium metal to create a curving, lightweight surface that shimmers in sunlight.

Europe

“Europe”—the word calls to mind a land of famous old buildings, scenic countryside, and time-honored traditions. Europe is rich in history. Ancient stone castles, lavish palaces, and beautiful cathedrals dot the land. But it’s also one of the world’s most vibrant, modern places.

Europe attracts visitors from around the world. They come to see its historic landmarks, world-class art museums, and great natural beauty. Scenic attractions include the rolling green hills of the British Isles, towering peaks of the Swiss Alps, and sunny Mediterranean beaches.

PENINSULAS AND ISLANDS

Europe is considered a separate continent. But it’s actually a peninsula—a piece of land that juts out from a mainland into water. Europe is a giant peninsula sticking west out of Asia, the mainland.

The Ural Mountains east of Europe divide the continent from Asia. The mountains run right through Russia. Russia lies partly in Europe and partly in Asia.

Europe has many smaller peninsulas of its own. Greece and Italy are peninsulas. Spain and Portugal share another peninsula called Iberia. In the north, Denmark occupies the small peninsula of Jutland. Sweden and Norway occupy the larger Scandinavian Peninsula.

Europe also includes many islands, such as Great Britain, Ireland, Sardinia, Corsica, Sicily, and Crete. All of these islands and peninsulas give Europe a long coastline and many harbors, inlets, and seaports.

A CROWDED CONTINENT

Europe is the second smallest of the world’s seven continents. Only Australia is smaller. Europe is about the same size as the United States. Yet it has almost three times as many people.

About 729 million people live in Europe. That makes it the most crowded of all the continents. Europe is divided into more than 40 countries, and Europeans speak more than 60 languages.

Europe is home to dozens of great cities. Many of them, such as London and Paris, date to ancient times. Among Europe’s other famous cities are Athens, Berlin, Budapest, Madrid, Moscow, Prague, Rome, and Vienna.

MANY LANDSCAPES

You can see a great variety of landscapes in Europe. Many hills and mountains cover northwestern Europe. Around Norway’s coast, ancient glaciers carved deep inlets to the sea called fjords. Steep mountains thick with timber line the fjords, creating beautiful scenery.

South of these highlands lies the Great European Plain. This low-lying plain reaches all the way from southern France to the Ural Mountains in Russia. Some of Europe’s best soils and most productive farms are found here.

Europe’s highest mountains rise to the south of this plain. In the west stand the spectacular, snow-capped Alps. These jagged peaks include the world-famous Matterhorn. The Alps cover parts of Switzerland, France, Italy, and Austria. High mountains reach all the way to the northern shore of the Mediterranean Sea.

Europe’s tallest and steepest peaks, the Caucasus Mountains, stand in the southeast. They are home to Elbrus, the highest point in Europe at 18,510 feet (5,642 meters).

GREAT CIVILIZATIONS

The first great European civilizations arose along the calm waters of the Mediterranean Sea. The greatest of these was ancient Greece, which grew up on the islands and peninsula of Greece about 2,500 years ago.

The center of power then shifted to ancient Rome. Starting in Italy, the Romans built an empire around the Mediterranean coast. Then they pushed north, through France and the British Isles, and east as far as Iraq.

Greece and Rome laid the foundations for modern Europe. The Greeks made astounding advances in math, science, philosophy, and the arts. They invented democracy. The Romans made great strides in engineering, government, and law. They invented cement. Some Roman-built roads, canals, and bridges are still used today in Europe.

A CHRISTIAN CONTINENT

Christianity spread to Europe from the Middle East during Roman times. For many centuries, almost all the people of Western Europe belonged to the Roman Catholic Church. Most Eastern Europeans belonged to the Orthodox Christian Church. That church was based in Constantinople, a city on the eastern edge of Europe.

Europeans today are still mostly Christian. But not all Western Europeans are Catholic anymore. Almost half are Protestants. Small minorities follow other religions, including Judaism, Islam, and Buddhism.

THE RISE OF EUROPE

After the Roman Empire began to break apart in the ad 300s, Europe entered a period called the Middle Ages. Many small kingdoms arose to take the place of Roman rule. Struggles for power between kings and other nobles frequently broke the peace. Trade collapsed. Hardly anyone could read.

Gradually, the power of the kings increased. They built strong kingdoms across Europe, with powerful armies and navies to defend them. By the 1400s, Spain and Portugal had become great powers. They sailed all over the world and founded empires in Asia, Africa, and the Americas. Later, The Netherlands, Britain, and France built impressive overseas empires.

Meanwhile, Europeans began questioning their traditional beliefs. They questioned the power of the Catholic Church. Great progress was made in science and the arts. In the 1700s and 1800s, Europeans invented new power-driven machines for making goods. Big factories emerged. This was called industrialization. It made Europeans rich and powerful.

FREEDOM IN EASTERN EUROPE

In 1917, a group called the Communists took over Russia in eastern Europe. They turned Russia into an empire called the Soviet Union. Over time, the Soviet Union gained control of many other eastern European countries. Communist governments tried to control most aspects of life in their countries.

In the 1980s, the Soviet Union crumbled. Russia and other Eastern European countries gained their freedom.

EUROPE TODAY

The years of Communist rule left their mark on Eastern Europe. The Communists built inefficient factories that polluted the environment. Few Eastern Europeans prospered under Communism. Today, this is changing. Eastern Europeans are modernizing their countries and working to build new sources of wealth.

By the late 20th century, European countries had given up most of their remaining overseas colonies. Yet Europe remains a wealthy and powerful place. Today, as in centuries past, Europe is a world leader in art, science, industry, and learning.

Africa

Africa is often called the cradle of humanity. It was in Africa that humans first arose long, long ago. From Africa, these people migrated into Asia, Europe, Australia, and the Americas.

Today, Africa is home to a remarkable variety of people and cultures. It is a land of striking contrasts and wild beauty. It is also a place facing many problems, including war, starvation, poverty, and disease.

A VAST CONTINENT

Africa is the second largest of Earth’s seven continents, after Asia. It accounts for nearly one-quarter of the world’s land. In the northeast, Africa touches Asia in Egypt. In the northwest, Africa almost touches Europe in Morocco. More than 50 nations are found in Africa. They are home to some 800 million people.

STRADDLING THE EQUATOR

Africa is the only continent that truly straddles the equator, the imaginary line that encircles Earth around its middle. Much of Africa is hot and dry. Only central Africa has a tropical rainy season. Yet few areas of the world are as diverse as Africa.

THE MIGHTY NILE

The longest river in the world, the Nile, empties into the Mediterranean in northeastern Africa. Ancient Egypt, one of the world’s first great civilizations, developed along the mighty Nile more than 5,000 years ago. Today, its magnificent pyramids still tower above the land.

THE SAHARA

The Sahara, the world’s largest desert, reaches across a vast swath of northern Africa. It stretches from the Atlantic Ocean in the west to the Red Sea in the east. In fact, the Sahara covers one-quarter of the entire continent. The Sahara is mainly hot, dry, and empty. But people have used teams of camels to carry goods across this giant desert since ancient times.

EQUATORIAL AFRICA

South of the Sahara is equatorial Africa, lying on either side of the equator. Here we find lush tropical rain forests and tropical grasslands called savannas. On Africa’s west coast are the trading ports of West Africa. These ports ship crops such as coffee, cotton, and cacao beans (from which chocolate is made) to the world.

The Congo River, Central Africa’s largest waterway, empties into the Atlantic Ocean near the equator. The Congo drains a vast basin in Central Africa that receives more rainfall than any other part of the continent. It carries more water than any river in the world except the Amazon River in South America.

GREAT RIFT VALLEY

The highlands of Africa are in the east. They run the length of the continent. Between mountain ranges lies the Great Rift Valley. It runs north to south for more than 3,000 miles (4,830 kilometers). The valley actually begins in the Asian country of Syria and reaches all the way to Mozambique in southeast Africa. The Great Rift Valley is rich with fossils. Here, scientists have found ancient bones that have helped them understand the mystery of human origins.

KILIMANJARO

Africa’s tallest mountains are found in the towering ranges of the east. Kilimanjaro, the highest mountain in Africa, rises in east central Africa. A dormant volcano, Kilimanjaro climbs to 19,341 feet (5,895 meters).

SOUTHERN AFRICA

In southern Africa is the great Namib Desert. This desert lines the southwest coast, reaching inland about 81 miles (130 kilometers). In the center is the fertile High Veld, a large plateau that slopes down to the Indian Ocean in the east. On the southern tip of the continent is South Africa’s famous Cape of Good Hope. This is the place where the Indian and Atlantic oceans meet.

MANY DIFFERENT PEOPLE

The people of Africa may be the most diverse of all the continents. Africa’s 800 million people speak perhaps 2,000 or more languages. Thousands of distinct ethnic groups are found in Africa.

North of the Sahara, people are mainly of Arab origin. South of the Sahara, the people are mostly black Africans. Throughout Africa are scattered people of European ancestry, descendants of colonial settlers.

Most Africans live in rural communities. Many raise livestock or farm. Relatively few people live in cities. But Africa does have many big cities, and they are growing rapidly. They include Cairo, Egypt; Casablanca, Morocco; Lagos, Nigeria; and Cape Town, South Africa.

From the 1500s to the 1800s, millions of Africans were forcibly removed to North and South America to work as slaves. Their descendants are still prominent among the people of both of those continents.

A WILD PLACE

Africa is famous for its stunning wildlife. The continent is home to thousands of species of mammals, birds, reptiles, amphibians, fishes, and insects.

South of the Sahara, Africa teems with animal life. Wild herds of antelope, zebras, giraffes, and impalas roam across the savanna. Lions, cheetahs, and leopards feed on them. Elephants live in some forests and grasslands. Gorillas live in the rain forests of Central Africa.

Today, many of these animals are endangered. Farms and cities have replaced much of the land they called home. They have been hunted for trophies, meat, and sport. Many countries in Africa try to protect endangered animals, but their numbers continue to dwindle.

MANY CHALLENGES

Today, Africa faces many challenges. The majority of its people remain poor. Droughts are frequent in many areas, leading to terrible starvation. Wars within and between countries have killed millions of people and forced millions of others to leave their homes and live elsewhere as refugees.

Diseases such as tuberculosis and malaria kill millions of Africans each year. In recent years, acquired immunodeficiency syndrome (AIDS) has spread rapidly, especially south of the Sahara. It has infected millions of people and devastated some regions.

Despite these troubles, Africa remains a magnificent place. Perhaps no other part of Earth is as varied in its geography, wildlife, and people.

Asia

Imagine mountains that seem to touch the sky and long rivers that wind through rich farmland. Imagine lush tropical rain forests full of unusual animals and huge cities teeming with millions of people. Imagine all of this and you’ll have an idea of what Asia is like.

LAND OF EXTREMES

Asia is a land of extremes. It’s the biggest of the seven continents. In fact, it covers about 30 percent of all the world’s land. Asia is so big it touches Europe in the west and nearly reaches North America in the east!

In northern Asia are the vast frozen lands of Siberia. In the south are the damp tropical forests of Malaysia and Indonesia. Asia has large, crowded cities like Mumbai (Bombay), India. It has huge, empty inland deserts like the Gobi in China. Seven of the ten longest rivers in the world flow through Asia.

Asia has the world’s highest point at Mount Everest in Nepal. It has the lowest point, too. That’s near the Dead Sea, in an area of southwest Asia called the Middle East.

At any given moment there are places in Asia that are very hot and others that are very cold. There are places that are dry as a bone and others that are rainy and wet.

CRADLE OF CIVILIZATIONS

In the Middle East, archaeologists have found traces of the world’s oldest known cities. The oldest is Jericho. It’s a city in the West Bank between Israel and Jordan. Jericho dates back more than 8,000 years.

The Middle East is often called the “cradle of civilization.” It was here, in Mesopotamia (now Iraq), that people first began to settle into communities and grow grains. That was over 10,000 years ago. Both China and India are also home to other great early civilizations.

MANY RELIGIONS

Did you know the world’s five biggest religions began in Asia? The Middle East is the birthplace of Judaism, Christianity, and Islam. India is the ancient home of Hinduism and Buddhism.

All of these religions are still practiced by millions of people in Asia. Sometimes they are the source of great conflict between Asian societies.

PEOPLE AND MORE PEOPLE

Asia has lots of people. Nearly 4 billion of them! About three of every five people in the world live in the 48 countries of Asia. China and India are the two most populated countries in the world, each with over 1 billion people.

To understand everyone in Asia you would have to learn more than 1,000 languages. Can you imagine 1,000 languages? What could they all possibly sound like?

POVERTY AND WEALTH

Many of Asia’s people are very poor. But many others are very rich. In countries such as Afghanistan, India, China, and Bangladesh, millions of people live without electricity or even clean water. In places like Japan and South Korea, millions of people live in wealthy towns and cities. They create, make, and use much of the world’s new technology.

Rich and poor and old and new. That’s Asia for you: a land of extremes.

Sahara

Two thousand camels plod along a dried-up riverbed. The camels are being driven to market. Their destination is hundreds of miles away, in Egypt. The journey takes many weeks.

For as far as the eye can see, the camels and their herders are the only signs of life. This is the world’s largest desert. This is the Sahara.

SAHARA MEANS “DESERT”

The name Sahara comes from the Arabic word for “desert.” It is a vast region that extends across parts of ten countries in northern Africa. The Sahara stretches the entire width of the continent, from the Atlantic Ocean in the west to the Red Sea in the east. In fact, the Sahara is almost as large as the United States!

HOT, COLD, AND VERY DRY

In this great desert, daytime temperatures can be scorching. The highest outdoor temperature ever recorded, 136° Fahrenheit (58° Celsius), was in the Sahara in 1922. In winter, it can get chilly enough at nighttime for water to freeze.

The Sahara is very dry. Most parts of the desert receive just a few inches of rain a year. Some areas receive less than 1 inch (2.5 centimeters) a year. In other areas, years pass without any rain at all.

THE LAND

The western Sahara is a region of rocky plains. The central Sahara has several mountain ranges. Some of the highest mountains have snow all year. The eastern region is the driest. It is mostly sand dunes. Some dunes extend for hundreds of miles!

OASES

In the Sahara’s interior, no permanent streams flow across the surface. Dried riverbeds fill with water only when it rains. But water does rise to the surface in places, mostly from springs and wells. These areas are called oases.

There are hundreds of oases scattered across the Sahara, mostly along its edges and in mountainous areas. Oases can support abundant plant and animal life.

Outside the oases, only short, thorny bushes grow. But the bushes support plant-eating animals such as antelope and gazelles. Jackals, foxes, and hyenas prey on the plant eaters.

WHO LIVES IN THE SAHARA?

Until about 5,000 years ago, the Sahara was wet enough to support fertile grassland. Farmers grew crops and raised cattle. Ancient rock paintings show the human and animal life of this time. But as the region dried up, the farmers left.

For thousands of years afterward, the Berber and other desert people have lived and traded in the Sahara. Their camels have carried gold, salt, and other goods between the oases. Thanks to this trade, towns such as Timbuktu (now called Tombouctou) grew into rich cities.

Today, some desert people still trade by camel across the desert. Others have replaced their camels with trucks. In oases, farmers grow date palms, wheat, barley, and vegetables.

Rain Forest

Where would you go to find more kinds of plants and animals than anywhere else on Earth? You would go to a tropical rain forest.

Tropical rain forests are home to an amazing number of plants and animals. A patch of tropical rain forest no bigger than a school parking lot can have almost as many different species (kinds) of trees as there are in all the forests of Canada and the United States!

Biologists believe that more than half of the world’s plant and animal species live in tropical rain forests.

WHAT IS A RAIN FOREST?

A rain forest is a place where there is lots of rain. One kind of rain forest is called a temperate rain forest. You can find temperate rain forests where the weather is cool and mild, and very wet.

A temperate rain forest grows near the Northwest coast of the United States. Just a few kinds of evergreen trees grow there. Most of the world’s rain forests are tropical rain forests with many kinds of trees.

Tropical rain forests grow in warm places near Earth’s equator. The equator is an imaginary line that goes around the middle of the planet. There are tropical rain forests in Central and South America, Africa, and Asia. The world’s largest rain forest is the Amazon rain forest in South America. It is always hot and wet in a tropical rain forest.

WHAT PLANTS GROW IN RAIN FORESTS?

Different kinds of plants grow in different layers of a tropical rain forest. The ground in a rain forest is called the forest floor. The soil on the forest floor is very thin and poor. Some plants living there get their food from dead plants. Other plants on the ground eat insects. The pitcher plant is an insect-eating plant that grows in rain forests in Asia.

The plant layer just above the forest floor is called the understory. Not much sunlight gets down to this layer. Young trees and plants that like low levels of light grow in the shady understory.

The top layer of the rain forest is called the canopy. The tops of tall trees make up the canopy. They capture most of the sun and rainwater falling on the forest. The canopy is thick and green.

Between the understory and the canopy is a layer called the midstory. Medium-size trees grow in the midstory. Thick vines climb up, around, and between the trees. Mosses, orchids, and other air plants (plants without ground roots) grow on the midstory trees.

WHAT ANIMALS LIVE IN RAIN FORESTS?

Most of the animals that live in a tropical rain forest are insects. The forest is alive with millions of beetles and ants. Bats and beautiful moths fly about at night. Snakes glide silently in and around the trees. Birds are everywhere.

In Africa, wild pigs, gorillas, and other large animals live on the forest floor. Elephants walk through the rain forests of Asia and Africa. Jaguars hide in South American forests and wait for prey, such as a wild pig, to go by.

Most of the rain forest animals live in the canopy. Monkeys swing from branch to branch in the rain forests of Central and South America.

WHY ARE RAIN FORESTS IMPORTANT?

Rain forests are home to huge numbers of plants and animals. Scientists are discovering new ones all the time. Some rain forest plants are used for medicine. Scientists believe there may be many other plants that could be used to treat cancer and other diseases.

Rain forests are like the “lungs” of planet Earth. The trees take up a gas called carbon dioxide. They give off a gas called oxygen. All animals must breathe oxygen in order to live. Too much carbon dioxide in the air could make Earth grow warmer.

For thousands of years, people have lived in the rain forests. People native to the forests hunt wild animals and collect plants for food. They use certain rain forest plants for medicines.

THE LOSS OF RAIN FORESTS

Today, rain forests all over Asia, Africa, and South America are being cut down. Loggers cut down hardwood trees for lumber. Teak, rosewood, and mahogany make beautiful furniture.

Farmers clear the rain forest to plant crops. But the poor rain forest soil soon washes away. Then the farmers must move and clear more rain forest.

People cut roads through the rain forest to reach mines and oil wells. Lumber companies build roads to haul logs. The amount of rain forest cut down every year would fill the state of Wisconsin!

CAN WE SAVE THE RAIN FORESTS?

Conservationists are looking for ways to save the rain forests. Some countries, such as Costa Rica in Central America, have set aside rain forests as national parks.

In other places, poor people need the rain forests for food and wood. Conservationists are looking for ways that people can use the forests without destroying them. People are learning how to grow nuts, seeds, and other crops in the rain forest. They are learning how to make butterfly farms and other places that people can visit on a vacation.

Global Warming

Do you like warm weather? Do you wish it could be warmer still? Be careful what you wish for. The Earth may be moving in that direction. The trend is called global warming.

Not all scientists agree that global warming is happening. Some say it is impossible to know if the climate is changing overall. After all, temperatures vary from day to day and year to year. Most scientists, however, say the trend is up. The warmest days are warmer, the coldest days not as cold. They point out that the ten warmest years of the last century happened after 1980. The three hottest came after 1990. The hottest year on record was 1998.

These scientists say the Earth has warmed up about 1° Fahrenheit (0.6° Celsius) in the last 100 years. The rate of change, they say, is speeding up. A hundred years from now, the Earth may well be as much as ten degrees hotter!

WHAT CAUSES GLOBAL WARMING?

Sunlight brings energy to the Earth. This light turns to heat when it hits the ground. The heat in turn seeps away from the Earth, but the atmosphere slows the heat’s escape. The atmosphere is a layer of air around the planet. It holds in some of the warmth.

The atmosphere is a mixture of many gases. In the last 250 years, this mixture has been changing. The amounts of gases such as methane and carbon dioxide have been rising. These gases trap heat more effectively than other gases. They make the Earth’s atmosphere act like the glass in a greenhouse. It lets sunlight in, but it doesn’t let heat out. As a result, heat is building up close to the surface.

WHY IS THE ATMOSPHERE CHANGING?

People are changing the atmosphere. The changes started hundreds of years ago when people began cutting down forests and burning the wood. The invention of cars and other machines greatly increased the amount of greenhouse gases released into the atmosphere. Such machines burn fuels like wood, coal, oil, and natural gas. When these fuels burn, they add carbon dioxide to the atmosphere. Methane comes from producing coal.

Today, the air contains almost one-third more carbon dioxide than it did in 1750. The amount of methane has doubled.

IS GLOBAL WARMING DANGEROUS?

Global warming could melt the ice at the poles. This would raise the level of the oceans. Water would then cover all the flat coastal lands. People would have less land on which to live and grow food.

Plants and animals are adapted to their climates. If the climate changes rapidly, many may not be able to adapt. Some species will simply die out. Others may spread to cooler climates. There, however, they will be struggling with species already in place.

CAN GLOBAL WARMING BE STOPPED?

Burning less wood, coal, oil, and natural gas will help stop global warming. Scientists recommend that people get more energy from sunlight, wind, tides, nuclear energy, and other sources that don’t burn fuel. Energy sources like these put little or no greenhouse gases into the air.

Scientists say trees can help prevent global warming. All growing plants take carbon dioxide out of the air. Trees do this especially well. They turn the carbon part of carbon dioxide into wood. They release the oxygen. In recent years, people have been cutting down forests all over the world. Scientists say vast new forests must be planted.

WHAT IS BEING DONE?

In 1997, officials from 160 countries met in Kyoto, Japan. They wrote an agreement called the Kyoto Protocol. Countries that sign this agreement promise to burn 5 percent less fossil fuel (coal, oil, and natural gas) by 2012. In 2002, however, the United States decided not to sign the treaty. Russia also has not signed the treaty. Without the United States and Russia, the treaty can’t work.

Antarctica

You are on the highest and windiest continent on Earth. It is also the coldest. Even in summer you need to wear a parka and thick gloves. Almost nothing lives here, although some penguins might waddle past on their way to the sea. You are on Antarctica.

AT THE BOTTOM OF THE WORLD

Antarctica is a large ice-covered continent that surrounds the South Pole. The Southern (Antarctic) Ocean surrounds this frozen land.

Antarctica lies at the bottom of the southern half of the globe. Summer begins there in December and winter in June. In midsummer, the sun shines day and night. It never sets. In midwinter, the sun never rises above the horizon. It is dark day and night.

Antarctica is the coldest place on Earth. It is warmest along the coast, but you would still find it plenty cold. Summer temperatures along the coast reach the freezing point—32° Fahrenheit (0° Celsius). You don’t need ice for your lemonade. If you set it outside, it will freeze. In winter, temperatures inland fall as low as -110° Fahrenheit (-80° Celsius) in the winter.

ICE EVERYWHERE

A huge sheet of ice covers nearly all of Antarctica. At its deepest, the ice is nearly 3 miles (4.7 kilometers) thick. If Antarctica’s ice melted, the world’s oceans would rise by 200 feet (60 meters). Coastal cities around the world would be covered with water as high as a 20-story building.

Its ice cover makes Antarctica the highest of all the continents. Antarctica’s average elevation, or height, is more than 6,500 feet (2,000 meters) higher than any other continent on Earth.

High mountains rise across Antarctica, but the ice sheet covers most of them. Some mountain peaks and rocky areas poke through the ice. Some areas near the coast are also free of ice.

Antarctica’s ice is moving slowly toward the coast. Huge slabs of ice border much of Antarctica’s coastline. Sometimes, large chunks break off to form floating icebergs.

AN ICY DESERT

With all that snow and ice, you might think Antarctica is a really snowy place. But it isn’t. The inland part of Antarctica is one of the driest places on Earth. It gets no rain and very little snow. So how did it get such thick ice?

The ice formed over millions of years. The little snow that fell stayed, because it was too cold for the snow to melt. When new snow fell, it pressed down on the old snow below, and the deeper layers of snow slowly formed ice. The ice got thicker and thicker until it was thousands of feet deep. This process is still going on.

THE ANIMALS OF ANTARCTICA

Antarctica’s climate is too cold and windy for almost all life. The few plants and animals live near the coast. Antarctica’s animals depend on the ocean for food. Penguins and seals spend most of their time in the ocean, but they come onto the ice to have babies. Seabirds also breed along the coast.

The ocean around Antarctica is full of animals. Whales, fish, squids, and jellyfish swim in cold Antarctic waters. The larger animals feed on the smaller animals.

EXPLORING ANTARCTICA

Exploring Antarctica is extremely dangerous. The human body is not built for such cold. At very low temperatures, frostbite can injure skin and other tissues. Even your breath freezes. Explorers must bring all their supplies. They won’t find any food in Antarctica. They must carry and build shelters from the cold. Without proper shelter, they will die.

Antarctic blizzards make it impossible to see. The blowing snow stings when it hits the face. On overcast days, the sky, snow, and ice are the same white color. Explorers can lose all sense of direction and distance.

In the early 1900s, several explorers tried to reach the South Pole. British explorer Ernest Shackleton turned back in 1909 after running out of food. Norwegian explorer Roald Amundson won the race to the South Pole in 1911. He beat British explorer Robert Scott by five weeks. Scott died on the way back from the pole.

A CENTER OF RESEARCH

Today, nearly 30 countries conduct scientific research in Antarctica. Scientists study the ice and the rock beneath the ice to learn about Earth’s history. The ice also tells scientists how Earth’s climate has changed. Scientists study the plants and animals to find out how they can survive in Antarctica’s harsh climate. They also study changes in the fairly clean air over Antarctica to find out how global pollution is affecting Earth’s atmosphere. The United States has the largest Antarctic research center at McMurdo Base.

Arctic

Ice and snow cover the Arctic for most of the year. Winter temperatures drop as low as -90° Fahrenheit (-68° Celsius). On land there are no trees. Only bushes, mosses, and flowers grow in the thin soil. Strangest of all, in the Arctic the Sun doesn’t rise for part of the year!

ARCTIC CIRCLE

Mapmakers like to draw an imaginary line around the top of the globe of Earth. That line is the Arctic Circle. The large region inside the line consists of the Arctic Ocean, many islands, and parts of Asia, Europe, and North America. Outside the circle, the Sun rises and sets every day. That’s not always the case inside the circle.

Winter days are frigid and dark in the Arctic. For weeks, the Sun barely peeks above the horizon. Then it doesn’t rise at all. That’s because Earth is tilted so that the Arctic stays mostly in shadow during winter.

In the southernmost parts of the Arctic, there is only one day when the Sun does not rise. That day is usually December 21. Farther north the Sun doesn’t rise for weeks on end!

The opposite is true in summer. Summer days in the Arctic are cool but bright. The Sun shines almost around the clock. In the southernmost parts of the Arctic the Sun never sets on one day, usually June 21. Farther north the Sun shines all summer!

ARCTIC OCEAN

The surface of the Arctic Ocean is frozen over much of the year. The ice can be 30 feet (9 meters) thick. During the short summers it only partially thaws. Holes in the ice open up, but the ocean ice never completely melts.

The Arctic Ocean is the smallest of the world’s four oceans. The North Pole lies in the middle of the Arctic Ocean.

THE NORTH POLE

You can’t get any farther north than the North Pole. Earth spins around its axis once each day. The axis is another imaginary line that passes through the planet. If you spin a basketball on your finger, the ball’s axis is the line pointing up from your finger through the middle of the ball. The North Pole is one end of Earth’s axis, and the South Pole is the other end.

Admiral Robert E. Peary, an American explorer, was the first person to reach the North Pole. He and five companions reached the pole on April 6, 1909.

DOES ANYONE LIVE IN THE ARCTIC?

People have lived in the Arctic for thousands of years. The Inuit people, who are often called Eskimos, live in northern Alaska and northern Canada. They are believed to be the descendants of people who came from Asia thousands of years ago. Some Inuit once lived in ice houses, or igloos, during winters, and hunted seals, walrus, and polar bears.

Parts of the United States, Canada, Greenland, Norway, Sweden, Denmark, and Russia are in the Arctic. Several large cities lie in the southern portion of the Arctic.

WILDLIFE

You might think the cold would keep animals away, but the Arctic has a lot of wildlife. The world’s biggest bear, the polar bear, lives there. These huge white bears are the only bears that spend a lot of time in the water.

Walruses, whales, seals, and fish live in the Arctic Ocean. Seals are a favorite food of polar bears.

A large number of animals live on land in the Arctic. Among them are foxes, wolves, and reindeer.

Birds flock to the Arctic in spring and summer. Ravens, snowy owls, gulls, and ducks are some of the more familiar ones. Many of the birds flee before the harsh winter sets in. They fly south to warmer lands. This flying back and forth in different seasons is called migrating. Some birds migrate as far south as Mexico and Central America.

Insects such as bees, mosquitoes, and butterflies live in the Arctic, too. Woolly bear caterpillars have an advantage over the other Arctic insects. Woolly bear caterpillars don’t die when they freeze. They can be frozen solid all winter and still crawl away when they thaw out in spring!

