butterfly cycle

8/8/2019 Butterfly Cycle

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Butterfly cycle

A butterfly starts its life as an egg, laid by a female adult butterfly after mating. Butterfly eggs vary in size and shape, but

most are surrounded by a protective hard shell.

A caterpillar develops within the egg and then eats its way out of the shell.

A caterpillar spends all its time eating. As it grows, the caterpillar becomes too large for its skin and molts (sheds its skin)

to reveal new skin. Depending upon the type of butterfly, caterpillars molt four or five times.

When the caterpillar reaches its final size it stops feeding. The caterpillar wriggles and twists to gradually remove its old

skin, revealing a new protective skin called the chrysalis.

Inside the chrysalis, the caterpillar changes from a wormlike creature into an adult butterfly.

When the butterfly reaches adulthood, it leaves the chrysalis. It pumps blood into its crumpled wings and expands them

to their full size before flying away.

Frog Life Cycle

A frogs life is divided into two main stages. In the first stage, a tadpole hatches from eggs. The tadpole breathes

underwater through gills and swims like a fish. In the second stage, the tadpoles body changes shape. It becomes an

adult frog that has legs for jumping on land and lungs for breathing.

They may be cuddly, playful, and fun. They can delight us with their grace and beauty. Theyre part of our families.

Sometimes, theyre our best friends. Its easy to see why people love their pets!

THE MOST POPULAR PETS

More than half of the homes in the United States have a pet. Cats and dogs are the most popular pets. One out of three

households has a cat or dog. The most popular purebred dog is the Labrador retriever. However, cats outnumber dogs in

American homes.

Birds rank next in popularity, but theyre far behind cats and dogs. The most popular pet bird is the parakeet. Many

people keep small animals like rabbits, hamsters, and gerbils as pets. Fish also are popular. Turtles are the reptiles most

often kept as pets.

PETS NEED LOVE AND CARE


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We expect our pets to love us. Its important that we give them the love and care they need in return. Dogs especially

want close contact with their owners. Our pets depend on us for food, grooming, attention, affection, and medical care.

Before you get a pet, its important to know what its needs are.

A pet is a responsibility as well as a companion. Keeping a pet means keeping a promise to love and care for it. If you can

do that, you can have wonderful experiences with pets.

CHOOSING A PET

Dogs generally offer total and unquestioning love. Most dogs are loyal friends and great playmates. Dogs also require a

lot of attention. They need to be walked and played with. They need to be housebroken and trained to obey. Different

breeds of dogs have different personalities and requirements, so dont choose a dog just by its looks!

Many people who dont have enough time to give a dog the attention it needs choose a cat instead. Cats can live

indoors, and they dont need training. Cats like to play, and they make affectionate companions. Theyre endlessly

curious, and they entertain us with their pranks.

Pets in cages may be best for people without a lot of time or space. Rabbits, hamsters, and gerbils are active, friendly,

and easy to care for. Parakeets enjoy talking and playing with mirrors and toys. They learn to perch on your finger.

Watching fish in a home aquarium is also relaxing and fun. Tropical fish can be very beautiful.

PRACTICAL PETS

Pets are fun, but they also do work. Animals can be useful to have around. Thats why wild animals got tamed as pets.

Dogs, especially, can do lots of things. They can stand guard in the night. Hunters use dogs for fetching. Ranchers use

them to help herd sheep or cattle. The police use dogs to sniff for bombs. Some dogs are trained to help blind people

and deaf people.

Cats catch mice. The ancient Egyptians worshiped cats for keeping their fields free of pests. Pets can even be actors!

Trained dogs sometimes appear in movies or television shows.

Having a pet can be good for your health. Pets offer companionship and make people feel less lonely. Petting an animal

also helps people relax.

PROBLEMS WITH PETS

Pets can cause problems, too. Dogs dig in the garden. They chew up household objects and can even bite people. Cats

like to scratch furniture. Both cats and dogs can make a mess on the rug. Some people have allergies to animals.

But the biggest problem is that there are more pets than there are homes for them. Cats and dogs give birth to more

cats and dogs. The number of unwanted pets is enormous. Thats why its important to consider having your pet

neutered or spayed. Otherwise, you could wind up with lots of extra animals.

Microsoft Encarta 2009. 1993-2008 Microsoft Corporation. All rights reserved.

A tuber is a food-storing stem of a plant that grows underground. The tasty part of a potato plant, pictured here, is a

tuber. Other types of tubers include yams and water chestnuts.