Alaska

Alaska is the northernmost state in the United States. It is often called The Land of the Midnight Sun. Because the state is so far north, you can still see the sun at midnight in summer. In winter, darkness lasts much of the day. Alaska has cold winters, but summers in most parts of the state are pleasant and mild.

Alaska is the largest state in the Union. It is more than twice the size of Texas. Alaska also has the highest mountain in the United States. Mount McKinley rises 20,320 feet (6,194 meters) above sea level. Native Americans call this mountain Denali, which means “The High One.”

Alaska is a rugged, wild, and beautiful land. It has majestic mountains and deep fjords (narrow inlets on the coast), slow-moving glaciers, and active volcanoes. Dense forests cover some of Alaska; other parts are treeless and without much plant life. You can take a dip in hot springs or in an icy stream. Alaska is a land of contrasts.

Facts About Alaska

Capital	Juneau
Population	664,000 people
Rank among states in population	47th
Major cities	Anchorage, Juneau, Fairbanks
Area	663,000 square miles 1,720,000 square kilometers
Rank among states in area	1st
Statehood	January 3, 1959, the 49th state
State nickname	The Last Frontier
Name for residents	Alaskans
State bird	Willow Ptarmigan
State flower	Forget-Me-Not
State tree	Sitka Spruce
Abbreviation	AK

THE FIRST AMERICANS

Over 10,000 years ago, the first Americans crossed a land bridge from Asia to Alaska. The people gradually spread out along the coast of Alaska. Eventually, the oceans rose and the Bering Sea covered the land bridge.

Alaska’s native peoples—the Inuit and Aleuts—are related to these first Americans. The state’s name comes from an Aleut word, Alyeska, which means “great land.”

Many Inuit (Eskimos) follow practices of long tradition. They travel by dogsled and kayak. They hunt seals, whales, caribou, and other animals for food. They use sealskins to make clothing and summer tents. The Inuit respect the animals they hunt. After killing an animal, they perform special ceremonies to honor the animal’s spirit. Alaska’s Inuit used to build igloos as shelters on hunting trips. But they do not live in igloos.

RUSSIAN FUR TRADERS

In the 1700s, Russia’s tsar (ruler) heard there was a land east of Russia that was rich in furs. He sent an explorer to look for it. The explorer, Vitus Bering, found Alaska in 1741.

The Russians began to set up fur-trading posts and forts along Alaska’s coast. This made the Tlingit Native Americans angry. In 1802, they destroyed Sitka, a Russian settlement in Alaska.

SEWARD’S FOLLY

Tlingit resistance and money problems at home made Russia decide to sell Alaska to the United States. William Seward, the U.S. secretary of state, reached an agreement with Russia in 1867. The United States purchased Alaska for $7.2 million. Some newspapers called the purchase “Seward’s Folly.” A folly is a foolish act.

The purchase of Alaska did not turn out to be a foolish act. The territory became increasingly valuable to the United States. On January 3, 1959, Alaska became the 49th state. Juneau is the capital. Anchorage is the largest city.

GOLD RUSHES

After the Russian fur traders, the next migration to Alaska came with gold rushes. Gold was discovered near Juneau in 1880. Miners later found gold in Nome and other places. By the summer of 1900, more than 20,000 miners lived in tents in downtown Nome. In 1902, Fairbanks was founded as a result of gold discoveries nearby.

OIL DEPOSITS

Large oil deposits were discovered in 1968 at frozen Prudhoe Bay in northern Alaska. In the 1970s, a long pipeline was built to carry oil from Prudhoe Bay to the ice-free port of Valdez in southern Alaska.

Oil has brought wealth and more people to Alaska, but it has also brought problems. In 1989, an oil tanker hit a reef near Valdez. The tanker spilled millions of gallons of oil into Alaskan waters. The oil killed thousands of birds and sea mammals such as seals and sea otters.

DOGSLEDS AND THE IDITAROD

In the winter of 1925, a disease called diphtheria struck many children in Nome. The children needed a special medicine called a serum to survive. The nearest serum was in Anchorage.

The fastest way to get the serum to Nome was by dogsled. A group of courageous dogsled drivers (called “mushers”) and dogs carried the serum 700 miles (1,100 kilometers) across frozen land in the dark of winter. Nome was saved!

Each year in March, dogsled teams race from Anchorage to Nome to celebrate this event. The event is called the Iditarod. The name of the event comes from the town of Iditarod located halfway between Nome and Anchorage.

ALASKA’S FLAG

Did you know that Alaska’s flag was designed by a 13-year-old boy? John Ben “Benny” Benson created the design in 1927 for a flag contest. Benson was living in an orphanage at the time. The flag features the Big Dipper and the North Star against a deep blue background. The North Star stands for Alaska. What would you put on a flag to represent your state?

Himalayas

The name Himalaya means “home of snow” in the ancient language of Sanskrit. It’s a fitting name. The Himalayas are the highest mountains on Earth. Snow and ice cover much of this impressive mountain range year round.

WHERE ARE THE HIMALAYAS?

The Himalayas rise in southern Asia—the world’s biggest continent. They form a chain that stretches nearly 1,600 miles (2,600 kilometers). The mountains separate the plains of northern India from the high plateau of Tibet, in China.

WORLD’S HIGHEST PEAKS

The Himalayas contain nine of the world’s ten highest peaks. One of these, Mount Everest, is the highest mountain on Earth. It rises to a height of 29,035 feet (8,850 meters).

The world’s second highest mountain, K2 (also called Mount Godwin Austen), also stands in the Himalayas. So does the world’s third highest peak, Mount Kanchenjunga. Other noted Himalayan peaks include Dhaulagiri, Nanga Parbat, and Annapurna 1.

The rugged Himalayas lure mountain climbers and tourists from around the world. The steep mountain slopes are very dangerous. Many climbers have died trying to reach the top of Mount Everest and other Himalayan peaks.

THREE ZONES

The Himalayan range is made up of three mountain zones that run side by side. The highest zone is to the north. It’s called the Great Himalayas, and it holds many of the Himalayas’ tallest peaks, including Mount Everest.

The Himalayas form a great natural barrier. The high mountains are difficult to cross. There are few developed roads, and many trails are open only during summer months. Some parts of the range are up to 250 miles (400 kilometers) wide!

LIFE ON TOP OF THE WORLD

Several kinds of animals live or travel high on the mountains, where only shrubs and grasses grow. They include the snow leopard, which hunts wild goats, and the yak. A yak is a large, long-haired ox. Some Himalayan people keep yaks as pack animals and for their milk and meat.

According to ancient legend, a beast called the Abominable Snowman, or Yeti, lives high on the slopes of the Himalayas. But no proof of the creature’s existence has been found.

The lower slopes of the Himalayas are home to animals such as deer, wolves, and the Himalayan black bear. Tigers, leopards, rhinoceroses, and elephants once lived in the forested foothills. However, people have cut down many of the lowland forests for timber and farmland, and few of these large animals remain.

Most of the people who live in the Himalayas settle in high valleys. There they farm and graze animals. Some Himalayan people, such as the Sherpa of Nepal, serve as guides for mountaineers and tourists.

Aristotle

What is the universe made of? Why do accidents happen? How do animals grow? Ancient Greek philosopher Aristotle tried to find answers to big questions like these. Today, he is remembered as one of the greatest philosophers who ever lived.

WALKING AND TALKING

Aristotle was born in 384 bc in ancient Macedonia (now northern Greece). His father was a doctor. When Aristotle was 17, he went to Athens, the biggest and richest city in ancient Greece. He stayed there for most of his life, studying and teaching. He set up his own school, where students discussed new ideas while strolling in the gardens.

From 345 to 335 bc, Aristotle lived in Macedonia. He worked as tutor to Prince Alexander, who later became known as Alexander the Great. In 335 bc, Aristotle returned to Athens. In 323 bc, Alexander died, and his friends became unpopular. Aristotle was forced to leave his school in Athens. He died the next year, in 322 bc.

INVESTIGATIONS

Aristotle studied many subjects. But he was most interested in science, especially biology (the study of all living things), zoology (the study of animals), and astronomy (the study of the universe). He tried to find out how humans think, and how they experience the world around them. He also tried to describe invisible things, such as the mind and the soul. He invented a new science, called causality. It explained why things happen.

WHAT WAS SO SPECIAL ABOUT ARISTOTLE?

In all his investigations, Aristotle pioneered a new way of studying. He looked for clues in what he saw and for proof. He didn’t use guesswork or accept whatever people already believed. His method of questioning changed the way scholars worked for many centuries.

Aristotle wrote many books, and he kept notes to help teach his students. These might easily have been lost after ancient Greek civilization collapsed. But Muslim scientists carefully preserved these writings and passed them on to scholars in Europe and Asia. Aristotle’s ideas spread around the world.

Plato

Plato was a very original thinker who lived in ancient Greece. He asked questions that nobody had asked before. He even tried to explain how the human mind works.

THE ACADEMY

Plato was born about 428 bc in Athens, Greece. He became a pupil of Greek philosopher Socrates. Then he set up a school in 387 bc. He called his school the Academy. Pupils studied astronomy, biology, mathematics, politics, and philosophy at the Academy.

Plato wrote dialogues—debates that he imagined taking place between teachers and pupils. He hoped these dialogues would help students understand his ideas.

HOW DO WE KNOW?

Plato investigated many topics, from friendship to the heavens. But his most important work was a study of knowledge.

Plato believed that we learn about the world in two different ways. We get useful information through our senses, like sight and touch. But we reach truth by using a higher ability, which he called reason.

Plato said that our senses give us imperfect knowledge, because they tell us about specific objects. But our reason gives us truth, or perfect knowledge, because it tells us about ideas.

GOOD GOVERNMENT

Plato also studied politics and government. He believed that the best government has a philosopher in charge. The minds of philosophers are trained to use reason and understand ideas. According to Plato, the knowledge they gain this way would help them govern wisely and create the best conditions for the people they rule.

After many years at the Academy, Plato wanted to test his beliefs. In 367 bc, he went to Syracuse on the island of Sicily, off the coast of Italy. He went there to teach the new ruler of Syracuse to be a philosopher. But he failed in this effort. Plato returned to write and study in Athens. He died at the age of 80 in 347 bc.

Socrates

What is love? What is truth? What is justice? Socrates, a philosopher in ancient Greece, asked big questions like these and tried to make people think.

Socrates was born in Athens, Greece, in 469 bc. He devoted his life to philosophy. He taught students, made speeches, and debated with anyone who would listen to him.

KNOWING WHAT TO DO

Socrates wanted to find out the best way to live. He wondered why some people behaved well and others behaved badly. He thought that bad behavior resulted from ignorance. He believed that once people knew what was right, they would choose to behave well. Behaving well, Socrates claimed, was the best way to live.

ASKING QUESTIONS

Socrates’ beliefs made him urge fellow citizens to think hard about what they were doing. Was it right? Was it honest? Was it permitted by law? Through questions like these, he hoped to help people recognize their mistakes. This knowledge would bring them closer to the truth and help them lead better lives.

SOCRATES ON TRIAL

Socrates believed it was his duty to ask questions constantly. He thought his method of discussing and debating would help the people of Athens gain knowledge about themselves and their society.

But the government of Athens did not agree. They accused Socrates of corrupting (damaging) young peoples’ minds by inviting them to question and disagree. They said he ignored the Greek gods. In 399 bc, they put Socrates on trial.

Socrates defended his actions. But the jury found him guilty and sentenced him to death.

DOING THE RIGHT THING

Socrates’ friends wanted to help him escape. But Socrates felt that obeying the court’s decision was the right thing to do. Socrates spent his last day with his friends. Then, he calmly drank poison made from a hemlock plant and died.

Socrates wrote no books. But his student Plato admired Socrates so much that he described Socrates’ life and ideas in his own writings.

Adolf Hitler

Adolf Hitler was a struggling young artist who became a feared dictator. He led his country into a bloody war that killed millions of people.

Hitler rose to power in Germany in the 1930s. He eventually started World War II (1939-1945), a conflict that left Europe in ruins.

HITLER’S CHILDHOOD

Adolf Hitler was born in 1889. He came from a well-to-do family in Austria-Hungary. His father was an important government worker. After his father died, Hitler quit school in the ninth grade. He decided to become an artist but had trouble finding work.

WORLD WAR I

Hilter volunteered for the German army during World War I (1914-1918) and served the whole war. Germany lost the war, and the country suffered terribly. Many Germans became jobless and poor. The people wanted someone to lead them back to glory again. Hitler wanted to be that person.

RISE TO POWER

After the war, Hitler joined the National German Socialists Workers’ Party. Many people called it the Nazi Party, for short. Hitler was an excellent public speaker. He appealed to German pride by constantly speaking about their racial superiority. This was the idea that one type of people are naturally better than others. He blamed other people, especially Jews, for Germany’s problems. His speeches attracted thousands of people who thought Hitler could be a great leader. The Nazi Party grew rapidly.

Hitler ran for political office in Germany and was elected in 1930. Three years later, in January 1933, Hitler became Germany’s chancellor, which was similar to a president. He immediately passed laws giving himself total power. Soon, Hitler had become a dictator. He controlled Germany’s government completely.

Hitler passed laws to get rid of people he did not like. They included his political enemies and Germans who were disabled or Jewish. Many of these people were sent to large camps, where they were held prisoner. Huge numbers of people were killed.

WORLD WAR II

Hitler also began rebuilding Germany’s military. He wanted a powerful army so he could conquer other countries, and eventually take over the world. He started by declaring Germany's union with the neighboring country of Austria. Then he ordered German troops to occupy all of Czechoslovakia. When Hitler’s army invaded Poland in 1939, Great Britain and France declared war on Germany. World War II had begun.

Germany’s mighty army soon captured France and began bombing England. In 1941, Hitler’s armies also invaded the Union of Soviet Socialist Republics (USSR), often called Russia. This turned out to be a big mistake because the German army had trouble fighting in several countries at once.

THE HOLOCAUST

Hitler’s soldiers forced tens of thousands of Jews in Poland into small sections of the cities, known as ghettos. The Jews were not given adequate food, and many of them starved to death. Hitler’s army also sent millions of Jews from Germany and other countries to concentration camps. There, many were killed. The deaths of millions of Jews under Hitler is known as the Holocaust. About one-third of the world’s 18 million Jews died in the Holocaust, one of history’s greatest tragedies.

HITLER’S SUICIDE

The United States entered World War II in December 1941. Slowly, Germany began to lose the war. America and its allies launched the D-Day invasion of western Europe on June 6, 1944. They fought their way through France and into Germany in 1945. Facing defeat, Hitler killed himself. His reign of terror was finally over.

Christopher Columbus

Christopher Columbus tried to take a shortcut, and ended up somewhere he never intended to go. He discovered two continents that people in Europe didn’t even know existed. By crossing the Atlantic Ocean in 1492, Columbus opened contacts between lands and peoples that were unknown to each other.

Columbus’s voyage to the Americas opened an exciting period in history. Animals, plants, and new ideas were exchanged between continents. But it also caused terrible tragedy. Millions of Native Americans died as Europeans rushed to take land and riches for themselves.

MASTER SAILOR

Christopher Columbus was born in 1451 in Genoa, Italy. He became a sailor at the age of 14. In 1476, he was shipwrecked off the coast of Portugal. Portugal was Europe’s top seafaring nation at that time. Columbus settled there.

Columbus studied geography and navigation, the science of figuring out where things are on Earth’s surface. He became a master sailor. He met explorers who had sailed along the coast of Africa seeking an eastward sea route to the rich lands of Asia. Europeans called these lands “the Indies.” Europeans wanted to bring gold and other treasures from the Indies back to Europe.

DARING DREAM

Columbus began to think about a wonderful adventure, which he called the “Enterprise of the Indies.” He dreamed of reaching the Indies by sailing west! This was not a new idea, but no one had ever managed to make the voyage. Columbus thought the trip to the Indies west across the ocean would be much shorter than sailing around Africa.

Columbus had high hopes, but no money. Who would pay for his expedition? He asked the king of Portugal, but the king refused. Columbus didn’t give up. He went to the rulers of Portugal’s neighbor, Spain. At first they also refused. Eventually, however, the Spanish king and queen agreed to provide three small ships—the Pinta, the Niña, and the Santa María. They also paid for crews and supplies for the voyage.

HISTORIC VOYAGE

Columbus sailed from Palos, Spain, on August 3, 1492. He stopped at the Canary Islands southwest of Spain, then headed west into unknown seas. He had no idea what lay ahead, but he had faith in his sailing skills and his bold idea. A swift current carried his ships along, and on October 12, the crew sighted the islands of the Bahamas. Columbus thought he had reached Asia. He called the islands the Indies.

Columbus was greeted by the Arawak people who lived on the islands. They offered food, but had only a little gold. Columbus was disappointed not to find Asian treasures, but still felt sure he had reached Japan in Asia. He spent two months exploring, then headed home. One of his ships sank in a storm, but back in Spain he was hailed as a hero. The king and queen offered rich rewards and made him “Admiral of the Ocean Seas.”

THREE FAILURES

Columbus made three more voyages to America. None went well. He was a skillful sailor, but his greed and stubbornness made him a bad leader and created enemies.

During his second voyage (1493-1496), Columbus claimed land for Spanish settlements. He fought against Caribbean peoples who lived on the land he claimed and forced them to work as slaves.

On the third voyage (1498-1500), Columbus quarreled with Spanish settlers so violently that he was sent back to Europe as a prisoner in chains.

On his fourth and final voyage (1502-1504), Columbus was marooned on an island for more than a year. He had to be rescued. He was very ill by the time he returned home to Spain.

AN EXTRAORDINARY EXPLORER

Columbus died in 1506. He quarreled with the king and queen right up until his death. He wanted authority over Spanish colonies and a larger share of the riches that were brought back from America. It was a sad end to an extraordinary career that still shapes our lives today. When Columbus crossed the Atlantic, he changed the world forever.

Ferdinand Magellan

Ferdinand Magellan tried to accomplish something that many people believed was impossible: reach the East by sailing west.

The expedition Magellan led was the first to sail all the way around the world. Magellan’s voyage provided undeniable proof that the Earth was round!

EARLY LIFE

Ferdinand Magellan was born about 1480 in Portugal. He first went to sea in 1505. Magellan joined the Portuguese fleet and served in India, Malaysia, and Indonesia. At that time, these lands were known as the East Indies. Portugal wanted to conquer all of the East Indies to control the international spice trade.

In 1513, Magellan fought against Morocco in northern Africa. He was wounded in the fighting and won a promotion. But the king of Portugal refused to approve Magellan’s promotion.

PLANS FOR A VOYAGE

Magellan then approached the Portuguese king with a plan for a voyage. Magellan believed he could reach the East Indies by sailing west from Europe. No one had ever tried this before. Many said it could not be done. The king denied Magellan’s request for a fleet.

Magellan was angry. He gave up his Portuguese citizenship and moved to Spain. The Portuguese called him a traitor, but Magellan would not turn back.

Magellan knew that Spain, like Portugal, wanted to conquer more lands in the East. In 1517, he asked the king of Spain to finance a westbound voyage. The king agreed, and he even offered Magellan a share in the profits!

THE VOYAGE BEGINS

Magellan outfitted five small ships and prepared to depart. In September 1519, the ships set sail west across the Atlantic Ocean. By April 1520, they reached Argentina in South America. One ship was wrecked in a storm. Many men mutinied, but Magellan put the uprising down.

In August 1520, Magellan’s four remaining ships headed south, into the unknown. One crew panicked and turned back to Spain. But the others sailed on.

DISCOVERY OF A PASSAGE

Magellan’s ships entered a channel near the stormy tip of South America. The channel was narrow and dangerously winding in places. More than five weeks later, the ships finally entered a calm, blue sea. Magellan named this ocean the Pacific, which means “peaceful.” Today, the difficult passage Magellan found bears his name: the Strait of Magellan.

MAGELLAN CROSSES THE PACIFIC

Magellan urged his ships onward to the west. But Magellan had no idea how vast this ocean was. Far from land, the sailors ran out of food. Magellan’s starving men ate rats, leather, and sawdust. Most developed a disease called scurvy, and many died.

After 98 terrible days at sea, Magellan reached the island of Guam. After resting, he sailed on, reaching the Philippines.

MAGELLAN’S DEATH

Magellan made friends with local Philippine leaders. He converted some of them to Christianity. But Magellan also got involved in a rivalry between two chiefs. On April 27, 1521, he was killed in a battle.

Just one of Magellan’s five ships made it back home to Spain. Magellan’s expedition brought Spain little wealth. The route was too long and difficult to be profitable. But the voyage Magellan undertook proved to all that it was possible to sail around the world.

James Cook

Captain James Cook was one of the world’s greatest explorers. He sailed around the world twice. He was the first European to reach Hawaii and New Zealand, and he sailed farther south than any European had ever gone.

People marvelled over the places, people, and things Cook described. Before Cook, nobody in Europe knew about penguins or kangaroos!

EARLY LIFE

Cook was born in 1728 on a farm in northern England. At the age of 18, he went to work for a shipping company. In 1755, Cook joined the British Royal Navy. His ship was sent to Canada, to make maps of land that Britain had conquered from France.

FIRST VOYAGE TO THE PACIFIC

In 1768, Cook sailed to the South Pacific Ocean, with artists and scientists. Officially, their task was to observe the planet Venus. But Britain also hoped that Cook would find a mysterious “Southern Continent” that some sailors claimed to have seen. Cook wanted to take control of it for the British king.

Cook reached New Zealand in 1770. No other European had been there. He sailed around New Zealand and then explored eastern Australia.

A SCIENTIFIC EXPLORER

Cook drew many detailed maps and kept careful records of all he had seen on his voyage. He described native peoples of the South Pacific and their cultures. His artists sketched wildlife, and his scientists collected unusual plants and animals to take back.

Cook’s careful work caused a sensation when he arrived home in Britain in 1771. No other expedition had gathered so much information, so thoroughly and scientifically.

Cook also won fame for keeping his sailors healthy. He wondered if a lack of fresh fruits and vegetables caused scurvy, a fatal disease common among sailors on long voyages. He stocked his ship with sauerkraut (pickled cabbage) and forced his crew to eat it. During stops at port, he ordered his crew to eat fresh foods. As a result, few of his sailors became seriously ill.

SECOND VOYAGE TO THE PACIFIC

From 1772 to 1775, Cook made a second voyage to the South Pacific Ocean. This time, he sailed farther south than anyone before him. He saw penguins and icebergs. He sailed all the way around Antarctica. But he found no land where people might live.

FINAL VOYAGE

In 1776, Cook set off on a third voyage. This time, Cook wanted to look for the Northwest Passage. This was a possible sea route north of Canada linking Europe and Asia. Before sailing north, he explored several islands in the Pacific. He landed in Hawaii in 1778, becoming the first European to do so.

From Hawaii, Cook sailed to North America. He was the first European to set foot on Vancouver Island off the coast of British Columbia. Throughout 1778 he explored the northwest coast of North America, but he failed to find the Northwest Passage. In 1779, Cook returned to Hawaii, where he was killed in a quarrel with natives over a stolen boat.

Marco Polo

They called him “the man with a million stories.” People flocked to Marco Polo’s home to hear him tell exciting tales about his travels in distant lands.

Marco Polo won fame for his journeys across Asia. He wrote a book about his travels that became one of the most famous travel guides in history.

EARLY LIFE

Marco Polo was born in 1254 to a family of merchants. His home was Venice, Italy. Venetian merchants bought and sold valuable Chinese goods, including precious silk cloth. Such goods were brought to Europe along an ancient route known as the Silk Road. The merchants also used the route to travel east on trading missions.

Marco’s mother died when he was a young boy. His family taught him to be a merchant. He learned how to read, write, calculate, and use foreign money.

In 1269, Marco’s father and uncle, Niccolò and Maffeo, returned to Venice after visiting China. In China, they had met the Mongol conqueror Kublai Khan. The khan invited the Polos to return. He asked them to bring Christian scholars to explain the Christian religion to him.

TRIP TO CHINA

In 1271, Niccolò and Maffeo set out for China again. Marco, then 17 years old, joined his father and uncle for the trip. Two priests also traveled with the Polos. But the route was dangerous, and the priests soon turned back.

It took the Polos four difficult years to reach China. The journey led across deserts and high mountains. They passed through wild countryside where bandits lurked, ready to rob and kill. They braved heat and cold, floods, deep snowdrifts, and blinding sandstorms. At last they reached the summer palace of Kublai Khan at Shangdu.

The khan welcomed the Polos warmly. He offered Marco a job. Marco accepted, and the Polos lived in China for the next 17 years. Marco traveled on many special missions across the khan’s kingdom and to distant lands. When Marco returned from his missions, he told the khan vivid stories about the people and lands he visited.

Over time, the Polos worried that Kublai Khan would not allow them to leave. Several times they had asked the khan for permission to return to Europe. But the khan enjoyed his visitors so much that he would not grant their wish. Finally, the khan changed his mind.

RETURN TO VENICE

In 1292, Kublai Khan asked Marco to escort a Mongol princess to Persia. The Polos traveled by ship from China to the Persian Gulf. Then the Polos headed for Venice, finally reaching home in 1295. Marco had been away so long that nobody recognized him!

We know about Marco’s travels because, in 1298, he became a prisoner of war. He shared his cell with a writer named Rustichello, who helped Marco turn his stories into a book. Rustichello added some details of his own. But much of Marco’s book seems to be true!

Marco Polo returned to Venice after his release from prison. He died in 1324. But his book remained popular for centuries. Merchants, mapmakers, and explorers all looked to the book for information about Asian lands. Even the navigator Christopher Columbus owned a copy!

Mohandas Gandhi

Many people consider Mohandas Gandhi the greatest figure of the 20th century. Gandhi freed India from rule by the British Empire. But it was how Gandhi did it that won the world’s respect. Most new nations are born through war. Gandhi found a different way. He was against violence.

GANDHI’S EARLY LIFE

Mohandas K. Gandhi was born in India in 1869. India had then been ruled by Britain for a century. At his mother’s urging, Mohandas went to college in England and studied law.

In 1893, Gandhi went to South Africa to practice law. South Africa, too, was then part of the British Empire. It had a large Indian community. Gandhi was angry to find that Indians were denied basic freedoms. In 1896, he began to lead Indians in South Africa in a struggle for equal rights.

It was not an armed struggle. Gandhi preached nonviolence. He organized marches to call attention to his cause. His followers refused to obey unfair laws. When attacked by police, they did not fight back.

Gandhi described his policy by an Indian word that meant “truth and firmness.” He was jailed many times. But his courage won people to his cause. In 1914, the South African government granted Indians their rights.

GANDHI IN INDIA

Gandhi returned to India in 1915. His goal was to win for his country the right to rule itself. His methods of strong but peaceful resistance spread across India.

In 1920, British soldiers killed hundreds of peaceful protesters in the city of Amritsar. Gandhi then called on Indians to refuse to cooperate with Britain. People stopped buying British goods. Instead, they made things at home in traditional ways. They took their children out of British schools. Those in government jobs quit.

During the years of resistance, Gandhi lived the simple life of the poorest Indians. He gave away his possessions. People called him Mahatma, meaning “great soul.” It was a title given to wise religious leaders.

BRINGING CHANGE

Not all Indians followed Gandhi. Sometimes violence erupted against the British. This troubled Gandhi so much that he quit politics several times. But his people’s struggle kept drawing him back in.

In 1930, Gandhi called on Indians to refuse to pay taxes to Britain. The most hated tax was on salt. Gandhi led thousands of followers on a march to the sea to make salt from seawater. He was arrested again. But a year later, the British removed the salt tax and freed him. Without Gandhi, the British government realized, India would break out in violent revolution.

Gandhi also tried to break India’s traditional caste (social class) system. He supported the rights of people in the lowest caste, called untouchables. They were the poorest, most oppressed Indians.

Religion also divided India’s people. Violence sometimes broke out between Hindus and Muslims. Gandhi tried to bring them together.

“YOU MUST BE THE CHANGE”

In 1939, World War II began. Gandhi refused to support Britain in the war unless India was granted complete independence after it was over. Five years later, the British agreed.

India became a free country in 1947. Gandhi’s dream of a united India was not realized, however. India’s people were mostly Hindus. The country’s Muslims demanded their own state, which became Pakistan. Religious violence broke out between India and Pakistan.

Gandhi himself became a victim of the violence. On January 30, 1948, he was shot and killed by an Indian who hated his efforts to achieve peace.

“You must be the change you wish to see in the world,” Mahatma Gandhi said. His death was considered a world tragedy. But his life inspired other people. One person who followed Gandhi’s way was American civil-rights leader Martin Luther King, Jr.

Muhammad

The prophet Muhammad was a man with a mission—to tell people about God. His teachings founded a new religion, Islam. The followers of Muhammad and Islam are called Muslims. Today, Islam is one of the world's largest religions, with almost 1 billion followers.

THE TRUSTED ONE

Muhammad was born about ad 570 in Mecca, a trading center in Arabia (now Saudi Arabia). Because he was thoughtful and serious by nature, he was called al-Amin. This means “the trusted one” in the Arabic language. Muhammad worked as a merchant, traveling long distances to trade.