Roots grow underground, where they collect and store water and nutrients. The roots of many plants are fleshy and

good to eat. A carrot is actually the root of the carrot plant, shown here. Other plants with edible roots include sweet

potatoes, beets, turnips, and parsnips.


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Legumes are plants that grow protein-rich seeds in protective cases called pods. Soybeans, shown here, peas, peanuts,

lentils, and beans are all types of legumes.

Many plants grow tasty leaves. The thick, rounded leaves of cabbage, pictured here, have a mild, salty taste. Other leafy

plants that are good to eat include cauliflower, broccoli, celery, and brussels sprouts.

Cereals are plants in the grass family that are grown for their seeds, known as grain. The grain of the oat plant, shown

here, is used in breakfast cereals and as an ingredient in peanut butter, margarine, and chocolate. Other types of cereals

include wheat, barley, rice, and corn.

How Plants Make Food

Plants make their own food in a process called photosynthesis. Photosynthesis takes place inside plant cells called

chloroplasts. Chloroplasts change sunlight, water, and carbon dioxide (a gas in the air) into sugars, a type of food used

by the plant to grow. Photosynthesis also makes oxygen, which is released into the air. Microsoft Corporation. All Rights Reserved.


How Plants Make Food

Plants make their own food in a process called photosynthesis. Photosynthesis takes place inside plant cells called

chloroplasts. Chloroplasts change sunlight, water, and carbon dioxide (a gas in the air) into sugars, a type of food used

by the plant to grow. Photosynthesis also makes oxygen, which is released into the air.



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Parts of a Fruit

Fruit is the part of a flowering plant that carries the seeds. Most fruit, including the cherry pictured here, has a fleshy

fruit wall that protects the seed inside. It's this fleshy part that makes fruit so good to eat.

They grow on mountains and in deserts. They grow in freshwater lakes and streams. They grow in the heat of the tropics

and in places covered with snow. They even grow in the salt water of the ocean. What are they? Plants, of course!

WHAT IS A PLANT?

Plants are one of the five main groups of living things. These groups are called kingdoms. The plant kingdom includes

such living things as grasses, trees, ferns, bushes, and flowers. Botanists, the scientists who study plants, have counted

more than 260,000 species (kinds) of plants.

Plants vary greatly in size and shape. Some plants are so small they can hardly be seen. Other plants tower above the

land. The giant sequoia trees of California are one of the largest living things on Earth. They can grow to heights of nearly

300 feet (90 meters)!

Just like animals, plants are made up of tiny structures called cells. But unlike animal cells, plant cells are surrounded by

a stiff material called cellulose. Most animals move around and eat other things. Plants are different. Plants that grow on

land usually stay in one place and make their own food.

Most plants are green because they have a green chemical called chlorophyll. Plants are different from mushrooms and

other fungi. Fungi do not have chlorophyll.

WHAT ARE THE MAIN KINDS OF PLANTS?

Almost all the members of the plant kingdom are seed plants. They grow from seeds. Most seed plants are flowering

plants, or angiosperms.

But there are some groups of plants that do not grow from seeds. Botanists call these groups bryophytes, ferns,

lycophytes, and horsetails.

WHAT ARE FLOWERING PLANTS?


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People who plant flower gardens fill them with flowering plants. Oaks, maples, and other trees that turn bright colors in

autumn are flowering plants. The grasses on lawns are flowering plants. Almost all the fruits and vegetables you eat

come from flowering plants.

Flowering plants make seeds that are inside a covering.Angiosperm, the name for flowering plants, means enclosed

seed.

You probably have seen many seeds of angiosperms. The seeds are inside fruit. Bite into an apple, a peach, or a pear and

you will find one or more seeds. The seeds started to grow inside the beautiful blossoms that covered these fruit trees inthe spring.

WHAT ARE OTHER SEED PLANTS?

Unlike flowering plants, some seed plants make seeds that are not inside a covering. They are called gymnosperms, a

word that means naked seed.

The best-known kinds of gymnosperms are conifers. Conifers are evergreens. They stay green all year long. Arborvitae,

cedar, cypress, fir, hemlock, juniper, pine, and spruce trees are all conifers.

Conifers and other gymnosperms do not have flowers. Conifers do have leaves, but they are usually thin like needles.The seeds of conifers are in cones.