THE PROPHET

On his travels, Muhammad met people from many faiths and discussed religious ideas with them. He also took time away from busy, noisy Mecca, to pray and meditate (think deeply) in a cave. While he was there, he experienced religious visions, or revelations. He came to believe he had been chosen as a prophet to preach God’s message to the world.

ONE GOD

Muhammad spoke to the people of Mecca. He told them to destroy their old idols and worship Allah, the one true God. He said God was all-powerful, but loving and merciful. He said that God had sent earlier prophets, such as Moses and Jesus, but that now there wouldn’t be any more.

Muhammad’s preaching won converts but also made enemies. In ad 622 he fled from Mecca to a distant city, Medina, and set up a Muslim community there. After years of fighting, the Muslims from Medina conquered Mecca. Its citizens became Muslims. Quickly, Islam spread through Arabia and beyond.

THE MUSLIM WAY OF LIFE

Muhammad taught Muslims to pray five times a day, give to charity, fast during the month of Ramadan, and go on pilgrimages to Mecca. He told them that all Muslims were equal, whatever their race, class, or color. He said they should live at peace with Jews and Christians because they worshiped the same God.

Muhammad died in ad 632. To guide believers, his revelations were written down in the Qur’an. Muslims believe it is the word of God. Muhammad’s own words were treasured as Hadith (“sayings”), and his way of life was honored as Sunna (“good example”).

Islam

Islam is the second largest religion in the world. Only Christianity has more followers. People who follow the religion of Islam are called Muslims. Today, almost 1 billion people call themselves Muslims. Most Muslims live in a string of countries that extends from Morocco in North Africa to Indonesia in Southeast Asia.

BIRTH OF ISLAM

An Arab trader named Muhammad was the founding prophet of Islam. He lived in Mecca, a busy trading town in Arabia (now called Saudi Arabia). Mecca had temples built to honor various pagan gods. Pilgrims visited these temples to worship statues of the gods. One day, while fasting in a cave, Muhammad had a vision. He returned to Mecca to preach a new religious message. He said there is only one god, not many, and no one should worship idols (statues of gods). He called on the people of Mecca to surrender themselves to Allah, as he called God.

ISLAM GAINS POWER

Muhammad’s message angered some Meccans. In the year 622, they forced him to flee to another city, now known as Medina. That journey—or Hegira, as Muslims call it—marks the beginning of the Islamic calendar. In Medina, Muhammad became the head of the community. Soon, he led his Muslim followers back to Mecca. After a battle, the Meccans accepted Islam. Within a century, Muslims ruled an empire that stretched from India to Spain. Throughout this empire, Islam took root. The empire crumbled after a few centuries, but many people of these lands remained Muslims.

ISLAM DIVIDES

After Muhammad’s death in 632, Muslims disagreed about how the next leader should be chosen. One group came to be known as Sunnis and the other as Shias. Islam remains divided into these two branches.

By the year 900, a Muslim movement called Sufism had developed. Sufis seek a personal experience of God. Many great Muslim poets have been Sufis. Sufis helped to spread Islam long after the Islamic empire crumbled.

WHAT DO MUSLIMS BELIEVE?

The Muslim faith centers on five beliefs and practices. These are known as the five pillars of Islam. According to the five pillars, Muslims must

Accept that only one God exists and Muhammad was his messenger.
Perform certain prayers five times a day.
Fast from dawn to dusk during a month called Ramadan.
Give a portion of their wealth to the poor.
Visit Mecca at least once if they are able to.

These practices are based on the holy book of Islam, the Qur’an (also spelled Koran). Muslims believe that the Qur’an is the word of God, delivered through Muhammad. Muslim practices are also based on the Hadith—Muhammad’s own deeds and sayings as reported by his companions.

ISLAMIC LAWS AND CUSTOMS

In the early Islamic empire, the government and the religion were the same. All questions that came up were decided by religious scholars. Their decisions filled in a set of laws called the Sharia. These laws, which are also drawn from the Qur’an and Hadith, cover every aspect of life. They tell what crimes should be punished and how. They set the rules for marriage, contracts, and inheritance.

Islam is thus a complete way of life. In this way of life, men and women generally have different roles. Their activities are often kept quite separated. Families sometimes arrange marriages. Women are expected to be well covered when they go outdoors. In some countries, they have to wear a veil covering their body. In Arab countries, such a covering is called a burka.

The mosque is the traditional place of worship for Muslims. Friday is their holy day, or day of worship. Islam teaches that all Muslims are equal before God. This teaching gives Muslims around the world a sense of community, no matter what country or social class they come from.

Indonesia

Indonesia is a tropical country made up entirely of islands. How many islands? It’s got more than 13,600 of them! Tigers, pythons, and crocodiles live in thick rain forests that cover some of the islands. Towering mountains and active volcanoes rise across Indonesia, the world’s largest island nation.

People live on about half of Indonesia’s islands. The main islands include Java, Sumatra, and Sulawesi. Thousands of Indonesia’s smaller islands are little more than tiny dots of land. Indonesia also owns parts of the islands of Borneo, New Guinea, and Timor. Many Indonesians use boats for fishing and traveling between the islands.

Facts About Indonesia

Official name	Republic of Indonesia
Capital	Jakarta
Official language	Bahasa Indonesia
Population	245,000,000 people
Rank among countries in population	4th
Major cities	Jakarta, Bandung, Surabaya
Area	735,000 square miles 1,900,000 square kilometers
Rank among countries in area	15th
Highest point	Mt. Jaya 16,503 feet/5,030 meters
Currency	Indonesian rupiah

WHERE IS INDONESIA?

The Indonesian islands lie near the equator, the imaginary line that encircles Earth around its middle. They stretch for thousands of miles, from the Malay Peninsula almost to Australia. The islands form a chain that separates the Indian and Pacific oceans.

PEOPLE OF INDONESIA

For centuries, traders sailing between India and China had to pass through Indonesian waters. Most traders sailed through the Straits of Malacca, a narrow waterway between Sumatra and Malaysia. Over time, many different people settled in Indonesia. The islands have many native tribes, too. Today, about 300 different languages are spoken across Indonesia.

Indonesia is the world’s fourth most populous country, after China, India, and the United States. Some Indonesian islands are very crowded. More than half of Indonesia’s 245 million people live on just one island, Java. Java covers an area about the size of New York state. Jakarta, Indonesia’s capital and largest city, is located on Java.

TROPICAL WEATHER

Indonesia is in the tropics, so the climate is hot and humid all year round. Instead of hot and cold seasons, Indonesia has wet seasons and dry seasons.

Winds called monsoons cause Indonesia’s wet and dry seasons. From November through March, the winds carry heavy rains to Indonesia. From June to October, the winds bring dry air to the islands.

MOUNTAINS AND VOLCANOES

Mountains and volcanoes cover much of Indonesia. In fact, Indonesia has more volcanoes than any other place in the world. Volcanoes rise on all the major islands except Borneo and New Guinea. A volcano erupts somewhere in Indonesia at least once a year.

Many Indonesian people live near volcanoes. That’s because volcanic ash (dust that falls from the air after an eruption) makes the soil good for farming. When volcanoes erupt, they can kill many people.

KRAKATAU

One of the worst volcanic eruptions in history occurred in Indonesia. In 1883, a volcano blew up the island of Krakatau. The eruption caused huge tsunamis (tidal waves) that killed thousands of people. The explosion made one of history’s loudest noises. It could be heard 3,000 miles (4,800 kilometers) away!

UNUSUAL ANIMALS

Wildlife flourishes in Indonesia, especially on islands where few people live. Indonesia is home to many rare animals, including rhinoceroses, elephants, and dwarf buffaloes. Brightly colored parrots, parakeets, and birds of paradise can be seen in the tropical forests.

The dangerous Komodo dragon, the world’s largest lizard, lives only on several small Indonesian islands, including the island of Komodo. It can grow more than 10 feet (3 meters) long and weigh 365 pounds (165 kilograms)!

Another rare animal found only in Indonesia is an ape called the orangutan. The name orangutan means “man of the jungle” in the Malay language. Orangutans spend most of their time in trees. Today, orangutans are endangered because Indonesian loggers have cut down so much of the tropical forest.

THE SPICE ISLANDS

Long ago, Indonesia was famous for its spices. Part of Indonesia was known as the Spice Islands. The people of Europe greatly prized the spices of Indonesia. Merchants carried the spices back to Europe, where black pepper was more valuable than gold!

Europeans fought over Indonesia throughout the 1500s and early 1600s. The Dutch eventually won, and they took control of Indonesia. The Dutch forced Indonesian people to grow spices and other valuable crops, and they took all the wealth back to Europe. Indonesia did not gain its freedom until 1949.

CUSTOMS OF INDONESIA

Rice is the main food of Indonesians. Rice is grown throughout Indonesia, and it is usually eaten at every meal. Black tea is a popular beverage.

One of Indonesia’s best-known arts is called batik. It’s a method of dyeing cloth to make beautiful patterns. Batik is cloth painted with melted wax and then dyed. The waxed areas do not absorb the dye. When the wax is removed, the patterns remain.

Puppet shows are another famous art form of Indonesia. The puppets are usually made from wood or leather. Yet the audience never sees the puppets. The puppeteer moves the puppets behind a white screen to act out a story. The audience sits on the other side. It sees only the shadows of the puppets on the screen.

HINDUISM AND ISLAM

The shadow puppet plays often tell stories from Hindu poems. The people of Bali, a small Indonesian island, follow a form of Hinduism. Hinduism is a religion that came to Bali from India. Hinduism has greatly influenced the culture of Indonesia.

Yet most Indonesians are not Hindus. They are Muslims, or followers of Islam. In fact, nearly 90 percent of Indonesians are Muslim. That makes Indonesia the largest Muslim country in the world.

Pioneer Life

Frontier lands to the west beckoned American pioneers. Send your strongest people! Deliver your bravest souls! Come, test yourself—can you survive on the rugged, wild frontier?

From the early 1700s to the late 1800s, thousands of American pioneers answered the challenge and moved west. With ax and plow, they settled a vast wilderness. Their hard work and courage pushed the American frontier all the way to the Pacific Ocean.

Frontier life was difficult. Pioneers needed many skills just to survive. Life on the frontier meant living far from neighbors. It meant giving up markets, shops, schools, churches, and even news. Pioneers did without or made what they needed using simple tools.

MOVING WESTWARD

In the 1700s, early pioneers crossed the rugged Appalachian Mountains in the eastern United States. Thick woods and steep valleys made the trip difficult. At first, they traveled on narrow trails. With the help of explorers such as Daniel Boone, roads big enough for wagons were cut through the mountains.

By the mid-1800s, the Great Plains to the west called out to a new wave of pioneers. The plains stretched out beyond the Mississippi River like a treeless ocean of grass. The great Rocky Mountains towered beyond the plains. Beyond the mountains lay the rich lands of the far west.

Adventurous pioneers spread out quickly over western lands. Some were lured by the promise of land for farming, grazing, and timber. Others went in search of valuable minerals such as gold, silver, and copper.

CONFLICT ON THE FRONTIER

The pioneers and Native Americans fought many wars on the frontier. The pioneers built homes and farms on Indian hunting lands. Native Americans then attacked the settlers or raided their settlements.

Some Indians signed treaties giving up their lands. But settlers or Indians often broke the treaties, leading to war. Many died in the fighting. Eventually, Native Americans were driven from most of their lands.

FILLING EMPTY STOMACHS

To survive on the frontier, a pioneer family first had to clear a patch of land for planting crops. They swung sharp axes to cut down trees and clear brush. Heavy wooden plows broke the ground. Farmers scattered seeds by hand. They used handheld sickles to cut ripe grain.

Few trees grew on the Great Plains. But under the soil lay a tangle of deep, thick grass roots that snapped wooden plows. Farmers needed sharp, steel plows to cut through the soil.

Pioneers had to produce enough food in the spring, summer, and fall for winter meals. Families preserved meat and fish with salt and smoke. They dried fruit, beans, and peas. They ground corn into meal for cakes and bread. They made cheese from milk and brewed cider from apples.

This hard work meant survival during the winter months. With no markets to fetch new supplies, pioneers without enough food faced starvation.

As more people moved to the frontier, stores followed. A few times a year, pioneers piled into their farm wagons and made the long trip into town. There they purchased supplies such as sugar and salt.

OH, GIVE ME A HOME

Early pioneers lived surrounded by trees. Many built their homes with logs. Most homes were small, with only one or two rooms. Sometimes, they added an overhead loft reached by a ladder. Many cabins had dirt floors. Packed mud filled the gaps between logs.

Later, when a family had time, they might add a wooden floor. They constructed pens and a barn for their animals. They often built a smokehouse to preserve meat.

On the treeless plains, pioneers cut bricks of grass and soil from the ground. They stacked the bricks into a house. Sometimes, women tacked up cloth to catch dirt that sprinkled down from walls and ceilings. Snakes, mice, and bugs felt right at home in a house made of dirt!

In the dry Southwest, pioneers copied the Native American homes, called pueblos. The pioneers built homes out of adobe, a sun-dried clay.

Pioneers supplied their homes with handmade goods. Men built simple furniture. Boys whittled spoons from wood and carved bowls and platters. Women stuffed mattresses with feathers or cornhusks. Women also made items such as soap for bathing and candles for light.

PROTECTION

Frontier families relied on guns for hunting and protection. Often alone, families needed to protect themselves from danger. Many pioneers lived in constant fear of an attack by Indians.

Until the mid-1800s, most pioneers owned long rifles that fired once, then needed reloading. In 1831, Samuel Colt invented a revolver that shot several bullets before you had to reload. These guns became popular on the frontier.

WHAT TO WEAR?

Frontier clothes took a lot of time to make. They had to last a long time. A woman sewed her family’s clothes. Sometimes, she even made the cloth herself. During the winter months, she spun sheep wool into thread, wove it into fabric on a loom, and dipped it in dye. Then she sewed clothes and knit socks and caps.

Sometimes she could buy, or trade, for a piece of cloth from a store. She sewed scraps of cloth into rugs and bed quilts.

Pioneers adopted Native American clothing, too. They wore deerskin pants, jackets, and moccasins.

FAMILY MEDICINE

Isolated pioneer families relied on themselves for medical care. Women made medicines from herbs, roots, alcohol, and animal grease. Parents set broken bones with stick splints and bandages. Mothers stitched wounds with sewing needles and thread. People drank whiskey to ease pain.

People often didn’t know what caused a disease or how it spread. Many pioneers died of sickness or infected wounds.

TIME FOR SOME FUN!

Pioneers enjoyed gathering with neighbors. They exchanged news, advice, and gossip. Sometimes they’d hold a dance outdoors under the stars. A few fiddles, clapping, and songs like “Skip to My Lou” provided music.

Neighbors gathered to help one another with big jobs, like building a barn. Women baked pies and cooked for days. Then everyone had a big feast. Afterward, they told stories or danced and sang.

Children played with pets, listened to stories, and made their own toys. They played games such as hide-and-seek and blind-man’s-bluff.

Such simple pleasures helped ease the pioneers’ hard work in taming the great American West.

Cowboys

Picture spending your days riding a horse in the great outdoors. During daylight, you tend herds of cattle on vast stretches of open land. At night, you cook your meals over a campfire and sleep under the stars. Such was the life of an American cowboy.

Life as a cowboy may sound exciting and fun. But cowboys spent long hours doing hard, often dangerous, work. It could also be very lonely out on the range, even downright boring!

WHAT IS A COWBOY?

A cowboy is a ranch worker who rides on horseback to herd cows. Cowboys won fame on the Western frontier for their endurance and independent way of life. The first cowboys worked on Spanish ranches in California in the 1600s.

THE AGE OF COWBOYS

The best-known cowboy period began after the American Civil War ended in 1865. It lasted through the 1890s. At that time, millions of wild cows roamed the unfenced Western plains. As the American population grew, more and more people wanted beef to eat.

When the war ended, thousands of jobless soldiers needed work. Cattle ranchers saw this as a chance to make money. They hired men to round up the wild cows for them.

The wild cows were known as Texas longhorns, because large numbers of these long-horned animals roamed the Texas plains. Texas longhorns were descended from Spanish cattle that had escaped and multiplied on the range.

WHAT DID COWBOYS DO?

A cowboy’s main job was to herd cattle to the range to graze. Cowboys also had to protect their herds from outlaws, called rustlers, who wanted to steal cattle. For this reason, many cowboys carried pistols.

A cowboy’s greatest fear was not of outlaws, but of stampedes. A stampede is a charge by a herd of cows in a panic. Anyone in the path of a stampede can get trampled.

Twice a year, in the spring and fall, the roundup took place. During a roundup, all the cattle were brought together so newborn calves could be identified. In the days of the open range, cattle belonging to different owners might get mixed together. For this reason, cowboys burned special marks on the calves with hot irons. These marks, called brands, showed who owned the animals.

An important event in the life of a cowboy was the trail drive. During a drive, cowboys herded the cows to towns that had railroad stations. A trail drive might cover hundreds of miles and last several months. Once the cowboys arrived in town with their herd, the cows were shipped to meatpacking plants in big cities.

A COWBOY’S EQUIPMENT

Cowboys wore clothes that fit their job. Their famous “ten-gallon” hats had big brims to give them shade. They kept kerchiefs, or bandannas, around their necks to shield their mouths from dust.

Cowboys wore tough cotton jeans, called denim. Over their pants they wore leather flaps, or leggings, called chaps. Denim and chaps let cowboys ride through thorny brush. High boots protected their ankles. The long heels of their boots helped keep their feet in the stirrups.

All cowboys carried a rope called a lariat, or lasso. They tied the lariat to their saddles. A cowboy could put a loop in his lariat, whirl it over his head, and catch a cow that had strayed.

COWBOYS TODAY

There are still cowboys working today in parts of the American West. But the old-time cowboy way of life mostly disappeared after fences were built across the Western plains.

Modern cowboys still work hard, wear chaps and boots, and sport large cowboy hats. They must be expert horse riders and know how to use their ropes. But they use many modern machines, including trucks for moving cattle to market and chain saws to cut fence posts.

WHY ARE COWBOYS REMEMBERED?

The cowboys’ independent, hard-working life made them seem like heroes to many. American writers such as Zane Grey and Louis L’Amour wrote novels about courageous cowboys. Countless movies and television shows portray cowboys. Today, in many countries, cowboys are seen as a symbol of America.

Astronauts

“That’s one small step for man, one giant leap for mankind.” Astronaut Neil Armstrong spoke these words on July 20, 1969, as he became the first person ever to step onto the Moon.

An astronaut is a space traveler. Astronauts fly into space on spaceships. They go where there is no air, higher than any airplane can fly. While they orbit (go around) Earth, they are weightless—they float and feel no gravity.

WHO GETS TO BE AN ASTRONAUT?

In Neil Armstrong’s day, all astronauts were military test pilots. Today, they’re as likely to be medical doctors, scientists, or engineers. Astronauts are still pretty unusual, however. Only a few hundred people have ever traveled into space.

Astronauts receive intense training. Then they may prepare a year or more for a specific mission. Pilots must be able to control all spacecraft systems and deal with emergencies. They may need to make course changes or dock with a space station. They must be able to land the spacecraft. Mission specialists are experts on particular experiments. Any astronaut may have to perform duties in a space suit outside the craft.

WHAT DO ASTRONAUTS DO IN SPACE?

Most space missions do not require human passengers. Robots and computers can do many jobs without needing people. But astronauts can perform some experiments in space that machines cannot. They can examine, for example, how flames burn or how crystals grow without gravity. Some experiments test the effects of spaceflight on human beings. Astronauts also launch and repair satellites, machines that orbit Earth. They also retrieve objects in space for return to Earth.

Astronauts may spend weeks or even months in space. Russian cosmonaut Valeriy Polyakov holds the record for the most consecutive days in space. He spent 438 days aboard the Mir Space Station in 1994 and 1995.

THE FIRST ASTRONAUTS

Russian astronauts are called cosmonauts. The first person in space was cosmonaut Yuri Gagarin. He made the trip in April 1961. The first American, a month later, was astronaut Alan Shepard. The first capsules that carried astronauts into space were barely large enough to hold their single passenger.

FLYING TO THE MOON

The Apollo program began during the 1960s. Apollo was an American project to send people to the Moon and back. There were three astronauts in each Apollo crew. Two of them explored the Moon while the third stayed aboard the main spacecraft.

Neil Armstrong, Buzz Aldrin, and Michael Collins were the crew of Apollo 11. This was the first mission to land on the Moon. Altogether, 12 astronauts walked on the Moon as part of the Apollo program. They performed experiments and brought back moon rocks for study. No one else has ever been to the Moon.

THE SPACE SHUTTLE

During the 1980s, the United States began to use space shuttles to send astronauts into space. Previously, spaceships could only fly once. Each trip required a new spaceship. Now, space shuttles can fly into space many times. They are launched from the top of a rocket, but they land like an airplane. Up to seven crew members can live aboard a shuttle.

The United States has begun research on a new type of reusable spaceship to replace the space shuttle. This new spaceship will use newer technology and will be cheaper to operate than the space shuttle. Someday astronauts may walk on the Moon again, or even travel to other planets!

Moon

Did you ever look at the Moon and think you could see a face? Sometimes dark spots on the Moon look like eyes, a nose, and a mouth. People used to talk about “the man in the Moon.” They would joke about the Moon being made of cheese with holes in it.

The Moon is the second brightest thing in our sky, after the Sun. The Moon doesn’t make its own light. Light rays from the Sun bounce off it and make it shine. The Moon is closer to Earth than any other body in our solar system.

WHAT’S ON THE MOON?

In the 1600s, the famous Italian scientist Galileo was the first person to look at the Moon through a telescope. He saw dark spots that he thought were oceans. He called them maria, the Latin word for “seas.” Galileo thought the light areas were large landmasses called continents.

Today, we know a lot more about the Moon. We know that nothing lives on the Moon, and there are no oceans. The maria are dry, flat plains covered with rocks. The Moon is the only place in space that human beings have visited.

TOUCHING THE MOON

The first astronauts landed on the Moon in 1969. They traveled in a United States spacecraft named Apollo 11. The astronauts set up experiments on the Moon and brought some moon rocks back to Earth. Later, five more Apollo missions explored different parts of the Moon. The astronauts on these missions brought back more rocks and soil.

Scientists learned many things about the Moon from the Apollo space missions. They also learned from other spacecraft that orbited (went around) the Moon. Some of these spacecraft sent robot landers down to the surface of the Moon.

SPACE ROCKS AND CRATERS

The dry, gray Moon might seem like a boring place now. But you should have seen it several billion years ago.

Many times over the past two or three billion years, chunks of rock and ice have come whizzing toward the Moon. The space rocks and ice are asteroids and comets. They slam into the Moon’s surface. The biggest ones came just after Earth and the other planets were formed. When they hit the Moon, these large objects threw up tons of rock and dust. There are billions of big and small pits on the Moon made by the space rocks. These pits are called craters.

ANCIENT VOLCANOES

If you went to the Moon, you’d see the dark-colored maria. Scientists think the dark gray rock is lava (melted rock). They believe that billions of years ago, red-hot rock gushed up from volcanoes on the Moon. The lava flowed over the Moon’s surface. It filled in low places, including some of the big craters. Then the lava cooled to make the Moon’s gray rocks.

The lava also left round hills on the Moon called domes and carved grooves called rilles.

ROUGH HIGHLANDS

There are rough and mountainous places all over the Moon. Scientists call these places highlands.

There are highlands on the far side of the Moon but almost no maria. Only one side of the Moon faces Earth, so you can never see the far side of the Moon. Scientists learned what the far side looks like from pictures taken by orbiting spacecraft.

HOT DAYS AND COLD NIGHTS

The astronauts who walked on the Moon had to wear big space suits. The space suits provided air for the astronauts to breathe, because there is no air on the Moon. The suits also kept the astronauts cool during hot Moon days and warm during cold Moon nights.

With no atmosphere to protect it, Moon temperatures can be very high and very low. It can be 261° Fahrenheit (127° Celsius) at noon during a Moon day—hotter than boiling water! It can be as cold as -279° Fahrenheit (-173° Celsius) on a Moon night. Days and nights on the Moon each last about two weeks.

Days and nights are long because the Moon turns very slowly. It takes the Moon about 27 days to make one turn. Earth turns once every 24 hours.

ICE ON THE MOON?

There is no water on the Moon, but scientists think that there may be ice. Two spacecraft in the 1990s saw signs of the ice. If there is ice on the Moon, it could help future explorers stay there longer.

The signs of ice were found in deep craters at the north and south poles of the Moon. Because these craters are always in shadow, it stays very cold there—about -364° Fahrenheit (-220° Celsius).

THE MOON FROM EARTH

The Moon always seems to change shape. Sometimes it looks like a round ball in the sky. Sometimes it is a thin sliver. But the Moon does not really change shape. What happens to it?

The Moon reflects light from the Sun. How you see the reflected sunlight depends on where the Moon is. The Moon orbits (goes around) Earth. Sometimes it is between the Sun and Earth, and you can’t see any reflected sunlight. This is called the new moon.

Sometimes Earth is between the Moon and the Sun. You can see all of the reflected sunlight. The Moon looks round. This is called a full moon.

The rest of the time, you see only part of the reflected sunlight from the Moon. The reflected sunlight looks like slivers of Moon. It takes about 27 days to go from a new moon to a full moon and back to a new moon again.

WHERE THE MOON CAME FROM

No one knows for sure how the Moon was formed. By testing moon rocks, scientists have learned that the Moon is about 4.6 billion years old. This is the same age as the solar system.

Scientists think that at that time something as big as a planet crashed into Earth. The collision blasted huge pieces of Earth into space. Some of the pieces came together to make the Moon.

Scientists continue to study moon rocks for clues. There is still much to learn about the Moon.

Earth

Pretend you are an alien explorer from outer space looking for life on other planets. Your spaceship flies into a group of stars that looks like a gigantic whirlpool. The whirlpool is the Milky Way Galaxy.

You head for a star with nine planets in one arm of the Milky Way. The third planet from the star is a beautiful blue, white, and green ball. This planet looks like it has life. The name of this planet is Earth.

HOW DOES EARTH MOVE IN SPACE?

Earth spins like a top on its axis. Earth’s axis is an imaginary line that goes through Earth from the North Pole to the South Pole. Earth’s axis is slightly tipped, like a spinning top leaning to one side.

Earth travels around the Sun at about 67,000 miles per hour (about 107,000 kilometers per hour). One year is one trip around the Sun. Earth’s path around the Sun is slightly oval-shaped. This oval shape causes Earth’s distance from the Sun to change during the year.

WHAT MAKES DAY AND NIGHT?

The Sun seems to rise in the morning, cross the sky during the day, and set at night. However, the Sun does not actually move around Earth. Earth’s turning on its axis makes it look as if the Sun is moving.

Earth makes a complete turn on its axis every 24 hours. As Earth turns, half of the planet faces the Sun, and the other half faces away. It is daytime on the half facing the Sun. It is night on the half facing away from the Sun.

WHY ARE THERE SEASONS?

Earth has seasons because of the tilt of its axis. For part of the year, the top half of Earth is tipped toward the Sun. The top half of Earth is called the Northern Hemisphere. During another part of the year, the bottom half of Earth is tipped toward the Sun. The bottom half is called the Southern Hemisphere. It is summer in the half that is tipped toward the Sun. It is winter in the half tipped away. When it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere. During spring and fall the hemispheres are tipped neither toward nor away from the Sun.

The equator is an imaginary line around Earth’s middle. The farther you are from the equator, the greater the difference in temperature between seasons. The equator never tips far from the Sun. Near the equator it is warm enough to go swimming all year long. The average temperature barely changes from month to month. In Alaska, far from the equator, the average temperature in January can be more than 60 degrees colder than it is in July.

WHY IS THERE LIFE ON EARTH?

Earth has just the right conditions for life. It is not too hot or too cold. Earth has lots of liquid water and an atmosphere (gases) that can support life.

The first kinds of life may have appeared on Earth 3.8 billion (3,800,000,000) years ago. Several times during Earth’s history, almost all life went extinct, or disappeared. Each time, some life forms survived. The survivors spread all over the planet. Dinosaurs appeared about 230 million years ago. Dinosaurs went extinct about 65 million years ago. Scientists believe that modern humans appeared about 130,000 years ago.

WHAT IS THE INSIDE OF EARTH LIKE?

Earth is made of layers. The top layer is called the crust. It is made of hard rock and soil.

More than 70 percent of Earth’s crust is covered with water. Most of the water is salt water in the ocean. Pieces of dry land called continents rise above the ocean. The part of Earth’s crust under the ocean is called the seafloor.

Under the crust is a layer of partly melted rock called the mantle. Under the mantle is Earth’s core. The core is mostly iron. The outer part of the core is liquid metal. The inside of the core is solid metal. Scientists believe that the liquid metal makes Earth a giant magnet and creates Earth’s magnetic field.

Earth’s crust is made of gigantic slabs of rock called plates that move over the mantle. Plates crash together to make mountains. They pull apart and let red-hot rock ooze up from inside Earth to make new crust.

HOW DID EARTH FORM?

Scientists think that Earth and the rest of the solar system formed from a spinning cloud of gas and dust. Gravity pulled most of the gas and dust together to form the Sun. Some leftover gas and dust formed Earth and the other planets. Scientists think that Earth and the Moon formed about 4.6 billion years ago.

Earthquakes

What could be scarier than feeling the ground shake under your feet? Maybe this has happened if you live in a place that has earthquakes. The furniture shakes. Pictures drop from walls. Books fall off shelves. In really big quakes, roads can crumple up. Buildings and bridges can even collapse. And people can be killed.

WHAT CAUSES AN EARTHQUAKE?

Earthquakes are movements in Earth’s crust. The crust is Earth’s rocky outer layer, the solid ground that we live on. Earth’s crust is broken up into many gigantic sections of rigid rock called plates. The plates slide around slowly on a layer of hot, melted rock deep inside Earth. Sometimes the plates crash together. Sometimes the edge of one plate slides under another plate.

Faults are cracks in Earth’s crust between the huge plates. Earthquakes usually happen along faults. The plates on each side of a fault press against each other with tremendous force. An earthquake occurs when the rock along the edge suddenly gives way. Huge chunks of rock underground break and move. They can jolt upward or they can dive down. Sometimes the blocks of rock along a fault grind sideways past each other.

The place where the rock breaks is called the focus of the earthquake. It is usually underground. The breaking and moving makes waves travel through the ground. The waves go through the ground the way waves go through water. The ground ripples and shakes.

The place on the ground directly above the focus is called the epicenter. Earthquakes are strongest near their epicenters. Earthquake waves go out in big circles. Waves made by a powerful earthquake can travel thousands of miles!

WHERE DO EARTHQUAKES HAPPEN?

Earthquakes are most common in places where Earth’s plates bump against each other. More earthquakes happen in the area around the Pacific Ocean than anywhere else. The plate that makes up the bottom of the Pacific is constantly squeezed by the surrounding plates. The pressure causes earthquakes around the edges of the plate.

The edge of the Pacific plate runs along the western coast of North and South America. Japan, China, eastern Russia, and the countries of Southeast Asia lie on the other edge of the Pacific plate. All of these places have frequent earthquakes.

HOW POWERFUL ARE EARTHQUAKES?

Most earthquakes are small. The shaking is weak and lasts only a few seconds. You probably would not even notice a weak earthquake. Some earthquakes are very powerful. They cause a lot of shaking. The shaking can last for minutes. Powerful earthquakes destroy buildings, roads, and bridges.

Geologists (scientists who study the structure of Earth) can measure the power of earthquakes. They use seismographs (machines that record movements of Earth).

Geologists have scales that tell how powerful an earthquake is. The Richter scale uses a number to tell how powerful an earthquake is. An earthquake with a 3.5 on the Richter scale, for example, is strong enough for most people to notice. A 6.0 or higher earthquake is strong enough to cause damage to buildings.

HOW DO EARTHQUAKES CAUSE DAMAGE?

The movement of the ground during an earthquake makes buildings and bridges shake. If the buildings and bridges shake enough, they will fall down. Damaged buildings can catch on fire.

Earthquakes can also cause landslides. The shaking loosens rock and soil on the sides of mountains and hills. The soil and rock slides down. It can bury towns and neighborhoods.

Earthquakes can cause huge waves called tsunamis. Rock slipping along a fault under the ocean causes a tsunami. The sudden movement of the rock sends a shockwave through the water above it. It makes powerful waves of water on the ocean’s surface. The waves spread out across the ocean. When the waves reach shallow water near land they get bigger and taller. Tsunami waves can be 50 feet (15 meters) high! When a huge tsunami hits shore it causes terrible floods. The floods wash away cars and damage buildings. Many people can die when a tsunami hits land.

DO EARTHQUAKES HAPPEN OFTEN?

There are thousands of seismographs placed all over the world. The machines record about a million small earthquakes every year. There are about 20 medium-sized earthquakes each year. Very powerful earthquakes happen once every few years.

Earthquakes have killed several million people in the past 500 years. One of the worst earthquakes killed more than 240,000 people in China in 1976.

Candy

What do chocolate bars, jellybeans, caramels, lollipops, and licorice all have in common? Answer: They’re all types of candy.

WHAT IS CANDY?

Candy is one of the world’s most popular sweet-tasting foods. Sugar is the main ingredient in most candy. Other ingredients, such as honey, are sometimes used as sweeteners.

Many other ingredients are used in different candies. They include milk, eggs, flour, nuts, fruit, and flavorings such as vanilla and peppermint. The kinds of candy made are nearly endless!

WHAT ARE THE MAIN KINDS OF CANDY?

Candy comes in all shapes, sizes, colors, and flavors. Some candies are hard while others are soft and creamy or sticky and chewy. What’s the difference? It’s in how the candy is made.

Hard candies, such as lollipops and lemon drops, are made by boiling sugar with corn syrup and water. Butter or vegetable oil boiled with sugar produces butterscotch and brittles. Most brittles, including peanut brittle, are made with nuts.

Chewy candies, such as caramels and toffees, are made by boiling sugar, milk, and vegetable oil. Gumdrops are made by boiling sugar with gelatin or cornstarch.

Candies such as nougats and marshmallows are made by whipping air into sweet syrups. The air adds volume and makes the candy feel smooth in your mouth.

Chocolates are the most popular candies of all. Chocolate is made from the cocoa bean, a type of seed. Chocolate candies are sold mainly as solid bars, chocolate-covered bars, and other chocolate-covered treats.

THREE FUN CANDY FACTS

The simplest candy is cotton candy. It has one ingredient: sugar. The sugar is melted in a container with tiny holes and then spun very fast. The whirling container forces the sugar through the holes, making those thin threads that melt in your mouth.

The flavoring for black licorice comes from the root of the licorice plant. Licorice is one of the world’s oldest candies. The ancient Chinese, Egyptians, and Greeks used licorice as a medicine.

Do you know why a candy cane is curved at the top? Because shepherds often carried curved sticks, and the first visitors to the baby Jesus were shepherds. That’s why candy canes are especially made for Christmas, a day that celebrates the birth of Jesus.

WHEN DO WE EAT CANDY?

Candy is good just about anytime. But people eat more of it than usual at certain times of the year.

In the United States, where trick-or-treating is popular, the most candy is eaten around Halloween. The second-most popular time for candy is Easter. Many people receive Easter baskets filled with sweet treats. Next comes Valentine’s Day, which is for giving candy to loved ones and friends. Winter holidays such as Christmas, Hanukkah, and Kwanzaa are also special times to share candy.

Ice Cream

Ice cream is a frozen treat that comes in hundreds of flavors. What’s your favorite flavor? Is it vanilla? That’s the most popular flavor by far. Chocolate ranks second in popularity.

Ice cream is especially popular in the United States. In fact, Americans eat more ice cream than people in any other country.

MAKING ICE CREAM

Making ice cream is pretty simple. It’s usually made from milk, cream, sugar, and flavorings. Mix it all together as you freeze it and you get ice cream. As the mixture begins to freeze you can then add extra ingredients like fruit, nuts, or chocolate chips. If you freeze the mixture, you get regular ice cream. Soft ice cream is just regular ice cream that isn’t fully frozen yet.

Some people make ice cream at home in an ice-cream mixer, a special kind of home freezer. But nearly all ice cream produced today is made by machines in ice-cream factories.

CONES, BARS, SHAKES, AND MORE

How many ways are there to eat ice cream? There’s the ice-cream cone, which was made popular at the 1904 World’s Fair in St. Louis, Missouri. How about the ice-cream bar or the ice-cream sandwich? Do you like milkshakes? They’re made by blending milk with ice cream.

A fancier dessert is the ice-cream sundae. A classic sundae is ice cream served with chocolate syrup, whipped cream, nuts, and a cherry on top. A banana split is a sundae served with a slice of banana on each side. You can even eat deep-fried ice cream. Yes, it’s really fried! Or you can just eat ice cream all by itself.

OTHER FROZEN DESSERTS

There are many other popular frozen desserts that are similar to ice cream. Sherbet is made from fruit syrup that has milk or egg white added to it. Spumoni is an extra-rich ice cream with fruits and nuts. Ice milk, also called low-fat ice cream, is made with milk instead of cream. Soft-serve ice cream is served before it’s fully frozen.

You can even get ice cream made without milk or cream. Soy ice cream and rice ice cream are made without dairy products. They’re made using soybean milk or rice milk instead.

MANY FLAVORS

You’ve probably eaten vanilla and chocolate ice cream. Other favorite flavors include strawberry, cherry, peach, butter pecan, and chocolate mint. But have you ever eaten ice cream flavored with garlic or green tea? Some people do.

Ice cream comes in countless flavors. Imagine tasting burnt-caramel ice cream. How about coffee- or molasses-flavored ice cream? You can even buy ice cream flavored with rose petals!

Fish

What kind of animal can live in hot desert spring water or in the freezing water of the Antarctic? What animal can live in a shallow mud pond or the deepest part of the sea? Fish can. Antarctic icefish can live in water below 32° Fahrenheit (0° Celsius). Desert pupfish can live in water that is hotter than 100° Fahrenheit (40° Celsius).

Fish are animals that live and breathe in water. Some fish live in the fresh water of lakes and streams. Some fish live in the salt water of oceans. A few fish can live in both kinds of water.

All fishes are vertebrates (animals with backbones). Most fish have a covering of scales to protect their bodies.

KINDS OF FISH

There are about 25,000 species (kinds) of fishes. Fish come in all sizes. The huge whale shark can be 40 feet (12 meters) long. The tiny goby is only 0.4 inch (1 centimeter) long.

Most fish are called jawed fish. Hagfish and lampreys are jawless fish. They are more like eels. Eels are fish that look like snakes. Jawless fish do not have fins, scales, or jaws with teeth.

All other fish have jaws. There are bony jawed fish and cartilaginous jawed fish. Bony fish have skeletons made of bone. Cartilaginous fish have a softer material called cartilage instead of bone. Sharks, rays, and chimaeras are cartilaginous fish.

HOW FISH SWIM

Most fish use their side, back, and tail fins for swimming. Fins are movable, fanlike parts. A fish moves through the water by swinging its tail fins back and forth. A fish uses its other fins to steer and to stop. Sometimes the other fins also help it go fast through the water.

Most fishes have bodies shaped like a torpedo. Their bodies are pointed at the head and at the tail. This streamlined body helps fish speed through water. Sailfish can swim as fast as 70 miles per hour (110 kilometers per hour).

Some fish have unusual shapes. Rays have flat, disc-shaped bodies. Large fins like wings go out from a ray’s head. To swim, rays flap the fins.

Most fish also have swim bladders. They fill their swim bladders with air. Their air-filled swim bladders act like life jackets. They keep the fish from sinking to the bottom.

HOW FISH BREATHE

You have lungs for breathing. Most fish have gills for breathing. Gills have thin tubes that carry blood. As water goes into a fish’s mouth it passes over the gills. The gills take oxygen out of the water. All animals must have oxygen to live. Blood in the gills picks up the oxygen and takes it everywhere in the fish’s body. A waste gas called carbon dioxide also goes out of the fish’s body through the gills.

The lungfish can breathe air. Most lungfishes rise to the water’s surface to breathe. Some get oxygen from the water.

FISH SENSES

Fish have a great sense of smell. They use their sense of smell to find food. Most fish can see. Fish that live at the bottom of the sea in total darkness cannot see. Some do not have eyes.

Fish can also feel things in the water around them. They can feel things before they can see them. They can tell if a big, dangerous fish that might eat them is coming near.

Minnows can tell when another minnow is being attacked. The skin of the minnow in danger gives off a chemical. The chemical warns other minnows to escape. Skin chemicals also help fish swim in groups called schools. By sensing skin chemicals, the fish in a school can all turn, stop, or swim away at one time.

WHAT FISH EAT

Most fish eat meat. Some eat tiny plants. Sharks and other big fish eat smaller fish. Some sharks eat seals.

Some fish have large, sharp teeth. Sharks and other big fish grab their prey and bite it. Other fish suck prey into their mouths and use smaller teeth to grind them up.

Some fish do not have teeth. Their mouths sift tiny plants and animals from the water. In the deep ocean where sunlight never reaches, the bodies of some fishes have chemicals that make a glowing light to attract prey.

HOW FISH REPRODUCE

Female fish lay eggs. Most kinds of female fish lay their eggs right in the water. Males fertilize the eggs. Some fish lay their eggs in nests on the bottom of a lake or ocean and guard the nests.

Some male and female fish mate. Female guppies and sharks keep the eggs in their bodies until the baby fish hatch. Female pipefish and sea horses give the eggs to the male to take care of.

FISH AND PEOPLE

Fish are very important to people. People all over the world eat fish. People catch fish to sell. They catch fish for sport. You can keep fish as pets.

In some parts of the ocean, people are catching too many fish. In some lakes and rivers, pollution kills fish. Governments pass laws to limit fishing and clean up polluted water. These laws help keep fish from disappearing.

Sharks

When you think of sharks, you probably think of big jaws and teeth. That is what sharks are known for. Sharks are also known for their skill in hunting prey (animals they eat). But some sharks don’t hunt, and some have really small teeth. The largest sharks, the whale shark and the basking shark, use a kind of strainer, instead of teeth, to catch food. These sharks strain tiny plants and animals out of the water that enters their mouths as they swim.

SHARKS ARE FISH

A shark is a fish that lives in the sea. Sharks have lived on Earth for almost 400 million years. Today, there are about 375 species (kinds) of sharks. The smallest is the dwarf dogfish, less than 8 inches (20 centimeters) long. The huge whale shark can be more than 50 feet (15 meters) long.

Sharks, like all fish, are vertebrates (animals with a backbone). A shark’s skeleton, however, is not made of bone. It is made of a bendable material called cartilage.

Sharks, like other fish, are cold-blooded. They do not make their own body heat.

WHERE SHARKS LIVE

Sharks live in seas all over the world. Most sharks live in warmer waters. However, sharks have been spotted near the North and South poles.

Sharks live in salt water, but some can live for a while in fresh water. Bull sharks, for example, can swim up the Mississippi River.

Some kinds of sharks live in shallow water along coastlines. Other sharks live far out in the open ocean. A few species live deep down in the sea.

A SLEEK BODY

Sharks have long, streamlined bodies that taper in front and back. This shape lets sharks glide gracefully through the water. It also helps them put on great bursts of speed.

Most shark species have bodies that are from 3 feet (1 meter) to 6 feet (2 meters) long. The best-known sharks, however, are the biggest sharks. Hammerheads, tropical sharks with T-shaped heads, can be 12 feet (3.5 meters) long. Great white sharks are often more than 20 feet (6 meters) long.

A shark’s body may look smooth, but it is actually covered with tiny, rough scales. These scales feel like sandpaper to the touch.

HOW SHARKS SWIM

Sharks have several fins that help them swim. Their dorsal fins keep them steady in the water. Fins behind the head help them turn and move up and down. Fins near the tail help keep them level. The big tail fin, however, is what really makes a shark go fast.

If a shark stops swimming, it will fall to the sea bottom. Unlike other fish, a shark does not have a swim bladder. An air-filled swim bladder helps fish float.

BREATHING

Most sharks have to keep swimming in order to breathe. Like all fish, a shark breathes through its gills. Gills take oxygen out of the water. All animals need oxygen in order to live.

Unlike other fish, a shark does not have the muscles to pump water through its gills. Sharks have to move in order for water to enter the gill slits on the sides of their heads.

TEETH AND JAWS

Most sharks have powerful jaws and rows of sharp, triangular teeth. They use their teeth and jaws to crush their prey or tear out pieces of flesh.

Your teeth are anchored in your jaw. A shark’s teeth are set into its gums. Sharks often lose teeth while eating. However, there are always rows of new teeth growing behind the first set. As a shark loses teeth, new ones move forward to replace them.

SHARK SENSES

A shark’s sense of smell is so powerful that it can detect odors in the water hundreds of meters away. Sharks’ eyes detect very small movements and can see in dark waters.

Sharks, like other fish, have a special sense called the lateral line, which runs around the side of the body and into the head. It can sense the tiniest vibrations in the water caused by sounds or animal movements. Sharks can also sense weak electrical currents from nerves and muscles in living animals.

HOW SHARKS REPRODUCE

Females in some shark species lay eggs outside their bodies. Others keep the eggs in their bodies until they hatch. Still others give birth to live young much the way mammals do.

Sharks have between and 1 and 20 babies, or pups, at a time.

HUNTING AND EATING

Fish is the favorite food of most meat-eating sharks, along with shellfish. Great white sharks will sometimes eat larger prey, such as seals, dolphins, whales, and other marine mammals.

Sharks play an important role in keeping ecosystems in balance. Sharks often eat weak or diseased animals. Biologists fear that without sharks, the number of other animals in the sea would quickly grow out of control and eat all the food. It might take many years to restore the delicate balance that sharks help maintain.

SHARKS AND PEOPLE

Sharks have a reputation for attacking people, but these attacks are rare. One study showed that there are fewer than 100 shark attacks worldwide in a year. Most of the victims do not die. Researchers believe that sharks often attack humans by mistake, thinking that they are prey.

People are actually a bigger threat to sharks. Humans hunt sharks for sport, food, medicine, and leather (skin). Shark meat and shark-fin soup are popular in many places around the world. Some people hunt sharks just for their fins, throwing the rest of the shark back in the sea to die. Because of this, some sharks have become endangered. Scientists are trying to decide how best to protect sharks so they won’t disappear.

Air Force

Although armies and navies have been fighting for thousands of years, air forces are fairly recent. An air force needs airplanes, and the airplane was only invented in 1903. The airplane soon became an important weapon of war.

Planes equipped with machine guns shot one another out of the sky for the first time during World War I (1914-1918). Pilots sometimes tossed hand grenades (small bombs) from the cockpit onto enemy troops on the ground.

WHAT DOES AN AIR FORCE DO?

Today, most nations have an air force for their defense. An air force protects a country from attack by air. It uses radar and airplanes to detect enemy aircraft. Fighter planes and missiles then intercept and destroy enemy airplanes.

Air forces can also attack. Bomber planes drop bombs on enemy territory. Bombers try to knock out targets on the ground and prevent the movement of troops and supplies. Fighter planes conduct combat in the air with enemy aircraft. Missiles carry explosive weapons that attack targets in enemy territory.

The air force plans and carries out military operations along with the army and the navy. Another job of the air force is to transport troops and supplies.

WHEN DID AIR FORCES DEVELOP?

People began to think about the military possibilities of airplanes soon after the airplane was invented. After World War I, some military experts thought the next war would be decided by air power. Others disagreed.

Air power played a major role in World War II (1939-1945). Germany’s Luftwaffe (air force) tried and failed to defeat Britain’s Royal Air Force in the Battle of Britain in 1940. Airplanes that were based on aircraft carriers at sea carried out bombing raids on the enemy. Although bombing did not decide the outcome of World War II, it played an important role in the defeat of Germany and Japan.

In 1947, after the war ended, the United States government created an independent U.S. Air Force. Until then, the air force had been a branch of the U.S. Army. Today, the United States has the strongest air force in the world.

Army

What do knights wearing shining armor, archers carrying longbows, men marching in orderly lines, cannons, guns, and bombs have in common? They’re all developments that improved armies. Armies have been around for thousands of years.

WHAT’S AN ARMY?

An army is the portion of a country’s armed forces that fights on land. (The navy fights at sea, and the air force fights in the air.) An army includes soldiers, weapons, and other equipment. It also includes a support system set up to provide soldiers with transportation, supplies, medical care, and information about the enemy.

WHAT DOES AN ARMY DO?

Armies defend countries against invasion. They can also invade other countries or occupy other countries to keep the peace.

Armies do more than just fight wars. They also help out during natural disasters, such as hurricanes and floods. Sometimes they build roads, railways, and bridges. They can also help keep the peace inside their own countries during riots and other unrest.

SOLDIERS

In ancient times many soldiers were untrained volunteers who had to supply their own weapons and equipment. Modern armies pay, train, and equip their soldiers. Countries sometimes draft soldiers, especially during big wars or when they’re being invaded. Drafted soldiers don’t have a choice—they have to serve in the army.

Soldiers tend to be young, in their late teens or early twenties. They have to be healthy and able to run fast and carry heavy loads. Soldiers have generally been men throughout history. During the 20th century many countries began to allow women to be soldiers. Officers in armies command groups of soldiers.

WEAPONS AND EQUIPMENT

Soldiers need lots of equipment to fight and protect themselves. In the past that meant swords, armor, horses, or bows. Today it means guns, uniforms, vehicles, tanks, bombs, and even computers.

In modern armies, soldiers wear bulletproof clothing and use guns with laser aiming devices that tell them exactly where they’ll hit. They consult computers that show what the surrounding land is like and where enemy troops are. Huge planes carry troops and even tanks from place to place.

Tanks

Imagine you are a soldier. You have a scary job. You have been ordered to attack enemy soldiers hiding behind brick walls.

What do you need for this job? You want to smash through the walls, and you want to protect yourself from harm. Armies have machines for doing this. These machines are called tanks.

WHAT ARE TANKS?

Tanks are large, heavy war machines. They carry a large cannon on the top. This gun can turn all the way around and fire in any direction. Most tanks also have two machine guns. Some tanks can fire missiles.

Tanks are heavy because they have a thick covering of steel. This steel protects the tank’s crew from enemy gunfire. The steel is at least 6 inches (15 centimeters) thick. Bullets bounce off a tank. But a cannon shell or missile can pierce the tank’s covering.

Most tanks carry a crew of four soldiers. One soldier is the tank commander. A second drives the tank. A third loads the guns. A fourth fires the guns.

HOW ARE TANKS USED?

Battle tanks attack enemy defenses and fight other tanks. These tanks can crush almost anything that stands in their way. The largest and heaviest tanks are battle tanks.

Some tanks are lighter and faster than battle tanks. They also have smaller weapons. These tanks are used to scout around and find where enemy soldiers are located.

Britain used the first tanks in 1916 during World War I. Tanks protected soldiers from machine-gun fire, rolled over trenches, and smashed through barbed wire.

Germany used tanks to win many quick victories in 1939 and 1940 at the start of World War II. The German army overwhelmed armies that didn’t have tanks. Tanks have taken part in almost all wars since World War II.

HOW FAST CAN TANKS GO?

Even though they are heavy, tanks can travel quite fast. Some tanks move as fast as 60 miles per hour (97 kilometers per hour) on a road or level ground. On rough ground, a tank rumbles along at slower speeds. Lighter tanks can move faster than heavier tanks.

A tank moves on two tracks. A tank’s tracks are not the same as train tracks. Tank tracks are huge, flexible belts made of steel plates connected together. Tracks make it possible for a tank to travel across rough ground that might stop a car or truck.

Airplanes

Airplanes are a relatively recent invention. The first one flew just over 100 years ago. As little as 50 years ago, only small numbers of people had ridden in an airplane. Today, air travel is one of the most common means of transportation.

Hundreds of thousands of people fly on airplanes each year. You buy your ticket. You pack your suitcase. Then, off you go to the airport.

The airport is where planes take off and land. An agent takes your suitcase. You go to a gate (loading and unloading area) and get on your plane. There are rows and rows of seats. You sit down next to a window. You fasten your seat belt. You are ready to take off.

PARTS OF AN AIRPLANE

The place where you sit is called the cabin. The cabin is in a long tube called the body, or fuselage, of the airplane. The front of the fuselage is called the nose. The pilot and copilot sit in the cockpit right behind the nose. The pilot steers the plane in the cockpit. Your suitcase is stowed in the cargo hold under the cabin.

Two big wings stick out from the fuselage. In back of the wings are moveable parts called flaps and ailerons. These parts help control the plane. A big tail sticks up from the end of the fuselage. A rudder, located on the back of the tail, helps the plane turn left and right.

Sets of wheels sit underneath the airplane. The airplane rolls on the wheels before it takes off and after it lands. The wheels on big planes go up into the fuselage when the plane is in the air. They come down before the plane lands.

AIRPLANE ENGINES

There are different kinds of airplane engines. Propeller engines turn propellers on the nose or on the wings. Propellers pull an airplane through the air.

Jet engines suck air in. They heat the air and shoot it out of the back of the engine. Jet engines push the plane through the air. Turboprops are a combination, using the power of a jet engine to turn a propeller.

HOW PLANES TAKE OFF

Airplanes are heavier than air. They need to go fast in order to fly. Engines and wings make a plane fly.

An airplane builds up speed on a runway. Runways at airports are long concrete strips. Runways in some faraway places can be level places made of dirt or grass. Some planes can even take off on water. When the plane is going fast enough, the pilot takes it up into the air.

FLYING A PLANE

The pilot uses many controls in the cockpit to fly a plane. The pilot pulls a wheel or stick back to make the plane go up. Air rushing over and under the wings lifts the plane into the sky.

Dials on a control panel in the cockpit tell the pilot how high the plane is, how much fuel it has, and which direction it is heading. A radar screen tells the pilot if other planes are nearby. The pilot uses the rudder on the tail and the ailerons on the wings to make the plane turn.

HOW PLANES LAND

It’s time to land. The pilot pushes the wheel or stick forward to make the plane go down. The pilot lowers the wheels and landing gear. The plane touches down on the runway. The pilot uses brakes to slow and stop the plane.

THE WORK OF AIRPLANES

Planes do different kinds of work. Passenger planes carry people in the cabin. Cargo planes carry packages, boxes, and other things. Cargo planes do not have seats.

Military cargo planes can carry soldiers, tanks, and cannons. Some military planes are fighter jets. Some are bombers. Some military jets take off and land on aircraft carriers at sea. Certain military planes can take off straight up like a helicopter, then fly ahead like a plane.

Crop-duster planes spray farm fields with chemicals that kill bugs or fertilizer that helps crops grow. Firefighting planes drop water or chemicals on forest fires. Seaplanes have skis instead of wheels. They can land on lakes in faraway places to deliver passengers, supplies, and mail.

BIG AND SMALL PLANES

The smallest airplanes are called ultralights. They weigh about 100 pounds (about 46 kilograms) and carry only a pilot. The biggest planes are jumbo jets. They can carry several hundred people and several hundred tons of cargo. Jumbo jets fly long trips over oceans.

In between, there are planes of many sizes. There are two-seater and four-seater propeller planes. There are commuter planes that can carry about 20 passengers on short trips. Airlines also fly many jets that hold from 80 to over 400 passengers.

THE FIRST AIRPLANES

Long ago, people dreamed of flying like the birds. They tried to build machines that would fly. The first people to succeed were two American brothers, Orville and Wilbur Wright. They made a heavier-than-air machine of wood and cloth. It had an engine that turned a propeller. The brothers made their first flight near Kitty Hawk, North Carolina, on December 17, 1903.

The Wright brothers and other inventors experimented with different designs. They made better and better planes. The first warplanes flew during World War I (1914-1918). Then, pilots started taking passengers on trips. Jet engines in the 1950s made air travel faster and made passenger planes very popular. Now, millions of people travel everywhere on airplanes.

AIRPLANES OF TOMORROW

Today, there are planes that can fly as fast as the speed of sound. Inventors hope to make planes that can fly five times faster than sound. They want these planes to fly up to the edge of space. Then the planes will come back down and land. They call these planes hypersonic planes. Today, it would take you more than 12 hours to fly from Chicago, Illinois, to Tokyo, Japan. In a hypersonic plane, you could make that trip in two to three hours.

Engines and Motors

What do a toy car, a blender, a jet plane, a tape recorder, a refrigerator, a lawn mower, a fan, a helicopter, a printing press, an electric drill, and a speeding train all have in common? They contain an engine or motor.

HOW DO ENGINES WORK?

An engine is a machine that makes energy more usable. Engines usually turn heat energy into motion.

Think of a roaring campfire. The fire puts out lots of energy. The fire’s energy may keep you warm, but it won’t take you to soccer practice. An engine can take heat energy and turn it into motion.

The engine in a car, for instance, burns gasoline to make heat. The engine burns the gasoline in small, controlled explosions. These little explosions move parts of the engine up and down. The motion spins a shaft, which is connected to the car’s wheels. When the shaft spins, the wheels turn.

Engines often get hot when they run. They need to be cooled. Most are cooled by air blowing over them. Some use water or other means to take extra heat away.

WHAT POWERS AN ENGINE?

Engines need a source of energy to make them go. Car engines use gasoline, but gasoline is not the only source of energy for engines. Different types of engines use different energy sources. Steam engines use boiling water. Other engines use wood, coal, electricity, or other fuels. The engines turn the energy from these sources into movement.

Engines are sometimes called motors. Some people like to be more specific with the word motor. They only use the term motor to mean engines powered by electricity.

HOW DO ELECTRIC MOTORS WORK?

A motor turns electrical energy into motion. A motor is made from a magnet with a wire wrapped around it. Electricity moving through the wire spins the magnet around!

The spinning magnets are attached to the wheels on a toy car, or the blades of a fan, or whatever the motor is connected to.

The most common motors are called squirrel-cage motors. They look like the wheel a pet hamster might have in its cage for exercise.

TYPES OF ELECTRIC MOTORS

Electric motors use two different types of electricity to run. The kind that flows into your house through the plug on the wall is most likely alternating current, or AC. Most of the motors you use in your house are probably AC motors.