WHAT ARE THE MAIN PARTS OF PLANTS?

Most plants have three main parts: roots, stems, and leaves. The roots are in the ground. They hold the plant in the soil.

Roots take up water and minerals the plant needs.

Stems usually are above ground. They carry food and water. The stems of some plants, such as dandelions, are thin and

delicate. Trees have thick, strong stems. The stems are trunks covered with bark.

Leaves come out of the stems of plants. Green plants use light, water, minerals, and carbon dioxide (a gas in the air) to

make food in their leaves.

Leaves have many different shapes. Some are sharp spines that protect the plant from animals. Some leaves are brightly

colored. Flowers are a kind of leaf.

HOW DO PLANTS GROW?

Most plants grow from seeds. Seeds need soil, water, and light to grow. A bean is a seed. You can make a bean plant

grow. Heres how.

Put a bean in a paper cup filled with soil. Set the cup near a window where there is plenty of sunlight. Water the bean

often. A root will grow downward from the bean. A green shoot will start to grow upward from the bean. Soon you will

see leaves start to grow out of the shoot, or stem.

Wind and water may carry some seeds far from the plants that made them. Sometimes seeds are planted by animals

that eat fruit. Apples, peaches, and cherries are examples of seed-bearing fruits that animals like to eat.

Cherries, for instance, are a favorite food of birds. After a bird has eaten the fruit, it may fly off and drop the cherry

stone, or seed, far away. This seed may start to grow and make a new cherry tree.

WHERE DO SEEDS COME FROM?


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Many kinds of plants have male and female parts. These plants reproduce, or make seeds, sexually. In flowering plants,

the male and female parts are in the flowers. In pine trees and other conifers, the male and female parts are in the

cones. Conifers have male and female cones.

The male part of a flower is called the stamen. It gives off a powdery substance called pollen. The female part is called

the pistil. An egg forms in the pistil. Pollination occurs when some of the pollen gets to the pistil. A pollen grain joins

with an egg. When this happens, a seed begins to grow.

In some species, the pollen and egg can come from the same plant. In other species, they must come from differentplants. But how does pollen move? Insects, wind, and water can all help move the pollen.

Have you seen bees or butterflies around flowers? Bees and butterflies like to drink nectar from the flowers. As they

enjoy their tasty treat, some of the pollen sticks to their bodies. They carry it with them to other flowers, leading to

pollination.


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. Earths axis is an imaginary line that goes through Earth from the North Pole to the

South Pole. Earths 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. Earths path around the Sun is slightly oval-shaped. This oval shape causes Earths 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. Earths 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 Earths 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.


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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 Earths

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 Earths 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 Earths 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 Earths core. The core i s mostly

iron. The outer part of the core is l iquid metal. The inside of the core is solid metal. Scientists believe that the liquid

metal makes Earth a giant magnet and creates Earths magnetic field.

Earths 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.


Have you ever played the cloud game? You lie on the grass and look up at the clouds. You try to see different shapes in

the clouds. One cloud might look like the head of a horse. Another might look like a car. You watch as the clouds move

across the sky. You watch the clouds change shape as they move.


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WHAT ARE CLOUDS MADE OF?

Clouds are made of small drops of water or tiny pieces of ice. The water and ice in clouds come from Earths surface,

especially from lakes, rivers, and oceans. Water on the surface evaporates. It changes into a gas called water vapor.

Water vapor goes up into the air.

The higher up you go, the colder the air gets. When water vapor gets cold, it changes back into drops of water. If it gets

cold enough, the water changes to ice.

The water droplets and bits of ice are so small that they float on the wind. You see the water and ice in the sky as clouds

Strong winds and gentle breezes make different kinds of clouds.

WHAT ARE THE DIFFERENT KINDS OF CLOUDS?

Clouds that form in calm air look like flat sheets or layers of sheets. Clouds that form in strong winds tower up high in

the sky.

Meteorologists (scientists who study weather) group clouds into four families. Three families are called high clouds,

middle clouds, and low clouds. These three families form at three different levels in the sky. The fourth family is made

up of towering clouds that go up through the three levels. Meteorologists have grouped about 100 types of clouds intothese four families.

HIGH CLOUDS

High clouds are made of bits of ice. High clouds can be 5 miles (8 kilometers) or more above Earths surface. There are

three main types of high clouds. Cirrus clouds are thin and feathery looking. Cirrostratus clouds look like a misty, flat veil

or sheet. Cirrocumulus clouds look like groups of small, white cotton balls. Rain and snow do not fall from these clouds.