The other type of electricity is called direct current, or DC. DC motors are found many places as well. If you have a toy that runs on batteries, it probably has a DC motor inside.

Some motors are specially designed to run on either type of electricity.

Automobiles

People in the 1800s didn’t know what to think about a new invention called the automobile. No one was sure it would catch on. In those days, people often traveled in carriages pulled by horses. So when the first automobiles appeared, people nicknamed them “horseless carriages.”

The first automobiles looked a lot like horse carriages. That was the style people knew. But the automobile soon took on a look that was all its own. The modern automobile has a hood and fenders. It has a roof, sides, and four wheels. It has seats where the driver and passengers sit. Modern automobiles are commonly called cars or autos.

Few machines are as important as cars. You can ride to school in one. Adults can drive one to work. You can drive in a car to shopping malls. You can take long vacations traveling in an automobile.

TYPES OF CARS

The typical passenger car can carry up to six people. Larger vehicles called minivans are like big cars. They can usually carry up to eight people. Pickups or trucks are built to carry cargo.

Sport-utility vehicles (SUVs) are made for driving in all types of conditions, including mud or snow. Sports cars are built for power and good road handling. Many sports cars have room for just two passengers.

Racing cars are specially designed to compete on tracks and courses. Most racing cars are built to be lightweight and very fast. Because they are made for racing, they usually are not suited for driving on public streets.

WHAT MAKES CARS GO?

A car gets power from its engine. Most auto engines burn gasoline. Gasoline goes through fuel lines from a gas tank to the engine.

When it burns fuel, the engine makes exhaust gases. These gases go out through pipes called the exhaust system.

Moving parts hooked up to the engine are called the drivetrain. The drivetrain carries mechanical energy from the engine to the wheels. The turning wheels make an automobile go.

Springs and shock absorbers give passengers a smoother ride on bumpy roads. Electrical parts make the headlights, turn signals, horn, radio, and windshield wipers work. The electrical parts also help start the car. Brake parts rub against the wheels to slow the car down. Seat belts and air bags help protect you in an accident.

HOW DO YOU DRIVE A CAR?

People don’t just jump into cars and start driving. First, they must get their learner’s permit. Local auto bureaus can tell you how. Driver-education classes teach people how to drive a car. Students learn how a car works and the rules of safe driving.

To start a car, you sit in the driver’s seat. Turning a key in the ignition starts the engine. Moving the car’s gearshift connects the engine to the drivetrain. Pressing the gas pedal on the floor sends fuel to the engine. The harder you press, the faster the car goes.

To make the car turn left or right, you turn the steering wheel in the direction you want to go. To make the car move forward or backward, you use the gearshift.

What about stopping? Press your foot down on the brake pedal. The brakes will press against the wheels, making them slow down and then stop turning.

WHEN WERE THE FIRST CARS MADE?

The first cars were built in the 1700s. They were powered by steam engines. In England, steam-powered cars weren’t allowed on the roads. They were run like trains on private railroad tracks!

Auto racing became popular in the late 1800s and early 1900s. Some early racing cars had steam engines. These included the American-made Stanley Steamer. In 1906, a Stanley Steamer hit a speed of more than 121 miles per hour (195 kilometers per hour), setting a new land speed record.

Other cars made at the time ran on electricity from batteries. People liked them because they were quiet and less likely to scare horses and people. Still other cars had gasoline engines. The first gasoline-powered cars were loud, slow, and unreliable. But over time, the cars were improved, and more people wanted to drive them.

HENRY FORD INVENTS THE ASSEMBLY LINE

In the United States, a businessman named Henry Ford started the Ford Motor Company in 1903. His company made two famous kinds of cars: the Model A and the Model T.

Ford invented the factory assembly line for making cars. Workers in one place along the assembly line worked on just one part of the car. Other workers, in another area of the assembly line, worked on another part of the car.

Automobiles made this way were not very expensive. Ordinary people could afford them. The Model T became one of the biggest-selling automobiles of all time. Henry Ford sold more than 15 million Model T cars before his company stopped making them in 1927.

MODERN CARS

Modern cars are much better than earlier models. They are easier to drive and have advanced safety features such as air bags. Engines are more efficient and powerful. Cars are quieter and more comfortable inside.

Today, cars are more popular than ever. They are the main form of transportation for many people in the United States and Canada. Many people own more than one car.

WHAT ABOUT AIR POLLUTION?

The exhaust gases that come from burning gasoline can pollute the air. These gases contain chemicals that cause a smoky pollution called smog. The worst smog forms in cities. Exhaust gases also contain a gas called carbon dioxide. Scientists think carbon dioxide pollution is making Earth’s climate warmer.

Scientists and engineers are working to reduce pollution from cars. They have made cars that burn less gasoline. They have designed exhaust systems that give off less pollution. They have also developed efficient hybrid cars.

HYBRID CARS

Many people believe hybrid cars could be a big help in reducing pollution. Hybrid cars are automobiles that run partly on gasoline and partly on some other fuel. Most hybrid cars use electricity from batteries. Scientists are also experimenting with hybrids that run on energy from sunlight and other sources.

Gasoline

Gasoline makes cars run. This liquid is very important to us. A car’s engine burns gasoline mixed with air. The energy released by burning gasoline turns the car’s wheels and makes the car go.

When the car starts to run out of gas, it’s time to fill up the car’s gas tank at a gas station. When you’re at a gas station, you’re probably standing on top of a huge underground storage tank. The pump brings the gasoline up from the storage tank, and a hose feeds it into the car’s gas tank.

Our world uses huge amounts of gasoline. The United States alone uses about 310 billion gallons (1.2 trillion liters) every year.

WHAT IS GASOLINE?

Gasoline is one of many substances found in oil, a natural liquid that forms deep underground. When this crude oil is pumped out of the ground, it’s a mixture of substances called hydrocarbons. They’re called hydrocarbons because they are made up of chains of the elements hydrogen and carbon. Different hydrocarbons have chains of different lengths.

Gasoline is a lightweight liquid at room temperature, but it becomes a vapor (gas) when warmed up. When gasoline vapor is mixed with oxygen from the air, a spark causes the mixture to burn quickly and give off a lot of heat. That’s what makes gasoline a good engine fuel. A car’s engine turns this heat into energy that turns the wheels.

HOW IS GASOLINE MADE?

Gasoline is separated from crude oil at factories called oil refineries. There are several ways to get the gasoline out. The oldest and simplest way is to boil the crude oil. Gasoline boils at a lower temperature than other parts of crude oil. Gasoline can be separated because it becomes a gas while the rest of the oil remains liquid.

The most common modern method for making gasoline is “cracking.” Longer, heavier hydrocarbon chains can be cracked into the smaller chains that make up gasoline. Gasoline produced by cracking burns more completely and evenly than gasoline produced in other ways. It makes an engine perform better and last longer.

GASOLINE AND AIR POLLUTION

Burning gasoline creates problems. It puts out gases that cause air pollution. These gases also cause global warming. Engineers and scientists are searching for solutions to these problems. Someday you may drive a car that is not powered by gasoline.

Motorcycles

What has two wheels, goes fast, and makes a loud noise? It’s a motorcycle, of course. Motorcycles look like bicycles, only they’re bigger and much heavier. Most motorcycles have engines that run on gasoline, just like cars.

MOTORCYCLE BASICS

On a motorcycle, the engine is bolted to a steel or aluminum frame. Two wheels are attached to the frame. Power from the engine turns the rear wheel. A fuel tank sits above the engine, just behind the front wheel. The seat is behind the fuel tank, toward the rear wheel.

Many motorcycles have a small trunk underneath or behind the seat. Typically, two people can ride a motorcycle at one time, the driver and one passenger. Some motorcycles have a sidecar (a compartment with its own wheel) attached for a passenger to ride in.

Motorcycles are ranked by engine size. The bigger the engine, the bigger and faster the motorcycle. Engines are measured in cubic centimeters, or cc’s. They can range from 50 cc, the engine size used in a small, lightweight motorcycle, to 1,500 cc or more. A 1,200 cc motorcycle is a big, powerful motorcycle—that’s the size police officers usually ride.

For comfortable riding, motorcycles have shock absorbers mounted to the front and rear wheels. This is called the suspension system. Shock absorbers cushion the rider from bumps and jolts on the road.

TYPES OF MOTORCYCLES

People use motorcycles in many different ways, so motorcycles take different forms. They include street motorcycles, off-road motorcycles, and road-racing motorcycles.

WHAT ARE STREET MOTORCYCLES?

Most motorcycles are street motorcycles. They are made to be driven on paved public roads. Street motorcycles come in all different sizes, but they have much in common. They all have lights, a horn, mirrors, and a muffler—just like cars. Many street motorcycles have a windshield, called a fairing. A fairing helps protect a rider from the wind. It also makes a motorcycle more streamlined, so it can go faster.

Street motorcycles can usually reach top speed faster than cars, and they can stop faster and make sharper turns. They also get better gas mileage than cars, and they take up less parking space, too! In the United States and Canada, you need a special driver’s license to operate a street motorcycle on public roads.

WHAT ARE OFF-ROAD MOTORCYCLES?

Compared to street motorcycles, off-road motorcycles have lightweight frames and sit higher above the ground. Motorcycles made specially for off-road use are often called dirt bikes. Trail bikes are motorcycles made for both on- and off-road use.

Off-road motorcycles have extra-wide tires with special “knobby” tread for good traction on dirt and trails. They have flat, wide handlebars to give the rider good control over bumpy ground.

In motocross, a type of off-road motorcycle competition, cyclists race each other around a dirt track. Motocross tracks often have jumps, tight turns, and a section of big bumps called whoops.

WHAT ARE ROAD-RACING MOTORCYCLES?

Most road-racing motorcycles are built to be raced on special tracks. They are light, quick-turning, and very powerful. They have stiff suspension systems for better handling through high-speed turns.

Road-racing motorcycles are among the world’s fastest motorcycles. Motorcycles built for drag racing (sprinting down a straight-line course) are the fastest of all. Some can reach 242 miles per hour (390 kilometers per hour) from a standing start in the space of a few city blocks!

HOW DO YOU RIDE A MOTORCYCLE?

You start most modern motorcycles by pressing an ignition switch. You start most older motorcycles by forcefully pushing down on a lever with your foot. This is called a kickstart. Motorcycles made for motocross racing also use a kickstart instead of an ignition switch, because it saves weight.

You’ll find some of a motorcycle’s controls on its handlebars. You twist a grip on the right handlebar to give the engine gas. That makes the motorcycle go faster. You squeeze a lever on the right handlebar to work the front brakes.

Other controls are located by the rider’s feet. A foot pedal by the rider’s right foot works the rear brakes. A pedal by the left foot lets a rider shift gears to change the motorcycle’s speed.

Most motorcycles have five gears. First gear is for starting out from a stop. You shift through the gears to go faster. In fifth gear a rider can hit top speed.

MOTORCYCLE SAFETY

It’s important to remember that motorcycles take special skill to ride. Braking and turning require special care. It can be very difficult to stop or turn a motorcycle on slick or wet surfaces.

Riding a motorcycle is more risky than driving a car because the rider is out in the open. If you have an accident on a motorcycle, you can be seriously hurt. That’s why in most U.S. states and Canadian provinces, motorcycle riders must wear helmets. It’s the law.

MOTORCYCLES THROUGH THE YEARS

The German inventor Gottlieb Daimler built the first gasoline-powered motorcycle in 1885. He bolted a small engine to a wooden frame. It worked so well that he started making fancier motorcycles.

In 1903, John Harley and his neighbor Arthur Davidson made the first American motorcycle. Harley-Davidsons are still made today. They are famous for the deep, rumbling sound their engines make.

In the 1960s and 1970s, Japanese companies such as Honda and Suzuki started building high-performance motorcycles. Today, Japanese companies make some of the world’s best-selling motorcycles.

Bicycles

Riding a bicycle is a great way to get around. Bicycles are quiet, fun to ride, and you don’t need gas or electricity to make them go. You just use the power of your legs!

Bicycles have two wheels. One wheel is in front of the other. You swing your leg over the bike, sit down, and start pedaling.

PARTS OF A BICYCLE

The heart of every bicycle is its frame. Most bicycles have frames made of thin metal tubes. The best frames are light and strong. A seat, called a saddle, is in the middle of the frame. You can make the seat higher or lower.

Bicycle wheels usually have wire spokes. Spokes help the wheel keep its round shape. Inflatable tires fit on the wheels. The wheels have brakes for stopping.

A bicycle has handlebars. You use the handlebars to steer and help you balance on two wheels. Most bikes have brake levers on the handlebars. You squeeze the levers to make the brakes work.

Pedals and a chain make a bike go. You put your feet on the pedals and push. The pedals go around and around. The turning pedals move a chain. The chain goes to the back wheel. The chain goes around a part called a cog. The moving chain makes the cog on the back wheel turn.

Most bicycles have a gearshift attached to the frame or the handlebars. Bikes usually have from 5 to 27 gears. Bicycle gears have a part called a derailleur. The derailleur shifts the chain to lower or higher gears. You use a lever to shift gears.

You use low gears for going up a hill. You use high gears for going faster, usually on flat roads or downhill.

DIFFERENT KINDS OF BICYCLES

There are six basic kinds of bicycles: touring, mountain, hybrid, utility, racing, and specialty. Bicycles made for kids are smaller than those for adults. Training wheels may be added to help young riders learn basic balancing skills.

WHAT IS A TOURING BICYCLE?

Touring bicycles are for riding on smooth roads. Touring bicycles are made so you can ride them on long trips. You can carry water bottles, saddlebags to hold food and gear, and other equipment on a touring bike.

Touring bikes have lightweight frames and thin tires. They usually have handlebars that curve downward.

WHAT IS A MOUNTAIN BIKE?

Mountain bikes are for riding off-road on dirt trails. The frame of a mountain bicycle is usually smaller and stronger than a touring bicycle frame.

Most mountain bikes have flat handlebars. They have wide, knobby tires for going over rocks. They have a large selection of gears. Some mountain bikes have shock absorbers. Springs attached to the front or rear wheels make it easier to go over big bumps.

WHAT IS A HYBRID?

Hybrids are a cross between mountain bicycles and touring bicycles. You can ride a hybrid bike on smooth roads or on mountain trails. Many people ride hybrids in the city.

WHAT IS A UTILITY BICYCLE?

Utility bicycles are made to be reliable and inexpensive. They are not as fancy as other kinds of bicycles. They are heavier than other bikes and usually have wide, padded seats. They have flat handlebars and sturdy, wide tires.

WHAT IS A RACING BICYCLE?

Racing bicycles are the lightest bicycles. They have narrow saddles and very light, narrow wheels. Some racing bikes are made for road racing. Some are made for racing on special tracks.

Track-racing bicycles do not have brakes, derailleurs, or other parts that add weight. A track-racing bike can weigh as little as 13 pounds (6 kilograms).

WHAT ARE SPECIALTY BIKES?

Specialty bikes are made for special uses. Recumbent bicycles let you sit down as if you were in a chair. Your legs and feet stick straight out to reach the pedals in front. Tandems are bicycles made to carry two or more riders.

Bicycle-motocross (BMX) bicycles are modeled after dirt bike motorcycles. BMXs are popular among young people. Freestyle stunt bicycles have very strong frames and handlebars. Stunt bikes can spin completely around. Collapsible bicycles fold up into a compact shape so that you can easily carry them.

BICYCLE SAFETY

A bicycle helmet protects your head if you fall. Padded gloves can help keep your hands from getting scraped in a fall.

Other equipment also can help you ride a bicycle safely. Make sure your bike has front, side, and rear reflectors. You can also put a light on your handlebars. You can put a red flashing taillight on your bicycle seat or frame.

A rearview mirror can help you watch for cars coming up behind. You can use a bell or horn to warn people that you are coming.

WHO INVENTED THE BICYCLE?

No one person invented the bicycle. Some people think the bicycle dates back to drawings made by the Italian artist and inventor Leonardo da Vinci. He lived in the late 1400s and early 1500s.

In 1839, a Scottish blacksmith named Kirkpatrick Macmillan added pedals to a two-wheeled “hobby horse.” His invention was the first true bicycle. It had wooden wheels.

Inventors tried to make better bicycles. Bicycles in the 1870s had huge front wheels and tiny back wheels. The safety bicycle was invented in the late 1800s. Both wheels were the same size, so it was easy to ride. Bicycling then became very popular.

Trains

Have you ever stopped at a railroad crossing when a freight train rumbled by? Did you try to count the cars? Have you ever seen a high-speed passenger train whiz past? Trains are very important to transportation. Trains carry freight and people in places all over the world.

A train is made up of railroad cars hooked together and pulled by a locomotive. Locomotives are sometimes called engines. All trains run on tracks. Freight trains haul goods. Passenger trains carry people.

WHAT MOVES A TRAIN?

Locomotives push or pull railroad cars. They have powerful motors. The motors turn locomotive wheels that run on railroad tracks. Sometimes you will see three or four locomotives hooked together to pull a long freight train up a steep mountain.

Some locomotives get their power from electricity. The electricity comes from wires above the track or from a special third rail next to the track. Other locomotives get their power from diesel fuel, which is similar to the gasoline that most cars use. The kind of locomotive engines most used today are diesel-electrics. Engines that burn diesel fuel drive generators that make electricity. Powerful electric motors turn the wheels of a diesel-electric locomotive.

KINDS OF FREIGHT CARS

A freight train can have as many as 200 cars hooked together. There are special railroad cars for different kinds of freight.

The boxcar has four sides, a floor, and a roof. It looks like a box on wheels. Boxcars carry freight that has to be kept clean and dry, such as radios, television sets, and boxes of cereal.

Refrigerator cars work like your home refrigerator. They are boxcars that are cool inside. Refrigerator cars carry meat, fruit, frozen dinners, and other food that must be kept cold.

The hopper car is open on the top. Hopper cars carry coal, sand, gravel, and ore (rocks that contain metals). Hopper cars are easy to unload because they have doors on the bottom. The doors open and the coal, sand, or gravel pours out.

A flatcar has no top or sides. It has a floor on wheels. Flat cars carry lumber, steel beams, huge pieces of machinery, and other big items. Lifting machines called cranes load cargo onto flat cars. Special flatcars carry cars, boats, and trucks.

A tank car carries liquids or gases in a big, round tank that is lying on its side. Tank cars can carry milk, gasoline, or oil. Some tank cars carry dangerous chemicals.

KINDS OF PASSENGER CARS

Passenger cars have seats in rows along each side. Passengers can place small bags in a rack above the seat. Some passenger cars are made for long trips. They have seats that can be made into beds at night. Trains that carry passengers over long distances have special baggage cars to carry suitcases. They have dining cars where people can sit down and eat.

HOW DO TRAINS STAY ON THE TRACKS?

The track has two long rails made of steel. Pieces of wood or concrete called ties hold the rails in place and keep them from moving. Spikes hold the ties to the rails.

Locomotives, freight cars, and passenger cars have wheels that hold the train on the track. The wheels have a flange, a special shape that fits over the rails and keeps the train from slipping off the rails.

Railroad tracks are laid on a roadbed made of tightly packed dirt, gravel, or other material. When tracks have to go over rivers, the railroad company builds bridges. Sometimes railroad companies dig tunnels through mountains.

WHAT WERE EARLY TRAINS LIKE?

The first trains were wagons hooked together and pulled by horses, oxen, or other animals. The wagon wheels rolled over two strips made of wooden planks. Trains with wooden tracks were used as early as the 1500s to haul coal and stone. In the 1760s, iron rails replaced wooden ones.

Inventors made the first locomotives in the early 1800s. Early locomotive engines burned coal to heat water and make steam. The steam drove big pistons that turned the wheels. Inventors made bigger and better steam-engine locomotives. Steam engines drove most locomotives until the 1940s.

The first passenger cars were stagecoaches set on four railroad wheels. Then came larger cars with six wheels. In 1830, the Baltimore & Ohio became the first railroad in the United States to offer passenger service. The train was pulled by horses.

Passenger trains got better and better. In the late 1800s, a U.S. company called the Pullman Palace Car Company began making a comfortable sleeping car. Other companies made luxurious parlor cars for passengers to sit in. Train travel became very popular.

HOW HAS TRAIN TRAVEL CHANGED?

Many people traveled by train until the 1950s. Jet planes then began to replace trains as the most popular form of passenger travel. Today, most passenger trains in the United States and Canada are commuter trains. Passengers ride commuter trains twice a day between homes in the suburbs and jobs in the city. Trains continue to carry passengers between cities in Europe and in other parts of the world.

Some countries have high-speed trains. The first high-speed trains were in France and Japan. These trains can go about 260 kilometers per hour (160 miles per hour).

Engineers are working on a train that floats above its track. This type of train is called a maglev. Powerful magnets push the train a short distance above the rails as it moves along. Engineers are designing maglev trains that can travel much faster than trains on rails can.

Coal

Let’s imagine for a moment that there was no coal. Hey, who turned out the lights? And why isn’t the refrigerator working, or the TV? Much of the electricity we use comes from coal.

Coal is a black rock. It produces energy when it burns. The Chinese were mining and using coal for fuel over 3,000 years ago. It once powered the world’s industry. It helped make the United States a wealthy nation. Coal-burning trains carried people and products across the country. Today, coal-burning power plants produce electricity for many homes and businesses.

WHAT IS COAL?

Coal is mostly made up of the element carbon. When carbon burns, it releases a large amount of energy as heat. That’s what makes coal such a useful fuel.

Coal is a fossil fuel. That means it comes from the remains of ancient life buried deep in Earth’s crust. The coal we use today started out as plants that grew in swamps millions of years ago. When the plants died, they settled to the swamp bottom. Over time, layers of mud and rock formed. They compressed and hardened the plant material. Heat and pressure caused chemical changes. Gradually, the once-living matter became coal.

COAL MINING

Coal deposits are found in many parts of the world. Taking these deposits from the ground is called coal mining.

Some coal deposits lie close to Earth’s surface. They can be mined by scraping away the dirt and rock. This is called surface mining, or strip mining.

Other deposits lie deep underground. Miners must drill and blast deep holes in order to reach them. They bring machinery down to dig out the coal. This is called underground mining, or deep mining. Underground mines can be more than 1,000 feet (300 meters) deep. Their tunnels can be several miles long.

Deep mining is a dangerous job. Cave-ins, fires, and explosions are some of the dangers. Coal mining can also release poisonous gases. In the 1800s, miners would bring small birds into the mines as a safety alarm. If a bird died, it showed that there was poisonous gas in the mine. Today, miners use machines to test the air.

Surface mining is cheaper, easier, and safer than deep mining. But it scars the land. It can also create pollution and cause the soil to wash away.

HOW DO WE USE COAL?

A century ago, coal powered the steam engines that ran most machinery. Once, most American homes and office buildings were heated by coal-burning furnaces. Most of these jobs are now done by oil or natural gas.

Five-sixths of the coal mined today in the United States is used in electric power plants. Coal is also used in making iron and steel and in the cement- and paper-making industries.

PROBLEMS WITH COAL

Like other fossil fuels such as oil, coal is a nonrenewable resource. This means that once it’s used up, it’s gone. But the United States has a lot of coal. It would take hundreds of years to use it all.

Burning coal causes air pollution. Chemicals in coal can produce “acid rain.” Acid rain kills plants and pollutes rivers. However, machines called scrubbers can keep most of this pollution from getting into the atmosphere.

Burning coal also releases gases that cause global warming. These gases trap heat from the Sun. The trapped heat warms up the planet. Global warming could cause icecaps to melt and change Earth’s climate. Burning all of the coal available to us would be bad for the environment.

Oil

What would our world be like without oil? We wouldn’t have gasoline-powered cars. We wouldn’t have airplane fuel or oil to heat our homes. Many paints, fertilizers, and kinds of cloth are made partly from oil. So are many plastics, chemicals, building materials, and even medicines.

It’s hard to imagine life without oil. Yet the world’s supply of this valuable resource is running out.

WHAT IS OIL?

Oil is the purified form of a black or brown liquid called crude oil. Crude oil is a mixture of substances called hydrocarbons. They’re called hydrocarbons because they are made up of the elements hydrogen and carbon. Hydrocarbons give off a lot of energy when they burn. That’s why they make good fuels. They also can be combined with other elements in many ways to make different products.

Crude oil forms under Earth’s surface. It forms from the remains of sea animals and plants. (This is why oil is called a fossil fuel—it comes from fossils.) When these living things die, they sink to the sea bottom. Over millions of years, they form a thick layer. The layer can get buried under sand and rock. Pressure and high temperatures inside the planet change it into oil and natural gas.

Most crude oil is trapped far underground. But it seeps through to the surface here and there, forming pools of black liquid. People have known about these pools for thousands of years. In the 1850s, chemists began to discover different ways crude oil could be used. These discoveries set off a massive search for oil. This search is still going on today.

EXPLORING FOR OIL

Scientists and engineers explore for crude oil beneath the ground. They look for particular kinds of rock and land features on Earth’s surface. They explore underground with sound waves.

But there is really only one way to prove that crude oil is present. You have to drill an oil well. Only about one-third of wells dug for exploration strike oil. The rest turn out to be “dry.” More oil sources have been found by lucky guesses than by science.

Oil wells don’t keep pumping until the crude oil is all gone. Less and less oil comes up as a well begins to go dry. A well is only used until it costs more money to get the oil out than the oil can be sold for. At that point the well is capped.

REFINING CRUDE OIL

To be useful, crude oil must be cleaned and purified. Then it must be separated into different substances. This process is called refining. Crude oil is refined at huge factories called oil refineries. Gasoline, fuel oil, asphalt, waxes, and other hydrocarbons can be separated from crude oil at various temperatures. Then, they can be processed for different uses.

A NONRENEWABLE RESOURCE

Oil is a nonrenewable resource. The supply is limited. It takes millions of years for oil to form. Once oil is used up, it’s gone.

Nobody worried about this problem 100 years ago. But the world is using more oil each year. Today, oil supplies about two-fifths of the energy used in the United States. Americans use about 700,000,000 gallons of oil every day (about 2,650,000,000 liters). About two-thirds of it is used as fuel for cars, airplanes, trains, and other vehicles.

New sources of crude oil will probably be discovered. So will new ways of draining the last drops of oil from known sources. Even so, most experts agree that the world’s oil reserves will be largely gone by the year 2050.

Magnets

Hold a refrigerator magnet close to your refrigerator door. Let go of it. If you are close enough to the refrigerator, the magnet will jump across empty space and stick to the refrigerator. This action might seem kind of mysterious. But it makes sense when you know what magnetism is.

Magnetism is an invisible force. Magnetic force can attract (pull toward) or repel (push away). Magnetism comes from magnets. Magnets make things move without touching them. Some magnets are weak. Other magnets are much stronger.

Some rocks, such as lodestone, are natural magnets. Iron and some other metals can be made into magnets. Cloth, rubber, plastic, and many other things cannot be made into magnets.

SHAPES OF MAGNETS

Some magnets are shaped like the letter U. Some magnets are shaped like bars. Magnets can also be thin disks, squares, or rectangles. Other magnets are round or have irregular shapes.

Magnets can be big or small. Earth is a giant magnet. The Sun, stars, and some other planets are also magnets. Atoms can be magnets. Atoms are tiny bits of matter much too small to see.

NORTH AND SOUTH POLES

The important thing to remember about a magnet is that it has two ends called poles. One end is called the north pole, and the other end is the south pole. The south pole of one magnet will attract and stick to the north pole of another magnet. The south pole of a magnet will repel, or push away, the south pole of another magnet. North poles will also repel each other.

MAGNETIC FIELDS

Hold the north pole of one magnet close to the south pole of another magnet. Don’t let them touch. You can feel the magnets tugging toward each other. Now try to bring the north poles of both magnets together. You can feel the magnets pushing away from each other.

Magnets are surrounded by magnetic fields. You feel magnetic pull or push inside the magnetic field. Move the magnets farther apart. The pull feels weaker. The farther you go from a magnet, the weaker its magnetic force becomes. Magnetic fields are strong close to a magnet and weak far away. If you hold the magnets far enough from each other, you will not feel them pull at all.

MAKING A MAGNET

Long ago, people in Greece, Rome, and China found that lodestone could pull iron toward it. Lodestone is made of the mineral magnetite. When they rubbed a piece of iron with lodestone, the iron became a magnet, too. People in ancient times did not know it, but rubbing made tiny magnets inside the iron all line up in the same direction. All the north poles were pointed the same way. So were the south poles.

In the 1200s, sailors learned how to make a compass that could help them find their way at sea. They made a needle from a thin piece of lodestone or iron. They hung the needle from a string. The needle always pointed north. Because Earth is a big magnet, the south pole of the compass needle always points toward the magnetic North Pole of Earth. Remember, the south pole of one magnet always pulls toward the north pole of another magnet. This works whether the magnet is as small as a needle or as big as a planet.

In the 1800s, people learned that magnetism is related to electricity. They learned how to make magnets by winding electric wire around a piece of iron. These magnets are called electromagnets.

PERMANENT AND TEMPORARY MAGNETS

Permanent magnets always have magnetic force. Lodestone is a natural permanent magnet. Other permanent magnets can be made from mixtures of metals such as iron and nickel.

Temporary magnets are made from materials that must be inside a magnetic field to have magnetism. Electromagnets are temporary magnets because they must have electricity to work. Electromagnets cannot pick up heavy loads if the electricity is turned off.

Some materials can never be turned into magnets. These materials include cotton, glass, paper, plastic, rubber, and wood.

HOW WE USE MAGNETS

You can use a magnet for holding notes and pictures on your refrigerator door. But people use magnets for many other things. Radios and TVs need magnets in order to work.

Electric motors need electromagnets. Electric motors drive many appliances in your home. There are electric motors in washing machines, vacuum cleaners, fans, and many other things. Electric motors also drive big machines in factories. They drive engines in some trains and ships. Big magnets in electric generators help make the electricity you use in your home.

Huge electromagnets can pick up heavy loads. Some electromagnets can even lift cars. Electromagnets also make a powerful type of microscope, called an electron microscope, work.

Magnetic materials can store information. Videotapes and computer hard drives use tiny magnets to record information.

Doctors use machines with powerful magnets to make pictures of the inside of the body. These pictures are made by a method called magnetic resonance imagining (MRI).

Scientists and engineers are working on trains that float above the track. Magnets in the train and track push away from each other to lift the train a short distance above the track. These floating trains are called magnetic levitation, or maglev, trains.

Air

Take a really deep breath. Feel how your chest gets bigger and bigger. Your chest gets bigger because your lungs are filling up with air. You cannot see air, but air is all around you. You can feel it when the wind blows.

Earth’s atmosphere is made of air. An atmosphere is made up of the gases that surround a planet.

WHAT IS AIR?

Air is a mixture of several different gases. The main gases in air are nitrogen, oxygen, and argon. Air also contains smaller amounts of hydrogen, carbon dioxide, water vapor, helium, and other gases. Oxygen is the most important gas for animals. Animals must breathe oxygen in order to live.

Carbon dioxide is the most important gas for plants. Plants use carbon dioxide and sunlight to make food. Plants give off oxygen. Animals turn the oxygen back into carbon dioxide when they breathe.

TAKING AIR WITH YOU

You can go to places where there is no air. There is no air underwater, but you can dive underwater. You can stay underwater a short time just by holding your breath. Air tanks let you stay underwater for a long time. Scuba divers wear tanks on their backs. The tanks are filled with gases that make up air. The divers breathe the gases through hoses.

There is less and less air the higher up you go. People gasp for breath at the tops of tall mountains. Airplanes must carry air. Once the airplane gets up high, air is pumped into the cabin where passengers sit. Astronauts have to take all the air they need with them—there’s no air in space!

Albert Einstein

Dents in space, light in bundles, and matter that turns into energy sound like science-fiction fantasies. However, Albert Einstein said they were real. Other scientists proved through observations that Einstein’s theories were right. Einstein revolutionized the science of physics and helped bring in the atomic age.

WHERE DID EINSTEIN GROW UP?

Albert Einstein was born in Ulm, Germany, on March 14, 1879. He grew up in Germany, Italy, and Switzerland. Einstein taught himself geometry when he was 12 years old. School bored him because it required endless memorizing and reciting. He often skipped classes to study on his own or to play his violin. Yet he graduated from college in 1900 and earned a Ph.D. degree in 1905. From 1902 to 1907, Einstein worked as a clerk in the patent office in Zürich, Switzerland. His job left him plenty of time to think.

WHAT DID EINSTEIN THINK ABOUT?

Einstein thought about the rules that govern the way the world works. For example, he explained why small particles in liquids wiggle around, a movement called Brownian motion. He said that the particles were being bumped into by tiny bits of matter called atoms that are too small to see.

He also thought about light and electricity. Einstein knew that light shining on metal sometimes causes electricity to flow. He explained this result, called the photoelectric effect, by saying that light is made of tiny bundles of energy called photons. Photons hitting the metal knock particles called electrons away. Since electricity is simply moving electrons, he had solved the mystery of the photoelectric effect. In 1921, Einstein won the most famous prize in science, the Nobel Prize, for this work.

Another thing Einstein thought about was time. He said that time does not always flow at the same rate. He proposed that motion affects time. He called this idea the special theory of relativity.

Einstein then came up with his general theory of relativity. This theory has a new explanation for gravity. Einstein said that gravity comes from curves or dents in the fabric of space. Objects make dents in space the way a bowling ball makes a dent in a mattress. The Moon falls into the dent made by Earth and rolls around the Earth. Scientists later proved that the dent a star makes in space-time bends light as the light passes by.

Einstein changed physics by showing that new ideas could come just from thinking. Before Einstein, most new ideas in physics had come from experiments in the laboratory.

EINSTEIN AND ATOMIC ENERGY

Einstein also said that matter and energy are the same thing. He expressed this relation in a famous equation: E=mc². This equation says that energy (E) equals mass (m) times the speed of light squared (c²). Energy can therefore be changed into matter, and matter into energy. The ability to turn matter into energy led to the development of the atomic bomb and nuclear power.

FAME AND LATER YEARS

Einstein’s theories made him famous, even though few people understood them. He became a university professor and director of a physics institute in Berlin, Germany. After the Nazis rose to power in Germany, Einstein left. In 1933, he came to the United States, where he lived the rest of his life. Einstein died in Princeton, New Jersey, on April 18, 1955.

Einstein’s last great idea was that every force in nature is part of one master force. Physicists are still working on this idea, which they call the theory of everything.

Benjamin Franklin

Was Benjamin Franklin a famous scientist? Or was he an inventor? Was he a diplomat and a statesman? Or a printer and a writer? Franklin was not just one of these things—he was all of them!

EARLY LIFE

Benjamin Franklin was born in Boston, Massachusetts, on January 17, 1706. His father, Josiah, had 17 children. Franklin’s mother, Abiah Folger, was Josiah’s second wife.

Like many boys at that time, young Ben attended school for only a few years. At age 10 he began training in his father’s candle-making shop. Ben didn’t like the work. When he was 13, his father sent him to work with his older brother James.

LEARNING A TRADE

James Franklin taught his brother about the printing business. Ben learned to work the heavy printing press. He sold newspapers and even began writing articles. Franklin loved to read and study in his free time, teaching himself math, science, literature, and foreign languages.

In 1722, James Franklin was arrested for criticizing Boston’s leaders in his newspaper. Ben Franklin kept the paper running in his brother’s absence.

In 1724, 18-year-old Ben Franklin sailed to London, England. There he learned all he could about printing and publishing.

Franklin returned to America and settled in Philadelphia, Pennsylvania, in 1726. There he bought a small newspaper, the Pennsylvania Gazette. He married Deborah Read in 1730.

A MAN OF IDEAS

Despite his lack of schooling, Franklin had many ideas on how to improve people’s lives. For example, he organized one of the first public libraries in America. He also started the first fire department and one of the first hospitals in Philadelphia. He busied himself with plans to improve city streets and lighting.

Franklin wrote about improving education, and he helped found a school that became the University of Pennsylvania. In 1732, he began publishing a popular, witty advice book called Poor Richard’s Almanack. Franklin also founded the American Philosophical Society, based in Philadelphia, to discuss the latest scientific theories.

Around 1744, Franklin invented the Franklin stove, which provided more heat while using less fuel. A few years later, he began experimenting with electricity. In 1752, he invented a lightning rod, which keeps lightning from striking buildings and other structures. His scientific ideas and inventions became known in Europe as well as in America.

HOW FRANKLIN SERVED HIS COUNTRY

At the same time, Franklin added politics to his list of achievements. He wrote and published many articles about political issues. In 1754, the colonies sent representatives to a meeting to discuss how they should respond to the French and Indian War. There Franklin proposed his Albany Plan, calling for the colonies to keep their independence while working together on issues that affected all of them. His plan was rejected, but his vision of government would later influence the writing of the United States Constitution.

From 1757 to 1772, Franklin spent most of his time living in London. He represented the colonies in British politics. Franklin explained America’s views of British tax policies, such as the Stamp Act. His efforts helped get the hated Stamp Act repealed by the British government.

Like many Americans, Franklin felt torn between remaining connected to Great Britain and the desire for independence. He understood the growing anger of Americans over British taxes and other actions. Franklin returned to Pennsylvania in May 1775. The American Revolution (1775-1783) had begun a month earlier when fighting broke out in Massachusetts.

In 1775, the 70-year-old Franklin served as a representative at the Second Continental Congress, an early American governing body. He worked on many committees, including the committee that wrote the Declaration of Independence.

FRANKLIN AND THE REVOLUTION

Franklin spent most of the war years in Europe as a diplomat representing the American congress. He helped convince France to loan the Americans money to fund the war effort. Franklin’s humor and intelligence made him very popular in France. Eventually, France joined America in fighting—and defeating—the British.

As the war wound down, Franklin helped negotiate a peace treaty with Great Britain. The treaty, signed in 1783, recognized American independence and ended the long war.

STILL BUSY IN HIS EIGHTIES

Pennsylvania sent Franklin as a delegate to the 1787 convention that planned and wrote the United States Constitution. He was the convention’s oldest delegate.

Franklin remained interested in social causes in his old age. He served as president of the Pennsylvania Abolition Society, an antislavery group. He sent a petition to the United States Congress calling for an end to slavery.

Franklin died on April 17, 1790. His wisdom, wit, and hard work had served his country well.

Charles Darwin

Charles Darwin had no idea when he set off on a sea voyage to explore South America in the 1830s that he would set off a controversy that continues today. Darwin studied animals in isolated places. He thought that differences he saw in similar species (kinds) of animals meant that the animals had evolved, or changed over time. His important idea is called the theory of evolution by natural selection.

WHAT DARWIN OBSERVED

Charles Robert Darwin was born in Shrewsbury, England, on February 12, 1809. He came from a wealthy family and never had to work. He studied medicine and theology. In 1831, he had the chance to go on a scientific expedition. He sailed as a volunteer scientist aboard the HMS Beagle.

Everywhere the Beagle stopped, Darwin made observations of plants and animals. In the Galápagos Islands, Darwin noted that each island had its own form of tortoise, mockingbird, and finch. Each species on each island was slightly different. Darwin wondered if there were links between the similar species.

WHAT DARWIN DECIDED

For the next 20 years Darwin thought about what his observations might mean. He decided that the young of any species must compete for food in order to survive. Those with traits best suited to survival would grow up and reproduce offspring with those traits. Eventually, a new species would evolve. Darwin also thought that all species were descended from common ancestors. In 1859, he wrote a book called On the Origin of Species.

Many scientists did not believe his theory until modern genetics—the study of inherited traits—began in the early 1900s. Most attacks on Darwin’s ideas came from religious opponents. They thought that evolution denied the divine creation of human beings and made people and animals equal.

Darwin spent the rest of his life writing about his theory. He died on April 19, 1882.

Also in Encarta Kids

Copernicus

When Nicolaus Copernicus went to school, he learned that Earth was the center of the universe and that everything in the heavens revolved around Earth. The Sun and all the planets circled around Earth, he was told.

The Earth-centered theory taught to Copernicus had been developed 1,400 years before by an astronomer named Ptolemy, who lived in Alexandria, Egypt. Copernicus looked into Ptolemy’s system more carefully and came up with a different idea. He was sure that the Sun is the center of our solar system and that Earth and the other planets go around the Sun. He was right, of course. Today, we think of Copernicus as the founder of modern astronomy.

HIS LIFE AND CAREER

Copernicus was born on February 19, 1473, in Toruñ, Poland. His family was well-to-do. Copernicus went to the best schools. He studied medicine, law, and religion in Italy. He also became interested in astronomy. In 1503, he went back to Poland to work for his uncle. He also worked on his new theory about how Earth moves.

HIS SUN-CENTERED SYSTEM

Copernicus thought that Earth turns once a day and goes around the Sun once a year. Copernicus decided that the way Earth turns makes it look like the Sun, stars, and planets are going around the Earth.

In 1530, he wrote a book called On the Revolutions of the Celestial Spheres. The book was published in 1543, just before Copernicus died. Most astronomers and church officials thought his ideas were too radical. Some others, however, secretly thought he was right.

The Italian astronomer Galileo, German astronomer Johannes Kepler, and English physicist Sir Isaac Newton later did studies that supported the ideas of Copernicus. Not until the early 1700s, however, did most scientists agree that Copernicus was right.

Sun

The Sun is very important to you. You play in sunshine. You see in daylight. The Sun keeps you warm. Even ancient people knew the Sun was very important. They thought the Sun was a god. The ancient Greeks thought the Sun god drove a chariot across the sky every day. The ancient Egyptians thought the Sun god sailed a boat across the sky. Today we know that the Sun is a star. The Sun is the star at the center of our solar system. Earth and all the other planets orbit, or go around, the Sun. The Sun is very important to all life on Earth.

THE SUN IS A STAR

The Sun is a star—a ball of hot, glowing gas. It does not have any solid parts. It is made up mostly of hydrogen gas and helium gas. The Sun is huge compared with Earth. If the Sun were hollow, a million Earths could fit inside it. The Sun looks small only because it is far away. The average distance from Earth to the Sun is 93 million miles (150 million kilometers). You would have to go around the world more than 3,700 times in order to travel that far on Earth.

The force of Earth’s gravity holds you on the ground. The Sun’s gravity holds Earth and the other planets in their orbits. It holds asteroids, comets, and dust in orbit.

The Sun is one of about 400 billion stars in the Milky Way Galaxy. A galaxy is a large group of stars. The Sun and all the other stars orbit the center of the Milky Way.

ENERGY FROM THE SUN

Almost all the energy on Earth comes from the Sun. Heat from the Sun makes Earth warm enough for life. Plants use the Sun’s energy to live and grow. Plants give off a gas called oxygen. Animals eat the plants and breathe the oxygen. Animals need plants in order to live, and plants need the Sun.

You use plants to make heat and energy. You can burn wood from trees. You can burn fossil fuels called coal, gas, and oil. Fossil fuels formed deep underground from plants and animals that died millions of years ago.

The Sun’s energy can also do harm. Too much sunlight can burn your skin, causing sunburn. Harmful rays from the Sun can also cause a disease called skin cancer. Looking right at the Sun can harm your eyes. You need to be careful of the Sun.

THE CORE OF THE SUN

The center of the Sun is called the core. The core is extremely hot. The heat sends tiny bits of matter called atoms crashing into each other. The crashing atoms set off atomic or nuclear reactions. All the energy of the Sun comes from these nuclear reactions in its core. It takes a long time for the energy from the core to reach the surface of the Sun—about 170,000 years!

THE SURFACE OF THE SUN

The photosphere is the outer part of the Sun that we can see. Like the rest of the Sun, the photosphere is made of hot hydrogen and helium gas. Heat and light from the photosphere reach Earth. The temperature of the photosphere is about 9950° Fahrenheit (about 5500° Celsius).

Fountains of red-hot gas shoot up thousands of miles from the photosphere into the Sun’s atmosphere. Cooler dark spots called sunspots form on the photosphere.

Far above the photosphere is the corona. The corona is the top layer of the Sun’s atmosphere. The corona is so faint that the only time you can see it is when the light from the rest of the Sun is blocked. Astronomers use discs to block the light so they can study the corona. The temperature of the corona goes up to 4 million degrees Fahrenheit (2 million degrees Celsius). The corona trails off into space. Gases that blow off the corona are called the solar wind. The solar wind reaches far beyond Earth.

THE SUN IS A MAGNET

The Sun is a huge magnet. The magnetism of the Sun causes strange things to happen. Bright explosions called solar flares flash in the corona. The flares send gases looping out into space. Sometimes there are huge explosions in the corona that send billions of tons of material into space. The flares and explosions can cause magnetic storms on Earth. These storms cause problems for satellites and cell phones.

HOW DID THE SUN FORM?

Astronomers believe our solar system formed about 4.6 billion years ago from a swirling cloud of dust and gas. The Sun formed first at the center of the cloud. Then the planets formed from dust and gas going around the Sun.

Someday the Sun will burn out. It will use up all the fuel in its core. You don’t need to worry. Astronomers say that the fuel will last several billion more years.

Stars

Go outdoors at night and look up at the sky. There are twinkling points of light everywhere. You are seeing thousands of stars that are millions of miles away. The stars look tiny because they are so distant. But if you could see those stars up close, you would see huge balls of fire.

The closest star to you on Earth is the Sun. The Sun is a star at the center of our solar system. Our Sun is about 4.6 billion years old. There are stars that are older or younger than our Sun. There are stars that are much bigger. There are stars that have exploded and stars that are just being born.

WHAT IS A STAR?

A star is a big ball of hot, glowing gas. The gas is mostly hydrogen and helium. Stars give off heat, light, and other kinds of energy.

A star has several layers. The part at the center of a star is called its core. A star shines because of its core. The core is so hot and tightly packed that atoms crunch together. Atoms are tiny bits of matter much too small to see. Hydrogen atoms crunch together and become helium atoms. This is called nuclear fusion. Nuclear fusion gives off enough energy to make the stars shine.

GROUPS OF STARS

Stars are part of groups called galaxies. Our Sun is in the Milky Way Galaxy.

People in ancient times grouped stars by patterns they thought they saw in the sky. The patterns are called constellations. They thought the patterns looked like people, animals, or objects. The Big Dipper is a constellation of seven stars in the shape of a dipping ladle. Astronomers map where the stars are in the sky using the constellations.

WHAT COLOR ARE STARS?

Stars come in different colors. They can be deep red, orange, yellow, white, or even blue. The color of a star depends on how hot the star is. The coolest stars are reddish and the hottest stars are bluish.

It is hard to imagine how hot a star can be. The temperature at the surface of red stars is about 5400° Fahrenheit (about 3000° Celsius). Yellow stars have surface temperatures about 11,000° Fahrenheit (about 6000° Celsius). Our Sun is a yellow star. White stars are about 18,000° Fahrenheit (about 10,000° Celsius)!

A star looks as if it is just one color. Starlight, however, is made up of many colors. Light from our Sun has all the colors of the rainbow. Astronomers study the light of other stars. Patterns in the light can tell astronomers what the stars are made of and how hot they are.

HOW BRIGHT IS A STAR?

Some stars in the sky look brighter than others. Some stars really are brighter. Other stars just look brighter because they are closer.

Some stars are not nearly as bright as the Sun. Other stars are as much as 500,000 times brighter.

HOW BIG IS A STAR?

The Sun is huge compared to Earth. If the Sun were hollow, a million Earths could fit inside it!

Astronomers compare the size of other stars to the size of the Sun. For example, a star called Betelgeuse is about 1,000 times bigger than the Sun.

WHERE DO STARS COME FROM?

Stars are born from swirling clouds of gas and dust. Gravity pulls the gas and dust together. The gas and dust form a spinning ball. As it spins, it gets hotter. The gas and dust get tightly packed. Finally, nuclear fusion begins and the star starts to shine.

A STAR’S LIFE

There are different stages in a star’s life, just as there are different stages in the lives of people. Right after a star is born it starts to get smaller. After a million years of shrinking, the star enters the main sequence of its life.

After about 10 billion years, the star’s core runs out of fuel. The star grows many times larger than it was during the main sequence. At this stage the star is called a red giant. What happens next depends on the size of the star.

GIANTS AND DWARFS

Medium-sized stars like our Sun become white dwarfs. White dwarfs can explode. The outside gas layers blow off and make clouds called nebulas. The core keeps shrinking. A spoonful of white dwarf core could weigh more than a dump truck. After several billion years, the star loses all its energy and becomes a cold black dwarf.

Really big stars become supergiants. Supergiants become supernovas, which are big exploding stars. The explosion sends gas and dust into space to make new stars. The core gets packed tighter and tighter. Some cores then turn to iron and become neutron stars. Some supernova cores turn into black holes, which swallow everything around them in space. Not even light can escape from a black hole.

COULD ASTRONAUTS VISIT A STAR?

Stars beyond our solar system are too far away for a spacecraft to reach. The closest star is Proxima Centauri. It is more than 4 light-years from Earth. A light-year is the distance light travels in a year, about 6 trillion miles (about 9 trillion kilometers) Most stars are much farther away than Proxima Centauri. No spaceship can travel fast enough to reach even the nearest star during an astronaut’s lifetime. It takes billions of years for even light to reach the most distant stars.

Telescopes

Telescopes help us see things that are far away. They make distant objects look bigger. Using telescopes, astronomers have discovered thousands of stars, planets, moons, and many other extraordinary objects, such as black holes.

The most common type of telescope is the optical telescope. This kind of telescope gathers light from distant objects.

HOW DO OPTICAL TELESCOPES WORK?

Imagine having eyes as big as your fist. You’d look funny, but more light would enter your eyes. You would be able to see better. Telescopes bring extra light to our eyes. They effectively make our eyes bigger. Distant objects appear larger when you look through a telescope, and you can see more detail.

A refracting telescope is the simplest type of optical telescope. It is made up of two lenses. These lenses are similar to the lens in a magnifying glass. A reflecting telescope has a lens and a dish-shaped mirror. The mirror collects and focuses (concentrates) light.

A telescope’s eyepiece can be replaced by a camera. Then the image from the telescope is recorded on film or as a digital image.

GIGANTIC OPTICAL TELESCOPES

The bigger a telescope’s main lens or mirror, the more light the telescope gathers. The more light the telescope gathers, the more detail it shows, and the more distant the objects that you can see through it.

Astronomers use huge telescopes housed inside buildings called observatories. These telescopes have mirrors as large as 26 feet (8 meters) across. They gather enormous amounts of light.

BIG TELESCOPE WOES

Gigantic telescope mirrors are hard to build because they bend under their own weight. When a mirror bends, it makes a blurry image. One way to keep a giant mirror from bending is to divide the mirror into smaller sections. Another way to avoid huge mirrors is to use computers to combine images from several telescopes. The Very Large Telescope in Chile, for example, has four telescopes with 26-foot (8-meter) mirrors. Together they gather the same amount of light as a telescope with a 52-foot (16-meter) mirror.

Air causes another problem for telescopes. The air low in Earth’s atmosphere swirls about. This movement bends the light coming down from space just a bit, making the images we see through telescopes appear slightly blurry. To reduce this effect, large telescopes are often built on high mountains. This puts them above much of the air in the atmosphere. Many modern telescopes also have flexible mirrors. The shape of their mirrors can be automatically adjusted hundreds of times a second to adjust for the swirling atmosphere and keep the image sharp.

TELESCOPES THAT SEE INVISIBLE RADIATION

Optical telescopes are only one type of telescope. Astronomers also use telescopes that detect other kinds of electric and magnetic rays from space, such as X rays and radio waves. Our eyes cannot see these rays. Some objects in space aren’t bright enough to be seen with visible light. We wouldn’t know they exist without telescopes that can detect other types of radiation.

A radio telescope, for example, detects radio waves given off by planets, stars, and other objects in space. It has a huge dish that collects the radio waves and focuses them on to an antenna in the center of the dish. The dish can be turned to point at any part of the sky. The antenna turns the radio waves into electrical signals that astronomers record and study.

TELESCOPES IN SPACE

Several space telescopes are in orbit around Earth, beyond the atmosphere. From there, they have a perfectly clear view into space. This means they can see much more detail on distant objects.

Some types of radiation, such as ultraviolet light, X rays, and gamma rays cannot pass through Earth’s atmosphere. Telescopes that detect these types of radiation must be launched into space.

THE FIRST TELESCOPES

We do not know exactly who invented the telescope, but we do know it was invented in Holland at the beginning of the 17th century. The first person to look into space through a telescope was the Italian scientist Galileo. He was the first to see moons orbiting Jupiter, Saturn’s rings, and mountains on the Moon.

Television

You probably have a favorite television show. Maybe you have more than one favorite TV show. Did you ever wonder where your favorite shows come from? Did you ever wonder how they get to the TV set in your home?

WHERE DO TV SHOWS COME FROM?

Some TV shows are made in TV studios. Some of these shows are broadcast live—that is, as they are being made. Some shows are taped in the studio. The tape gets played on TV later on.

Other TV shows are made outside of studios. Baseball and football games and other sports events come from stadiums. Some parts of news programs are broadcast “on the scene.” TV reporters go to the scenes of accidents, floods, and fires and describe what is happening.

Shows in studios are made on sets. Sets for plays or soap operas can look like living rooms or kitchens. Sets for talk shows might have a desk for the host and chairs for the guests. Bright lights shine down on the sets.

HOW ARE TV PICTURES MADE?

A TV picture starts with a TV camera. Some TV cameras are big and some are small. The cameras in TV studios are big. Camera operators roll the big cameras around on wheels. There are usually several big cameras in a TV studio. Cameras used outside a TV studio are smaller. TV camera crews take the smaller cameras to news and sports events.

Some cameras send out live pictures to your TV set. Some cameras make videotapes that get played later on a television program.

All TV cameras need electricity to work. A camera operator points the camera at a scene. The camera picks up light from the scene. It changes this light into an electric signal called the video signal. A microphone changes the sound of people talking or music playing into an electric signal called the audio signal.

TV cameras do not snap pictures the way an ordinary camera does. Parts inside a TV camera scan, or sweep over, the scene and trace a series of thin, horizontal lines, one below the other. A TV camera scans a whole scene much faster than you can blink. Lines from the scans go together to make a picture.

THE TV CONTROL ROOM

The pictures and sound from the TV cameras and microphones go to a control room. Every television station has one or more control rooms. TV cameras in a studio can send live pictures to the control room. The control room is full of dials, switches, and small TV screens. There are screens that show pictures from each TV camera in the studio.

Producers and directors work in the control room. They make sure that the best pictures with the best views go to your TV screen at home.

People who work in control rooms also use taped pictures to make programs. They use computers to put together the best taped scenes.

HOW DOES THE SHOW GET TO YOUR HOME?

The picture and sound signals go from the control room to a transmitter. The transmitter makes the signals stronger and sends them to a transmitting antenna. This antenna is very tall. It changes the electric signals into invisible television signals that go through the air. The television signals go out from the antenna in all directions.

TV signals can get to the TV set at your home in several ways. They can go through the air to an antenna on your roof. The antenna picks up the signals and sends them through wires to your TV set. The signals could go to a cable TV company. The company sends the signals through a cable to your home. The TV signals could come right to your house from a satellite circling high above Earth. A satellite dish outside your home can pick up the TV signals and send them over wires to your TV set indoors.

HOW DOES YOUR TV SET WORK?

Your TV set changes the television signals back into pictures and sound. Your set picks up the thin lines that the TV camera scanned. Your set uses parts called electron guns to “paint” a picture on the TV screen one thin line at a time. The lines get painted from top to bottom.

A color TV set uses three electron guns to beam out three colors—red, green, and blue. These three colors make all the colors you see on your TV screen. The beams scan fast enough to paint a picture on your screen 30 times a second.

OTHER WAYS TO USE TELEVISION

Television can do many things. TV cameras can be sent to places that are difficult or dangerous for people. They can travel to outer space. Spacecraft carry TV cameras to other planets. The cameras send back pictures that let us see what other planets look like.

TV cameras on robot submarines can go deep down in the sea. Doctors use tiny TV cameras to see inside the human body.

WHEN WAS TV INVENTED?

Inventors made the first TV pictures in the 1920s. Television stations started broadcasting the first regular TV shows in the 1940s. The first TV sets had small screens. The first TV sets showed black-and-white pictures.

Television sets have gotten better and better. Most TVs sold today show color pictures. TV screens have gotten bigger and bigger. TV sets have gotten thinner. Plasma TV sets are so thin that you can hang them on a wall.

Cartoons and Comics

Do comic strips in the newspaper make you laugh? Perhaps you prefer colorful comic books about the adventures of superheroes? Or maybe you like cartoons on television or animated movies? Whatever your choice, chances are you enjoy some form of cartoons and comics.

WHAT ARE CARTOONS?

The word cartoon once meant something entirely different than it does today. It was used to describe a sketch made by an artist to prepare for a painting or other work. In the 1840s, the English magazine Punch published cartoons that made fun of artwork planned for public buildings in London. Since then, “cartoon” has generally meant a drawing intended to be funny or to make a point.

Many newspapers and magazines have editorial cartoons, which express an opinion. Such cartoons often use caricatures, or exaggerations of a person’s features, to make fun of figures like politicians. Gag cartoons tell a joke. Editorial and gag cartoons usually have a single panel, a box with a border around it. They may include words, but sometimes they show only a drawing.

CARTOONS THAT MOVE

Cartoons that are animated, or appear to move, have been around for centuries. The first ones were called flipbooks. They were made of pages of drawings. Each drawing was slightly different from the last. People flipped the pages with their thumb. The characters appeared to move.

Early animated movies were like flipbooks. They were costly and difficult to make. Each picture had to be drawn separately by hand. A seven-minute cartoon used over 10,000 drawings! Eventually, new methods were invented that made cartoons easier and cheaper to make. Today, animated cartoons are a big part of television. Have you ever watched Scooby Doo, The Simpsons, or SpongeBob SquarePants?

WHAT ARE COMICS?

Comics, or comic strips, are cartoons with several panels that tell a story. You can find comic strips in the funny papers, a section of the daily newspaper. In some comics, each daily strip tells its own story. In others, each strip is part of a continuing story. Popular comic-strip characters include Charlie Brown, his dog Snoopy, and their friends in Peanuts, and the fussy cat in Garfield.

The first comic strips appeared in American newspapers in the 1890s. One of the earliest was Hogan’s Alley, by Richard Outcault. It featured a bald boy in a yellow nightshirt called the Yellow Kid. By the early 1900s, comic strips were a part of most American newspapers.

COMIC BOOKS

The first comic books were just collections of newspaper comic strips. Comic books with original material began to appear in the 1930s. They could tell longer and more detailed stories than newspaper strips. Comic books became widely popular beginning in 1938 with the first appearance of the superhero character Superman.

New superheroes soon appeared in other comic books, including the Flash, Wonder Woman, and Captain Marvel. Comic books in the 1960s introduced a whole new set of superheroes, such as X-Men, Spider-Man, and the Fantastic Four. These newer superheroes all had special powers, but they had problems in life like everyone else.

TAKING COMICS SERIOUSLY

For many years, many people looked down on comics as silly stories and a waste of time. This attitude changed. In the 1980s and 1990s, comics began attracting lots of collectors and even scholars who studied them. Comic collectors hold big conferences in the United States and Canada to buy, sell, and trade comics.

Today, some comic books, called graphic novels, are considered serious literature. In 1992, the graphic novel Maus, by Art Spiegelman, won a prestigious award called the Pulitzer Prize.

Movies

What is your favorite movie? Maybe you like cartoon-like movies. Maybe you like a movie that is full of action. Movies are a wonderful kind of make-believe.

A movie is a series of pictures. Each image is a still photograph, just like a picture you take with a regular camera. But the pictures flash by so fast in a movie that the images blend together and overlap. As a result, you see horses run, people talk, cars plunge over mountainsides, and other kinds of motion. That’s why movies are sometimes called motion pictures. Movies are also called films because they are photographed, or filmed.

HOW DO THEY MAKE CARTOONS?

Cartoons are called animated films. Artists draw the scenes. They draw the background and the characters. Each drawing of the character is slightly different. For example, the legs are in different places if the character is running. A special camera takes pictures of each scene the artist has drawn. When the pictures are played back, it looks like the character is running. Making drawings that seem to move is called animation.

Some enjoyable animated films include Snow White and the Seven Dwarfs (1937), Beauty and the Beast (1991), The Lion King (1994), and Finding Nemo (2003). In some films, there are both animated characters and human actors, as in Space Jam (1996). Space Jam stars Bugs Bunny and basketball star Michael Jordan.

WHO WORKS ON MOVIES?

Many different people work on a movie. The producer finds money to pay for the film, hires people to make the movie, and gets the movie to theaters. The director imagines how the film should look and guides the actors and the crew as they make the movie. Assistants help the producer and the director.

Screenwriters write an original story for the movie, or they work with a story told in a book. Actors play characters in the story. A music composer writes background music for the film.

Most members of the movie crew work behind the scenes. Designers make the sets and costumes. The camera crew runs the cameras that film the movie.

Dozens of short scenes have to be put together after the filming is done. That is the job of the film editors. Sound editors add background noises, such as honking horns in a scene on a busy street. In action films, stuntmen and stuntwomen often fill in for the actors and perform dangerous moves that could lead to injury.

HOW DO THEY SHOOT A MOVIE?

Lots of work has to be done before the filming begins. The producer and director plan how and when they will film each scene.

A movie is filmed scene by scene, and a scene is filmed shot by shot. The scenes are not usually filmed in the order that you see them in the movie. Sometimes the weather is bad and an outdoor scene cannot be filmed. Big, fancy sets take a long time to build. Scenes using these sets are often shot later even though you may see them at the beginning of the film.

When it is time to film a scene, the designers get the set ready. The actors run through their lines and movements. The director of photography arranges the lights. The camera operator checks camera angles for the shot. The sound crew sets up microphones.

The cameras roll. Each filmed shot is called a take. The director may ask for many takes before he or she is satisfied with the scene.

WHAT ARE SPECIAL EFFECTS?

Special effects create the illusion of things that moviemakers could not possibly shoot. Special effects include small models of huge scenes, cleverly designed sets, and computer-generated images. Moviemakers use these to film scenes and places that do not exist. They might use a small model of a large building to stage and film the building falling down.

Some sets for the movie Titanic (1997) had to look like a sinking ocean liner. The moviemakers could not film the inside of a large ship sinking. So the set designers built the ship’s grand staircase and dining saloon over a huge tank that held 5 million gallons (19 million liters) of water. They lowered the sets into the water tank to make it look as if the rooms were sinking.

COMPUTERS AND SPECIAL EFFECTS

Films can be digitized, or turned into computer files. Moviemakers can then change the images any way they want. They can use computers to make new images. Dinosaurs made by computer looked like they were charging toward people in Jurassic Park (1993).

Computers can even make images of actors. Many images in Titanic, including crowds of people on the ship, were actually made by computer. In The Matrix (1999), computers were used to make the actors look as if they were fighting while floating in the air.

Medical Care

Do you ever visit the doctor? Sometimes people visit doctors because they are not feeling very well. Sometimes people visit doctors for a physical examination, or checkup. Visits to doctors are part of medical care. Many other people also contribute to medical care.

WHAT DO DOCTORS DO?

Doctors try to diagnose, or figure out, what makes people sick. If you have a sore throat or a bad cough, the doctor examines you with a stethoscope. The doctor uses the stethoscope to listen to your heartbeat and to the sound your lungs make when you breathe. The doctor looks into your nose, ears, and throat and may order some laboratory tests. Then the doctor diagnoses your problem. Sometimes the doctor tells you your body will get well on its own. Sometimes the doctor orders drugs to help you.

Some doctors are specialists. They have extra training. Different kinds of specialists treat heart disease, cancer, arthritis, and other diseases. Some specialists only treat children or old people. Other specialists do surgery. Surgeons can take out diseased organs and even replace hearts, lungs, and livers. Some surgeons fix broken bones and replace knees and hips.

WHAT DO NURSES DO?

Many other people besides doctors provide medical care. Nurses, for example, are very important to medical care.

Have you had your tonsils out? Did you go to the hospital? If you did, nurses probably took care of you. Nurses care for sick patients.

Nurses help doctors do examinations and give treatments. Special nurses called nurse practitioners do many things that doctors once did. They diagnose what is causing an illness and prescribe drugs. Surgical nurses help with operations. Nurse-midwives deliver babies and care for mothers.

WHAT DO OTHER MEDICAL WORKERS DO?

If you have a sore throat, your doctor may take some mucus from the inside of your throat. Medical laboratory technicians study this material to see if there are disease-causing germs. Laboratory technicians also examine blood samples for signs of illness.

When people fall and hurt themselves, medical imaging technicians take X rays of the bones. The pictures show if any bones are broken. Other medical imaging tools can show if there are any clumps of abnormal cells called tumors inside the body.

Physician’s assistants sometimes work in places where there is no doctor nearby. They do many of the things that doctors do. They also talk to a physician by telephone or e-mail. Dentists look after your teeth. Psychologists and psychiatrists work on mental health.

WHERE DO YOU RECEIVE MEDICAL CARE?

You may have visited the doctor in an office. Most doctors share an office with other doctors. Some doctors work in a clinic, a hospital, or a big medical center. Nurses work in many of the same places as doctors.

You may have seen a doctor in a hospital. If you broke a bone, you probably went to the emergency room at a hospital for medical care.

WHAT DO MEDICAL RESEARCHERS DO?

You never see some of the people who take part in your medical care. Medical researchers work in research laboratories. They have made discoveries that saved millions of lives.

Medical researchers try to find the cause of diseases. Then they try to find treatments to cure or prevent the disease.

One of the greatest medical research discoveries was that bacteria, viruses, and other microscopic germs cause infections. French scientist Louis Pasteur and German scientist Robert Koch in the 1800s showed that germs spread disease. Making sure people had germ-free water and food stopped deadly diseases such as cholera and typhoid.

Researchers in the mid-1900s discovered antibiotics, drugs that cure infections by killing bacteria. Researchers also found vaccines that protect against smallpox, polio, and other diseases caused by viruses. Vaccines work by getting the body ready to kill these germs if they attack.

BEFORE MODERN MEDICAL CARE

People long ago thought evil spirits caused disease. Prehistoric people danced and made magic charms to drive the spirits away. Sometimes they cut a hole in the sick person’s head to let the evil spirit out. Other ancient peoples thought that illness was a punishment from the gods. The ancient Greeks were the first to understand that evil spirits and gods do not cause disease.

Hippocrates, called the father of medicine, and another Greek physician named Galen believed that disease was caused by an imbalance of four body fluids. They called these fluids humors. Until the mid-1800s, doctors used the ideas of Hippocrates and Galen to treat illnesses. Many of their ideas were wrong, however.

Until the mid-1800s, doctors could carry all their instruments and medicines in one little black bag. There were few cures for serious illness. Doctors used bleeding as a treatment for almost all illnesses. The doctor cut a blood vessel and drained out some blood. They thought this brought the humors back into balance. Doctors also gave powerful drugs to clean harmful poisons from the body.

Doctors performed surgical operations. Most operations in the 1800s were amputations of arms and legs. About half of the surgical patients died from infection. Operating rooms were filthy, and surgeons did not even wash their hands. After germ theory was discovered by Pasteur and Koch, British surgeon Joseph Lister showed how to make operating rooms germ-free.

Operations once had to be done quickly because there was no way to put patients to sleep. A doctor and a dentist first used ether in the 1840s. Ether and other drugs let surgeons put patients to sleep during operations. These drugs, called anesthetics, reduce pain during surgery. With anesthetics, surgeons learned how to perform longer, more complicated operations to save lives.

WHAT’S NEXT?

Medical researchers are now looking for ways to cure diseases caused by problems with genes. Genes are the basic units of heredity. Through genes, parents transmit traits such as eye color to their children. Genes also give instructions to our body’s cells. Genes are made of DNA. If something goes wrong with its DNA, the gene can make trouble. Some problems with genes appear at birth. Others occur later on. Doctors do not yet have good treatments for diseases caused by genetic problems.

Doctors and researchers are also working to prevent diseases by helping people lead healthy lives. They tell us to eat nutritious food, exercise, avoid smoking, and have regular physical checkups.

Literature

Novels, poems, plays, folktales, and myths—all these are literature. Literature exists in all cultures. By writing literature, people communicate ideas and feelings. By reading literature, we share these ideas and feelings. Literature lets us visit places and people we might otherwise never know. And we don’t even have to leave our chairs. Let’s take a look at different kinds of literature.

WHAT IS FICTION?

Many people like to read fiction—stories that writers make up in their imagination. Novels and short stories are fiction. Even though the characters and events in fiction are imaginary, a good writer can make us believe they are real.

A novel is usually a long book. Its plot (main story) is packed with twists and turns, and it may have several subplots (smaller stories within the main story). A short story tells only one story and is shorter than a novel.

Fiction doesn’t have to describe the world we know. Many people read fiction to escape everyday life. Fiction can offer a substitute life, perhaps an adventure or a romance. Reading about other people’s struggles, hopes, and decisions can sometimes give us a better understanding of our own life.

Some people like scary or spooky tales. Others like to read science-fiction stories that imagine life on other planets or life in the future. Readers also enjoy unraveling the puzzles of mystery and spy fiction. Fantasy fiction describes magical or supernatural events. Historical fiction takes us back to the past. Fiction has something for everyone.

WHAT IS POETRY?

Poetry, like all literature, makes use of language. But poetry uses words in special ways. It emphasizes their sounds and rhythms. It makes patterns of sound and rhythm. Most of the patterns in poetry come from repetition.

Rhyme is a pattern that repeats sounds. The line “You must never go down to the end of the town” rhymes the repeated sound in the words down and town. Notice the rhythm of that line, too. Read it out loud and see which words you stress most.

Rhythm is also a pattern. Poets produce rhythm by repeating words, syllables (parts of words), or beats. English writer A. A. Milne repeated words and beats in the poem “Disobedience,” which begins

James James
Morrison Morrison
Weatherby George Dupree

In “Jabberwocky,” English writer Lewis Carroll shows that we don’t even need to understand the words of a poem to enjoy their sounds and rhythms.

’Twas brillig, and the slithy toves
Did gyre and gimble in the wabe;
All mimsy were the borogoves,
And the mome raths out grabe.

Poetry also creates pictures in our minds. It helps us see or imagine things in new ways. American poet Carl Sandburg wrote, “The fog comes in on little cat feet.” Can you picture it? By comparing fog to a cat, Sandburg is telling us that fog moves silently and stealthily, just like a cat. Poets like to make comparisons to help us see things.

WHAT IS DRAMA?

Drama is literature meant to be acted out. Drama tells a story through its characters. The characters, played by actors, speak words called the dialogue. The plot, or story, is told through the dialogue.

Since ancient times, the two main kinds of drama have been tragedy and comedy. Tragedy deals with serious issues. The main character usually goes through some kind of struggle, perhaps in trying to decide the right way to behave in a difficult situation. A tragedy generally ends unhappily, sometimes with a disaster or the death of an important character.

Comedy deals with the lighter side of life. It pokes fun at people and usually ends happily. Comedy can be witty and wise, or silly and full of ridiculous situations.

WHAT ARE FOLKTALES AND MYTHS?

Folktales include fairy tales, animal tales, and tall tales. Folktales that involve unlikely events, magic, and supernatural beings are called fairy tales. Animal tales are stories about animals that usually have been given human speech and human traits. When animal tales include a moral or lesson about behavior, they are known as fables. Tall tales are wild exaggerations. They tell about events that couldn’t possibly have happened.

Myths are generally stories about gods and goddesses. They try to explain how the world and all the things in it were created.

WHAT IS NONFICTION?

Have you ever been asked to write a report on spiders, Thanksgiving, or pioneer life in the West? That is nonfiction writing. Nonfiction is based on information that is real and not made up in the imagination of the author. Nonfiction includes biographies, history, and science writing. It includes books on how to do something and how to improve our lives.

GREAT LITERATURE LASTS

Writing changes over time to reflect the needs of each generation. But literature also explores basic human feelings, such as greed, love, and ambition. These feelings have changed very little over time. They have always inspired good stories told well. For this reason, we can still enjoy great literature of any age for its story and expressive language.

Harry Potter

So, who’s your favorite? Hogwarts Headmaster Albus Dumbledore? Whiz-kid spellcaster Hermione Granger? The massive Rubeus Hagrid, Keeper of Keys and Grounds? Or Professor of Transfiguration Minerva McGonagall?

Or maybe you like Harry Potter the best. If you do, you’re not alone. Kids all over the world (and adults, too!) love Harry Potter and the books that tell of his adventures.

THE BOY WIZARD

Maybe you haven’t read Harry Potter’s adventures. If not, then let’s quickly introduce him.

Harry Potter is an unhappy 11-year-old. He lives with his Aunt Petunia and Uncle Vernon Dursley and their awful son Dudley.

Harry doesn’t know it, but he’s a wizard! His mother was a witch and his father was a wizard. Both died fighting the evil wizard Voldemort when Harry was just a baby. Harry was hidden with the unmagical Dursleys to protect him from Voldemort.

Harry’s adventures begin when he is accepted to Hogwarts School of Witchcraft and Wizardry. There, he meets adults like Headmaster Albus Dumbledore and Groundskeeper Rubeus Hagrid. He also befriends schoolmates like Hermione Granger and Ron Weasley, and meets rivals like Draco Malfoy. He learns magic and how to play Quidditch, a game a little like soccer that is played on flying broomsticks.

The Harry Potter novels tell the adventures of Harry at Hogwarts. Each book covers one school year in Harry’s life, starting at age 11.

THE AUTHOR

The creator of the Harry Potter novels is writer J. K. Rowling. The J. K. stands for Joanne Kathleen. Rowling was born in a small town in southern England. She studied languages in college. But she always wanted to be a writer. After finishing college, she lived in Paris, France, and in Portugal. When she returned to the United Kingdom, she began to think about Harry Potter.

Rowling got the idea for the first Harry Potter book while on a train journey to London. Like many writers, her first book was rejected by a number of publishers. But Rowling persisted and eventually found a publisher for Harry Potter and the Philosopher’s Stone. The book appeared in the United Kingdom in 1997.

SUCCESS STORY

Harry Potter and the Philosopher’s Stone was a big success. It won prizes for children’s literature in the United Kingdom. It was then published in North America with a slightly different title, Harry Potter and the Sorcerer’s Stone. The story was very popular there, as well.

Other books about Harry followed: Harry Potter and the Chamber of Secrets, Harry Potter and the Prisoner of Azkaban, Harry Potter and the Goblet of Fire, Harry Potter and the Order of the Phoenix, and Harry Potter and the Half-Blood Prince. The novels have been translated into more than 30 languages and have sold millions and millions of copies. The arrival of a new Harry Potter book is a worldwide event!

Some of the books have also been made into movies. After a long search, the filmmakers found Daniel Radcliffe to play the part of Harry in Harry Potter and the Sorcerer’s Stone. The movies have been a big success, too.

William Shakespeare

No author is quoted more often than William Shakespeare. His is the most famous name in all of English literature. What makes him so great?

EARLY LIFE

Shakespeare was born in 1564, in Stratford-upon-Avon, a prosperous town in England. His local grammar school had a demanding curriculum. At age 18, he married Anne Hathaway. They had a daughter, Susanna, and twins—Hamnet and Judith. At some point, Shakespeare left Stratford for London, to work in the theater.

PLAYWRIGHT IN LONDON

Shakespeare made his reputation with 38 glorious plays. He wrote about two plays a year, while living in London. He never published the plays, but he saw them performed at the Globe and other London theaters.

Shakespeare’s plays were well liked by audiences. But we know little about his life in London. Later, he retired in Stratford as a prominent citizen. He died in 1616. Two actors saw that his plays were printed. A collection called the First Folio came out seven years after his death.

A WRITER FOR ALL TIME

Shakespeare was a fabulous storyteller. His plays entertained audiences. Most people of his time considered his plays merely popular entertainments, much as we think of the movies today.

Shakespeare was also a profound thinker. He created a variety of true-to-life characters in his plays. These characters seem real because Shakespeare presented their viewpoints so well. The richness of his language is amazing. He even invented many words and phrases that are now common, including leapfrog, lonely, and watchdog.

Shakespeare’s plays reflect many aspects of human life. He wrote delightful comedies, such as A Midsummer Night’s Dream, Much Ado About Nothing, and As You Like It. He wrote plays about England’s kings that teach history in an entertaining way. The great tragedies explore flaws in human nature. These plays include Hamlet, Romeo and Juliet, Othello, King Lear, and Macbeth. In his spare time, he wrote poetry. His 154 sonnets are among the most famous love poems of all time.

Circus

Look to your left! Ten elephants are walking around a ring on their hind legs! To the right, three small cars loaded with clowns are driving around in circles! Between the elephants and clowns, high above the floor, a woman swings and spins in the air!

You guessed it—the circus is in town!

WHAT IS A CIRCUS?

A circus is a show that includes a variety of entertaining acts. It’s usually a traveling show that moves from town to town. Circuses perform in an arena or under a big tent. Some circuses stay in one place. The famous Moscow State Circus in Russia has performed in Moscow for many years.

Most circus acts take place in a round area called a ring. Small circuses have one or two rings. The largest circuses have three rings. Perhaps the most famous circus in the world is the Ringling Brothers and Barnum & Bailey Circus. It was the first-ever three-ring circus, with acts going on at the same time in every ring. It still calls itself the “Greatest Show on Earth.”

What will you see at a circus? Well, you might see acrobats, jugglers, and tightrope walkers. You might see elephants parading, tigers jumping through flaming hoops, or skilled horseback riders performing tricks. You certainly will see clowns, and lots of them! Throughout the show, a circus band plays lively music.

THE RINGMASTER

The ringmaster is the person in charge of the circus floor. He or she is your host. The ringmaster might wear a tuxedo and a top hat. He might even sing and dance. But whether it’s a one-, two-, or three-ring circus, the ringmaster will introduce you to all the exciting acts you’ll see.

ANIMAL ACTS

Most circuses feature animal acts. In fact, the modern circus began with an animal act back in the 1700s. A former soldier named Philip Astley performed tricks on horseback in England. His style of show, which became known as Astley’s Circus, was a hit. Circuses soon spread through Europe and then to the United States.

Over time, circuses added many other animal acts. Today, you might see bears, lions, tigers, chimpanzees, or dogs performing tricks at the circus. At the Moscow State Circus, you can even see trained porcupines!

One of the most popular circus animals is the elephant. These intelligent and playful animals can learn many tricks. They are so sure-footed they can balance on one foot.

ACROBATS ABOVE AND BELOW

Circuses usually have acrobats—people who perform gymnastic and balancing stunts. Some acrobats perform on the ground and some perform high in the air. On the ground you’ll see acrobats tumble and jump over one another. You’ll see them stand on each others’ shoulders to form huge human pyramids. Acrobats on horseback perform amazing and dangerous tricks while their horses trot around the ring.

In the air you’ll see the acrobats on the trapeze, a swing high above the ground. Trapeze artists do daring midair spins and jump from one swing to the next. Sometimes, members of a trapeze team throw each other through the air!

Tightrope walkers also perform their exciting acts in the air. They walk, do somersaults, and even ride bicycles—all while balancing on a thin wire high above the floor.

SEND IN THE CLOWNS!

What’s a circus without clowns? Every circus has them. Dressed in funny costumes and makeup, clowns entertain the audience between the other acts. Clowns play pranks on each other and perform comic stunts, such as tripping over their own shoes. Some clowns are skilled acrobats.

How do you learn to be a clown? Believe it or not, you go to special clown schools! The most famous is the Ringling Brothers and Barnum & Bailey Clown College in Venice, Florida. Since 1968, more than 1,200 clowns have graduated from the school.

Muhammad Ali

When Muhammad Ali was 12 years old, someone stole his bicycle. It was a shiny new bike, a birthday present. Ali was very angry. He told a police officer he wanted to punch the person who stole it. The officer suggested that he back up those “fighting words” by learning how to box.

During the next 25 years, Muhammad Ali would become one of the top athletes and best boxers of the 20th century. He won a gold medal at the Olympic Games. He went on to earn the title of world heavyweight boxing champion three different times. His fights were major events watched by millions of people around the world.

THE YOUNG CASSIUS CLAY

Muhammad Ali was born in 1942 in Louisville, Kentucky. His parents named him Cassius Marcellus Clay, Jr. They named their son after a Kentucky statesman who had fought against slavery in the 1800s.

Young Cassius Clay quickly made his mark in the boxing ring. He turned professional after winning a gold medal in the Olympic Games in 1960. Four years later, he knocked out Sonny Liston to earn his first world heavyweight champion title.

After winning the title, Clay converted to Islam. This religion follows the teachings of the prophet Muhammad. When Clay converted, he took a new name, Muhammad Ali.

A CHAMPION IN PRISON

In 1967, Ali was called on to join the United States Army. The country was fighting the Vietnam War at the time, and young men were being enlisted to take part. But Ali refused to go. He said his religion taught him to oppose all wars.

Ali was sentenced to prison, fined, and stripped of his boxing title. Ali fought his conviction, but he did not regain the right to box professionally for 3½ years.

THRILLING FIGHTS

In 1974, Ali won the world heavyweight title again by beating George Foreman. Then he defended a challenge by former heavyweight champion Joe Frazier in a fight Ali called “The Thrilla in Manila.” This was a 15-round fight in the capital city of the Philippines. Ali won that fight.

Ali defended his heavyweight title six more times before he lost to Leon Spinks in February 1978. But Ali came back to beat Spinks and regain the title seven months later.

RETIREMENT

Ali retired in 1981 with a record of 56 wins and 5 losses. He won fame for his graceful footwork, powerful jabs, and confident boasts about his boxing skill. He proclaimed that he was “The Greatest,” and many sports fans agreed.

Ali thrilled fans once again when he lit the flame at the start of the 1996 Summer Olympics in Atlanta, Georgia.

Michael Jordan

Many people think Michael Jordan was the greatest basketball player ever. He led the Chicago Bulls to six National Basketball Association (NBA) championships. He earned the nickname “Air Jordan” because he often seemed to defy gravity on leaps toward the basket. Fans adored his smiling face and his determination to succeed. During his playing career, Michael Jordan became the most famous athlete in the world.

EARLY LIFE

Michael Jordan was born on February 17, 1963, in Brooklyn, New York. His family later moved to Wilmington, North Carolina.

Young Michael’s best sport was baseball. He didn’t make his high school basketball team as a sophomore. Later, he played well enough to be noticed by Coach Dean Smith at the University of North Carolina (UNC). Jordan won a scholarship to UNC.

As a freshman at UNC, Jordan scored the winning basket in the 1982 national college tournament championship game. He played two more seasons at UNC. He also played for the United States team in the 1984 Olympic Games.

In 1984, Jordan entered the NBA player draft. He was chosen by the Chicago Bulls.

NBA LEGEND

Jordan was a star from his first season with the Bulls. He was a scoring machine. The Bulls were not one of the NBA’s better teams, but they gradually improved. They made the NBA playoffs in their first five seasons with Jordan. However, they failed to make the NBA championship finals.

In 1989, Phil Jackson became the Bulls’ head coach. Under Jackson, Jordan became more of a team player, although he remained the NBA’s leading scorer. Jordan developed an incredible “court sense.” He knew where every player was on the basketball court, and what was the best play for the circumstances. In the 1990-1991 season, the Bulls won their first of three straight NBA championships.

In 1993, Jordan retired from basketball. He tried to make it in professional baseball, but he had little success. He rejoined the Bulls in 1995. In the 1995-1996 season, the Bulls started another run of three straight championships.

Jordan retired for a second time in 1998. He became part owner of the NBA’s Washington Wizards. The Wizards were not a good team. Jordan grew frustrated watching them lose. So in 2001, he came out of retirement again and played two seasons with the Wizards.

JORDAN’S RECORD

Jordan retired for good in 2003. He was third on the all-time NBA scoring list, with 32,292 points. He had the highest scoring average in league history: he scored an average of 30.1 points per game during his career. He led the NBA in scoring a record ten times. He won five NBA most valuable player awards. In addition, Jordan created millions of new fans for professional basketball around the world.

Olympic Games

Every four years, athletes from around the world come together to compete in the Olympic Games. Do you know why this event is called the Olympics? The games were first held at Olympia in ancient Greece. The ancient Olympic Games honored the Greek god Zeus. Today, the Olympic Games are held in different cities around the world.

THE ANCIENT GAMES

We know that the ancient Olympics began as far back as 776 bc. That’s when the Greeks began keeping records of the winners. The ancient Games continued until about ad 392, more than 1,000 years!

Athletes came from cities throughout Greece to compete in races, boxing and wrestling matches, gymnastics, and weightlifting. They also threw spears, hurled a discus (bronze disk), and jumped for distance. Wealthy Greeks raced their horses. Winners were crowned with wreaths of olive or palm leaves.

The ancient Olympic Games were not just a sporting event, however. There were competitions in poetry, music, speechmaking, and other arts as well.

At the beginning and end of the Games, animals were sacrificed (killed and offered) to Zeus. A splendid temple was built at Olympia in Zeus’s honor. When people stopped worshiping the Greek gods, the Olympic Games were canceled.

THE MODERN GAMES

The Olympic Games were brought back in 1896. The first modern Olympic Games were held in Athens, the capital of Greece. Only nine countries participated in the first Games, and all the athletes were male.

Today, some 10,000 athletes compete in the Olympic Games, and nearly half of them are female. They represent about 200 nations.

At first, the modern Olympics included only summer sports, such as swimming, rowing, and track and field. Figure skating was added in 1908, and ice hockey in 1920.

The first winter Olympic Games were held in 1924. More winter sports were later added to the Winter Games, including downhill skiing, bobsledding, and ski jumping. Snowboarding and freestyle skiing followed in the 1990s.

From 1924 through 1992, the Winter Games and the Summer Games took place in the same year. After 1992, the next Winter Games were moved up two years, to 1994. Winter Games and Summer Games now occur two years apart. Each of these Games takes place every four years.

GOING FOR THE GOLD

After each Olympic event, medals are awarded to the competitors who finish in first, second, and third place. First-place winners receive a gold medal. Those who finish in second place receive a silver medal, and those in third place, a bronze medal.

Olympic athletes often dazzle the world. In 1912, Jim Thorpe of the United States won the gold medal for two of the most difficult contests in track and field: the pentathlon, which consists of five different events, and the decathlon, which consists of ten events. Thorpe is still the only athlete to have won the pentathlon and decathlon at the same Olympics.

In 1932, Babe Didrikson of the United States became the only Olympic athlete ever to win medals in separate running, jumping, and throwing events. Four years later, African American track star Jesse Owens won four gold medals.

During the 1970s, the thrilling performances of Olga Korbut of the Soviet Union and Nadia Comaneci of Romania inspired a generation of girls to take up gymnastics. Also in the 1970s, American Mark Spitz amazed the world by winning a total of seven gold medals in swimming. In the 1980s and 1990s, Carl Lewis of the United States won a total of nine Olympic gold medals in track-and-field events. Sarah Hughes charmed audiences as she skated her way to a gold medal at the 2002 Winter Olympics. The star of the Summer Olympics in 2004 was American swimmer Michael Phelps, who won a total of eight medals.

Wolfgang Amadeus Mozart

Wolfgang Amadeus Mozart wrote an amazing amount of music, especially for someone who died so young. He was only 35 when he died, yet he composed more than 600 pieces of music. Music lovers place Mozart among the greatest composers who ever lived.

A STAR AS A CHILD

Mozart was born in Salzburg, Austria, in 1756. His father started training him so early that by age six Mozart was performing for the kings and queens of Europe. The young child absorbed the music written at the time on his visits to these royal courts. By eight, Mozart was writing his own symphonies.

People loved Mozart’s lively, often humorous music. Even Austrian composer Joseph Haydn, the dominant figure in music then, was a fan. Mozart was famous, successful, and in great demand. His best-known works include the serenade Eine kleine Nachtmusik, the operas The Marriage of Figaro and The Magic Flute, many outstanding piano concertos, and the Requiem Mass in D Minor.

Mozart often wrote music for people who paid him, but he was happiest working for himself. An archbishop who employed Mozart had little interest in music and once dismissed him with a kick in the rear. Most famously, the Austrian emperor accused Mozart of writing music that was too difficult because it had “too many notes.”

Mozart was always troubled by problems with money. To support his family, he gave music lessons and composed constantly. He was working feverishly when he died at 35 years of age in 1791. The cause of his death is not known, and he was buried as a poor person in an unmarked grave.

MOZART’S GENIUS

Mozart completed more than 600 works in all: 41 symphonies, 27 piano concertos, 23 string quartets, 17 piano sonatas, 7 major operas, and numerous works for voice and other instruments. He had a great gift for creating melodies. Some were charming and amusing. Others were sad and intense. He was able to communicate feelings through his music.

Mozart took the styles of Haydn and others and developed his own style, influencing many composers who came after him. He raised the concerto and string quartet to new levels of brilliance. Mozart is considered one of the world’s great musical geniuses.

Ludwig van Beethoven

Ludwig van Beethoven may sound like a stuffy name. But this German composer was a star in his time, and he had many fans. He broke the rules for writing music. Most people consider Beethoven one of the greatest musicians of all time.

A TROUBLED LIFE

Beethoven was born in Bonn, Germany, in 1770. His childhood was unhappy. His father drank too much. Beethoven’s musical talent was obvious from childhood. He quickly became a talented performer on the piano. In 1792, he moved to Vienna, Austria, to study with Austrian composer Joseph Haydn. Soon Beethoven was playing music that he wrote himself. Many people admired his powerful, dramatic music.

Beethoven was often ill or depressed. He was unable to find a woman who would marry him. Just as he was becoming very successful, he started to lose his hearing. Deafness is the worst fate for a musician. Beethoven’s performing career was over.

Despite Beethoven’s hearing loss, he still wrote music. The music he wrote became even better. His music was richly expressive and revealed feelings such as joy and sadness. He created one bold masterpiece after another. Besides piano music, Beethoven wrote string quartets (pieces for four stringed instruments) and other kinds of chamber music. Chamber music is written for small groups, and people can play it in their homes or in small halls. Beethoven also wrote songs, two masses, an opera, and nine outstanding symphonies.

Crowds loved him and adored his music. Beethoven was famous, although not happy. In 1827, he got pneumonia and died in Vienna.

WHAT MAKES BEETHOVEN’S MUSIC SPECIAL?

Beethoven studied works by Haydn, German composer Johann Sebastian Bach, and Austrian composer Wolfgang Amadeus Mozart. Then he broke their rules and made music that was like no one else’s. It was emotional and challenging. Beethoven wanted his music to express ideas as well as emotions. He wanted it to praise freedom and equality and other high ideals.

Some of Beethoven’s well-known achievements are the Moonlight Sonata for piano, the Fifth Symphony, and the Ninth Symphony. The Fifth Symphony has a famous four-note opening, da-da-da-dum. The Ninth Symphony ends with a triumphant chorus called “Ode to Joy.” Beethoven’s music set a standard that later composers measured their work by.

Leonardo da Vinci

Leonardo da Vinci excelled as a painter, sculptor, architect, engineer, and scientist. He had endless curiosity. Leonardo wanted to understand how things worked. He wanted to put down on paper what he saw. He left thousands of pages of drawings and notes that recorded his thoughts.

GOOD AT EVERYTHING

Leonardo was born in 1452 in the small town of Vinci, near Florence, Italy. He had little schooling and was largely self-taught.

Leonardo seemed to be good at everything he tried. He was handsome, a good speaker, and a fine musician. He trained as a painter with Andrea del Verrocchio, a leading artist in Florence. Leonardo later worked for dukes and kings.

HIS MOST FAMOUS PAINTINGS

Leonardo produced a relatively small number of paintings, and he left some of them unfinished. But he had original ideas that influenced Italian artists long after his death. Leonardo believed painting was a science. He applied scientific thinking in his art so that his paintings looked more like the real world. One of his most important painting techniques was sfumato, a blending of one area of color into another so there are no sharp outlines.

Leonardo used sfumato in one of his most famous paintings, the Mona Lisa. When you look at this portrait, notice how colors shade into each other on her face and hands. See how Leonardo has blurred the edges of her mouth to give her the hint of a smile. This mysterious smile has fascinated people for centuries. It looks as if Mona Lisa’s expression might change at any moment because of the way Leonardo has softened the edges of the mouth, eyes, and cheeks. She seems almost alive.

Many people consider a mural by Leonardo known as The Last Supper to be his masterpiece. Christ, seated in the middle of The Last Supper, has just announced that one of his 12 apostles will betray him. Leonardo places the figures in this painting in a way that increases the drama of the announcement. Christ is the calm center. His body, which is set slightly apart from the others, forms a stable triangle. The apostles are arranged in four groups, some leaning toward Christ and some leaning away. Their gestures and the expressions on their faces reveal their reactions to Christ’s words.

HIS DRAWINGS AND NOTEBOOKS

Drawing was Leonardo’s favorite tool. He said that drawing was a better way of communicating ideas than words were. He drew catapults and war machines. He drew the muscles and skeletons of human beings and other animals. He drew clouds, swirling water, and storms. He designed churches that were never built.

Leonardo’s drawings and theories are contained in numerous notebooks. His ideas were far in advance of what other people were thinking at the time. But the notebooks were not published during his lifetime. Had his notebooks been published, they might have revolutionized scientific thinking in the 1500s. Leonardo’s deep love of research was the key to both his artistic and scientific endeavors. Leonardo died in 1519.

Elvis Presley

Was Elvis more famous for his music or his hips? True, his rock-and-roll style was fresh and daring. But so was the way he swiveled his hips when he sang.

Presley was the first singer to blend the rhythm-and-blues style of black musicians with the country-and-western style of white singers. In doing so, he became a pioneer of the rock style. Most major rock singers claimed that Presley influenced them.

HIS FIRST HITS

Elvis Aaron Presley was born in Tupelo, Mississippi, in 1935. He grew up listening to gospel music, country and western, and rhythm and blues. At age 10, he won a talent contest singing a ballad called “Old Shep.” In his teens, he taught himself to play the guitar.

After high school, Elvis worked as a truck driver. In 1953, he decided to record some songs for his mom’s birthday. The studio he went to was thrilled to release Elvis’s first two records, “That’s All Right Mama” and “Blue Moon of Kentucky.”

Elvis was a star overnight. Five of his records shot to number one in sales: “Heartbreak Hotel,” “I Want You, I Need You, I Love You,” “Don’t Be Cruel,” “Hound Dog,” and “Love Me Tender.” His rebellious music was matched by his electric performance onstage. He had a way of moving his body that drove teens into a frenzy (and made parents frown).

MOVIE STAR

Elvis began starring in movies that featured his own music: Love Me Tender (1956), Jailhouse Rock (1957), and King Creole (1958). He served in the United States Army from 1958 to 1960. After the Army, he went back to musical films. Critics disliked his later movies in which his rebellious image became more wholesome.

His hit songs continued, though, with “It’s Now or Never,” “Return to Sender,” and “In the Ghetto.” Fans worshiped him. They were crushed when he died, in 1977, probably as a result of overusing prescription drugs. You can visit his grave at his mansion, Graceland. It’s a major tourist site in Memphis, Tennessee.

Michelangelo

Michelangelo was an artist of extraordinary ability. He is known primarily as an outstanding painter and sculptor, but he was also an accomplished architect and poet. He had a forceful personality as well.

HE LOVED A CHALLENGE

Michelangelo Buonarroti was born in Caprese, a village in Italy, in 1475. He grew up in Florence, the artistic center of Europe during the 1400s. At 13, he began to train as a painter.

Michelangelo believed that the nude (naked) male figure was the most important subject in art, and he loved a challenge. He preferred to create art that required hard work. For example, he carved blocks of marble that other sculptors had rejected, and he created enormous paintings on very high ceilings. In painting, he chose to put his figures in poses that were especially difficult to draw. In carving, he cut away the stone in a way that seemed to release a human figure trapped inside.

HIS BEST WORK

Michelangelo’s early sculptures made him famous. His Pietà shows the dead Christ lying in his mother’s lap. Michelangelo emphasizes Christ’s suffering through the limp, frail body that is cradled by the Virgin Mary. Michelangelo carved a huge statue of the biblical hero David. It shows the strong, young David calmly holding the slingshot he is about to use to slay the giant warrior Goliath. The city of Florence displayed the statue of David as a symbol of its political strength.

Michelangelo’s greatest challenge was to paint the gigantic ceiling of the Sistine Chapel in Rome. To paint the Sistine Ceiling, he had to lie on his back on a wooden platform high in the air. It took him nearly four years, but Michelangelo created some of the most memorable images of all time. The Sistine Ceiling tells the biblical story of the Book of Genesis. It begins with the creation of the world and finishes with the story of Noah. It contains almost 350 painted human figures, all of them larger than life-size.

Later, Michelangelo painted the Last Judgment in the Sistine Chapel, on a wall above the altar. This mural is filled with swirling nude bodies. Some rise from the grave to heaven. Others descend in agony to hell. Michelangelo’s greatest architectural work was a design for the dome of Saint Peter’s Cathedral in Rome.

Michelangelo died in 1564. He had an enormous influence on European artists of his time and on those who came after him. After Michelangelo, artists competed with each other in painting the human body in difficult poses.

Human Body

Your body is amazing. Did you know you have more than 200 bones and 600 muscles? Your nerves carry messages from your brain to make those muscles cooperate so you can stand up and move around. Your blood vessels could stretch all the way around the planet! White blood cells stand guard like soldiers waiting to attack any invader. Your heart, lungs, stomach, and other organs are at work 24 hours a day for your entire life. There are too many parts inside you to count, but they all work together to keep you alive. No machine is as complex as you are.

The many parts of your body are grouped into systems. Each system has a job to do in your body. The systems work together to keep you alive and healthy.

BONES AND MUSCLES

The bones and muscles of your body let you move around. Tough bands called ligaments connect your bones to each other. The connections are called joints. Some joints can move a lot. Your arm at your shoulder joint can move in circles. Your lower leg at your knee joint can only move back and forth. The bones in your skull have special joints that cannot move at all.

Muscles attached to bones pull on them to make your body move. The muscles get their orders to move from your brain and nerves.

THE NERVOUS SYSTEM

Your brain and nerves make up your nervous system. Your brain is the command center of your body. Your brain sends signals through your nerves. Some signals from your brain control your muscles. Suppose you want to walk across the street. Your brain sends signals that tell the muscles in your legs to move.

You do not have to think about some of the signals your brain sends out through your nerves. Your nervous system tells your heart to beat and your lungs to breathe even when you are sleeping.

Nerves also send signals back to your brain. Nerves tell your brain what your eyes see. They tell your brain when you stub your toe.

CIRCULATORY SYSTEM

Your circulatory system is made up of your heart and blood vessels. Blood vessels are flexible, hollow tubes. Your heart pumps blood through blood vessels. It sends blood to your lungs to pick up oxygen. It pumps blood out to all parts of your body.

Arteries are blood vessels that carry oxygen-rich blood out to your body. Veins are blood vessels that carry blood back to your heart. The blood vessels near your heart are thick. Farther from your heart, the blood vessels are smaller.

The tiniest blood vessels are called capillaries. Capillaries go all through your body. They give up oxygen and nutrients that your body needs. They carry away waste products.

IMMUNE SYSTEM

Your immune system defends against germs and other things that make you sick. White blood cells and other chemical weapons of the immune system rush to find and destroy the germ. Special white blood cells and chemical “watchdogs” called antibodies stand guard. Sometimes antibodies grab onto a germ that shows up. White blood cells called T cells attack germs directly.

Many T cells get stored in little pouches called lymph nodes. Lymph nodes in your neck and other places sometimes swell up when your body is fighting off germs. Some people call this “swollen glands.”

RESPIRATORY SYSTEM

Respiration is breathing. You use your lungs to breathe. You breathe air into your lungs. The air contains oxygen, a gas you need in order to live. Blood in your lungs picks up the oxygen and carries it to all parts of your body.

Blood coming back to your lungs gives off carbon dioxide, a waste gas. Your lungs send carbon dioxide out of your body when you breathe out.

DIGESTIVE SYSTEM

Your digestive system is like a long tube that goes down through your body. Your digestive system breaks down the food you eat. It breaks down food so that your body can use it for energy.

Your teeth grind up food in your mouth and mix it with saliva. You swallow the ground-up food. It goes into your stomach where it gets broken down even more.

Food goes from your stomach to your small intestine. Nutrients pass through the walls of your intestine and into your blood. Your blood carries the nutrients to all parts of your body.

Your body gets rid of any leftover waste products. Liquid waste products go to your kidneys. You get rid of these waste products as urine. Solid waste products go to your large intestine. You get rid of these waste products as feces.

OTHER SYSTEMS

Your body has other systems. One is the reproductive system, which differs in males and females. The male reproductive system makes sperm. The female reproductive system makes eggs. An egg fertilized by sperm grows into a baby.

The endocrine system is made up of glands. The pituitary gland under the brain is the master gland of the body. It controls the activities of other glands. Glands control how your body burns food for energy. They control how fast you grow and do many other important things in the body.

Sleep and Dreaming

Dogs sleep, cats sleep, and you sleep. All mammals and birds sleep. Scientists are not sure if fish, reptiles, and insects sleep.

Big animals sleep less, and small animals sleep more. Elephants and giraffes sleep only 2 to 4 hours a day. Bats, opossums, and armadillos sleep 18 hours a day or more!

Even kids need more sleep than grownups. A newborn baby sleeps 17 to 18 hours a day. A 10-year-old needs about 10 hours of sleep a night. Grownups need between six and nine hours of sleep a night. Some people need more sleep than others.

WHY DO WE HAVE TO SLEEP?

Scientists do not know for sure why you sleep. They do have some ideas.

Safety could be one reason for sleep. People and other animals might sleep because it keeps them safe at night. It’s hard to see in the dark. Enemies could sneak up and attack animals that are wandering in the darkness. Most mammals and birds go to trees, underground dens, or nests at night. Prehistoric people went into caves or other shelters. They covered up with furs and fell asleep. You go into your home at night and snuggle up in bed.

Sleep might also help your body work better. Things go wrong if you do not get enough sleep. It is hard to think and work and play unless you get plenty of sleep.

WHAT HAPPENS WHEN WE FALL ASLEEP?

Scientists have learned a lot about what happens when you lie down, close your eyes, and fall asleep. They study people in sleep labs.

Sometimes your eyeballs move back and forth while you’re asleep. They move fast. Scientists call this kind of sleep REM sleep. REM stands for rapid eye movement. Your body may twitch during REM sleep. Your brain is also very busy during REM sleep. It is almost as busy as when you are awake. What do you think your brain is doing? Here’s a clue: You dream during REM sleep.

There is another kind of sleep. Your eyeballs do not move. Scientists call this NREM sleep. NREM stands for nonrapid eye movement. Your brain is not very busy during NREM sleep. You go back and forth between REM and NREM sleep all night long.

WHY DO WE DREAM?

Scientists have done many studies on dreams. They think your senses may have a lot to do with dreams. In dreams, you see and hear things. Dreaming is not like thinking about things.

You have feelings during dreams. You may feel happy or angry. You feel fear if you have a nightmare.

Your memories may have something to do with your dreams. Dreams are often like stories that stop before they are finished.

DO DREAMS MEAN ANYTHING?

People in ancient times looked for meaning in dreams. The ancient Egyptians believed dreams could tell the future. Some psychologists think that dreams show what people feel deep inside. They ask people to talk about their dreams.

Some scientists think that dreams have no meaning. They think that dreams just come from nerve signals in your brain. Other scientists think that dreams are important for memory. They may help your brain sort out what to remember and what to forget.

Memory

Is memory important to you? How often do you think you use yours? Actually, you use it every moment of every day. You remember who you are, where you live, and what you are doing. Without memory, you could not survive!

There are three kinds of memory: sense memory, working memory, and long-term memory. Think of them as three connected rooms in which you store different kinds of memories.

SENSE MEMORY

The first kind of memory is sense memory. Everything you are sensing right now is stored here. Perhaps you feel the Sun on your face or smell the aroma of food.

Sense memories last only a few seconds, but they connect one moment to the next. They give your life a flow, even though they are quickly forgotten.

WORKING MEMORY

You keep a few items in working memory. These are memories you need for what you are doing. Suppose you look up a friend’s telephone number in the phone book. You’ll probably remember the number for a little while. But if you get distracted, you might quickly forget it.

A memory usually stays in your working memory for just a few days at most. Working memory has another limit, too. Only a small number of items fit into it at any given time.

LONG-TERM MEMORY

Memories you want to keep for a long time go into your long-term memory. They can stay with you all your life. In long-term memory, you can store a huge number of items.

Can you remember how to play your favorite game? Do you recall your first birthday party? If so, you are bringing up memories that are stored in your long-term memory.

Sometimes, people have trouble finding a particular long-term memory. Have you ever struggled to remember a familiar name or fact? When this happens, people sometimes say the information is on “the tip of the tongue.”

IMPROVING MEMORY

Learning and remembering are connected. The trick to remembering something is learning it well in the first place. That way, you can store what you’ve learned in your long-term memory.

One way to improve your memory of something is by using a mnemonic (neh-MON-ick) device. A mnemonic device puts information into a form that’s easy to remember. For example, students sometimes memorize the Great Lakes with the word homes. It stands for Lakes Huron, Ontario, Michigan, Erie, and Superior.

Brain and Nervous System

What kind of supercomputer can write stories, do math problems, draw pictures, play games, see through eyes, hear someone talking, talk back, and network with devices that make snacks in the microwave oven? Your brain and nervous system can do all these things. Do you think a computer will ever be as powerful as your brain?

You think with your brain. Your brain also sends signals through a network called your nervous system. It tells your legs to walk and run. It tells your hands and arms to put popcorn in the microwave. You don’t even have to think about many of the things your brain does. Your brain tells your heart to beat. It tells your lungs to breathe in and out, even when you are sleeping.

Your brain also controls your feelings. Such feelings as joy, sadness, love, anger, and fear all come from your brain.

WHAT IS MY BRAIN MADE OF?

Your brain is made of about 100 billion nerve cells. It looks like a lump of pinkish-gray jelly. The surface of the brain is wrinkled, and deep grooves divide it into sections. A network of blood vessels brings oxygen and food to your brain cells and carries away wastes. Your brain is protected by bone called your skull. Liquid and skinlike tissues also protect your brain.

When you were born, your brain weighed about • pounds (about 0.35 kilograms). Your brain keeps on growing while you grow up. By the time you reach the age of 20, your brain will weigh about 3 pounds (1.3 kilograms).

Your brain has three main parts. The parts are called the cerebrum, the cerebellum, and the brain stem. The cerebrum makes up the largest part of the brain. The cerebellum is underneath the back part of the cerebrum. The brain stem connects with the spinal cord at the bottom of the brain.

Your cerebrum and cerebellum are divided into two parts. These parts are called the right brain and the left brain. The right side of your brain controls the left side of your body. The left side of your brain controls the right side of your body. Nerves from the right and left side of your body cross over when they enter your brain.

WHAT DOES THE CEREBRUM DO?

Your cerebrum makes up most of your brain. Your cerebrum solves problems and makes wishes. All of your thinking goes on in your cerebrum. Speech, language, and emotions come from your cerebrum, especially your cerebral cortex. The cerebral cortex is the outer part of the cerebrum.

Your cerebrum also gets signals from your senses. Nerves carry the signals. Nerves from your eyes and ears go to parts of the cerebrum that let you see and hear. Nerves carry signals to your cerebrum that let you feel, smell, and taste.

Your cerebrum sends messages out along nerves. The messages tell your legs to walk or run. They tell your arm and hand to wave when you see a friend across the street.

WHAT DOES THE CEREBELLUM DO?

Your cerebellum coordinates and fine-tunes your body movements. Your cerebrum might tell your hands and arms to hit a baseball. Your cerebellum controls how you swing the bat and make contact with the ball.

Your cerebellum helps your fingers play the piano, guitar, or violin. It helps you keep your balance when you run, jump rope, or walk along a curb.

WHAT DOES THE BRAIN STEM DO?

Your brain stem takes care of all the things that you do but don’t need to think about doing. It keeps your heart pumping blood. It keeps your lungs breathing air. It makes your eyes blink. It pulls your hand back really fast if you touch a hot pot on the stove.

WHAT IS THE NERVOUS SYSTEM?

Your nervous system consists of the brain, spinal cord, and nerves that run throughout your body. The nervous system carries messages to your muscles and organs. These messages tell your body what to do.

Your spinal cord is made of bundles of nerves. It starts in your neck and goes down your back. Nerves go out from the spinal cord to other parts of your body. Nerves from the spinal cord extend to the tips of your fingers and toes. Your spine, or backbone, protects your spinal cord.

Colds and Flu

You start sneezing. Your throat gets sore and scratchy. You have to blow your nose a lot. You don’t feel very well. Do you have cold? Or do you have the flu?

Colds and flu are illnesses caused by germs. They are both caused by germs called viruses. But they are caused by different kinds of viruses. Colds are often called common colds. Flu is short for influenza.

IS IT A COLD OR THE FLU?

Signs that you have a cold or the flu are called symptoms. The symptoms of a cold and the symptoms of the flu are slightly different.

The symptoms of a cold are sore throat, cough, sneezing, and a stuffy, runny nose. Colds usually do not cause a fever.

Flu symptoms are like cold symptoms, but the flu also causes chills, fever, and headaches. It makes you feel tired and achy all over.

A cold or the flu usually lasts about a week. Every once in a while they can lead to a more serious sickness, such as an ear infection or a lung infection called pneumonia.

CATCHING A COLD OR THE FLU

People once thought you could catch a cold from getting a chill in cold weather. They thought that wet feet or drafts of cold air could give you a cold.

We now know that germs cause colds and flu. The germs are passed from one person to another. They travel in coughs and sneezes.

More colds and cases of flu happen in cold weather because people spend more time together indoors when it’s cold outside. It is easier for germs to spread when people are close together.

IS THERE A CURE?

There is no cure for the common cold. People take medicine to help their sore throats, coughs, and runny noses. Doctors say that resting in bed is the best way to treat a cold.

There is no cure for the flu, either. Doctors can give medicine to make you feel better. Resting in bed and drinking lots of juice and water is the best way to treat the flu.

AVOIDING A COLD OR THE FLU

You can get a flu shot to help keep you from catching the flu. A flu shot, or vaccination, helps your body fight off flu germs if they attack. But it doesn’t always work. The flu virus keeps changing. When it changes, the old vaccine no longer works. Doctors have to keep making new vaccines. For this reason, you need a new flu shot every year. Sometimes the flu changes enough in a single year that you can still catch it even if you’ve been vaccinated.

There is no vaccine against the common cold because more than 100 different kinds of viruses cause colds. These viruses also keep changing.

One thing you can do to protect against cold and flu germs is wash your hands before you eat anything or touch your face. Your hands may pick up the germs from door knobs or other things touched by someone with a cold. Washing your hands thoroughly kills the germs.

You can also try not to spread germs when you have a cold or the flu. Use tissues when you sneeze. Cover your mouth when you cough. And wash your hands frequently to keep from spreading cold germs to others.

Skin

Your skin is your body’s largest organ, larger than your heart or lungs or brain. Skin covers your whole body, from the top of your head to the soles of your feet. You could not live without your skin. Skin keeps germs and other harmful things out of your body. It keeps water, blood, and other fluids that you need inside your body.

You are always losing your skin and growing new skin. The outside layer of your skin is dead. It flakes off all the time. New skin grows to replace it.

LAYERS OF SKIN

Your skin has an outside layer called the epidermis. Under that is a layer called the dermis. Under those two layers is a layer of fat.

The epidermis protects the layers beneath it from minor scrapes, jabs, and sunburn. The bottom of your epidermis is always making new skin cells. The dead cells on the top of your skin are constantly dropping off.

The dermis is full of nerves and blood vessels. The nerves send signals to your brain when you touch something. The dermis gives your skin its toughness and strength. It also helps keep your body cool in hot weather and warm in cold weather. A scrape only bleeds if it’s deep enough to go through the epidermis and into the dermis.

There is a layer of fat under the dermis. This layer is thicker than both top layers of skin.

WHAT GIVES SKIN ITS COLOR?

The top layer of skin has a chemical called melanin. Melanin gives your skin its color. The more melanin you have, the darker your skin is. Patches of skin with extra melanin make freckles.

Melanin protects your skin from the Sun’s harmful rays. Your skin makes more melanin when you are out in the Sun. More melanin gives you a tan.

Melanin has its limits. Too much sunlight is bad for your skin. Harmful rays from the Sun can burn your skin. They can cause skin cancer.

WHAT IS HAIR MADE OF?

Hair is made of skin cells. A hair grows from a root under the skin. The hair grows up inside a shaft through the layers of skin. The part of the hair that you see is made of dead cells.

The color of hair, like the color of skin, comes from melanin. Melanin is made in the hair root. The hair of older people turns gray because the root stops making melanin.

The shape of the hair shaft gives you straight or curly hair. A round shaft makes straight hair. An oval-shaped shaft makes wavy hair. A comma-shaped shaft makes curly hair.

WHAT ARE FINGERNAILS MADE OF?

Fingernails and toenails are also made of skin cells. These nail cells are very hard. Nail cells start growing inside your fingers and toes. The cells die. New cells push the dead cells outward. This makes nails on your fingers and toes grow.

WHAT CAUSES PIMPLES?

Plugged pores cause pimples (zits). Pores are openings in the skin. Dead skin cells can plug up a pore. The plug can make a blackhead or a whitehead on top of the skin.

Pores allow oil to get to the surface of your skin. This oil is the kind that gives you oily skin, not the kind that gets made into gasoline. The oil keeps your skin and hair from drying out. Groups of cells called glands make the oil. Oil glands are almost everywhere in your body. There are many oil glands on your face and scalp.

The oil cannot get out of a plugged pore. Soon a pimple or a red lump forms. The red lumps can leave scars. Squeezing a pimple can cause a scar.

Doctors can help teenagers with lots of pimples. Doctors can give them medicine that will help make the pimples go away.

WHAT MAKES A SCAB?

Have you ever scraped your knee or cut your finger? Scabs grow over scrapes, cuts, and other wounds that bleed. The blood dries and hardens. The blood turns into a scab.

New cells grow under the scab. The cells join up and cover the cut. When the skin is healed, the scab drops off.

Smoking

Smoking is “hateful to the nose, harmful to the brain, and dangerous to the lungs.” This was the view of England’s king James I in 1604. For long afterward, smoking was considered harmless. Today, more and more people agree with King James.

TOBACCO AND NICOTINE

Smoking means breathing the smoke of burning tobacco leaves. Tobacco is a plant.

Tobacco is processed for smoking in different ways. People smoke tobacco in pipes, cigars, and cigarettes.

Tobacco smoke contains about 4,000 chemicals. One of them is nicotine. In large amounts, nicotine is a poison. In small amounts in the human body, nicotine stimulates the nerves. It makes the heart beat faster.

Nicotine is highly addictive. This means that smokers become dependent on its effect as a stimulant. When this effect wears off, the body strongly desires more. That is why people who smoke find it hard to stop.

HISTORY

Native Americans smoked tobacco as long as 2,000 years ago. Explorer Christopher Columbus saw them smoking in 1492. His crew brought tobacco to Europe. European sailors spread it around the world. Some people believed then that smoking could cure diseases. By 1600, people smoked mainly for enjoyment.

Cigarettes were invented in Europe. They did not become popular until the 1800s. They were expensive because people had to make them by hand. Then a cigarette-rolling machine was invented.

In the 1940s, doctors began to notice connections between smoking and lung cancer and other diseases. They began to study the chemicals in cigarette smoke. Many of these chemicals were found to cause cancer. A group of scientists prepared a report for the United States government in 1964. The report declared cigarette smoking to be a serious health danger.

Since then, smoking in the United States has greatly declined. Health warnings appear on cigarette packages. Smoking is banned on most airline flights. It is banned from many offices and public places.

SMOKING AND HEALTH

Cancer experts say that cigarettes kill hundreds of thousands of Americans every year. Lung cancer kills more Americans than any other kind of cancer. Smokers are 20 times more likely than nonsmokers to develop lung cancer.

Smokers also are at greater risk for other forms of cancer and other lung diseases. Mothers who smoke can injure the health of their babies.

Quitting smoking greatly lowers the chances of dying from diseases caused by smoking.

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