MIDDLE CLOUDS

Middle clouds are made of water droplets. They form about 2 to 4 miles (about 3 to 6 kilometers) up in the sky. There

are two main types of middle clouds. Altostratus clouds are like a gray or bluish sheet of frosted glass across the sky. You

can see through them, but they make the Sun and the Moon look blurry. Altocumulus clouds look like big wads of white

fuzz.

LOW CLOUDS

Low clouds are made of water droplets. Most low clouds are less than a mile (1.6 kilometers) high. There are three main

kinds of low clouds. Stratocumulus clouds are soft, gray rolls of clouds. They often cover the whole sky. Stratocumulus

clouds are not very thick, so blue sky sometimes peeks through the clouds. Nimbostratus clouds are thick, dark, and

shapeless. They are gloomy-looking clouds. Rain or snow usually falls from these clouds. Stratus clouds are really fog up

high. They look like gray blankets. These clouds often break up, letting you see blue sky beyond.

TOWERING CLOUDS

Towering clouds stretch through the low, middle, and high cloud layers. There are two main kinds of clouds in this

group. Cumulus clouds have flat bottoms and rounded tops that look a little like cauliflower. Cumulonimbus clouds are

dark, heavy-looking clouds. They rise up like mountains high into the sky. Sometimes the tops of these clouds spread out

at the top. The top is made of ice. Cumulonimbus clouds are also called thunderheads. These clouds bring

thunderstorms and sudden, heavy rains.



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THE SUN

The Sun, like other stars, is a hot ball of gas. Hydrogen and helium are the main gases in the Sun. Almost all the energy in

our solar system comes from the Sun. The Sun changes hydrogen into helium to create light and heat. These changes

take place deep inside the Sun.

THE NINE PLANETS

Eight of the nine planets in our solar system fall into two groups called the inner planets and the outer planets. The fourplanets closest to the Sun are called the inner planets. They are Mercury, Venus, Earth, and Mars. The inner planets are

also called the rocky planets, because they are made mainly of rock and iron. There are four outer planets: Jupiter,

Saturn, Uranus, and Neptune. The outer planets are also called the gas giants because they are huge and made mainly of

gas. Pluto, the farthest planet from the Sun is a small ball of ice. Some astronomers wonder whether Pluto should be

called a planet.

Mercury is the planet that is closest to the Sun. It has a large core, or center, that is made of iron. Venus, the next planet

from the Sun, is the hottest of the planets. The temperature on Venus is about 890 Fahrenheit (about 477 Celsius).

Earth is the only planet known to have life. It also has plenty of liquid water. There are signs that liquid water may once

have flowed on Mars, but now Mars is cold and dry. What happened to the water on Mars is a great mystery that

scientists are trying to solve.

Jupiter is the largest of the planets. A thick atmosphere made of hydrogen and helium surrounds it. Jupiters clouds look

like white, brown, and orange stripes going around the planet. There is an oval-shaped red spot in the clouds.

Astronomers think this spot is a big storm that has been raging for hundreds of years! Saturn is the second largest planet

and the sixth planet from the Sun. It has bright rings around it. Uranus and Neptune look like smooth blue balls.

Methane gas gives these planets their blue color. Pluto is the smallest planet in our solar system. It is far from the Sun

and very cold. Temperatures on Pluto can drop down to -387 Fahrenheit (-223 Celsius).

MOONS AROUND THE PLANETS

Seven of the planets have natural satellites, or moons. Mercury and Venus do not have any moons. Earth has 1 moon

and Pluto has 3. Mars has 2 moons. Neptune has 13 known moons; Uranus has at least 27 moons; Saturn has 47 moons;

Jupiter has at least 63 moons. Jupiters moon Io has active volcanoes.

ASTEROIDS, COMETS, AND DUST

There are thousands of asteroids in the solar system. Asteroids are small pieces of rock and metal. Most of them orbit

the Sun between Mars and Jupiter. Asteroids that crash into Earth are called meteors. Sometimes they burn up as they

fall toward Earth. They make streaks of light in the night sky. Pieces that land on the ground are called meteorites.

Comets are another type of object in the solar system. Comets are like dirty snowballs. They are made of ice and dust.

Comets are usually far out in the solar system. Sometimes a comet comes in close to the Sun. When it comes in close,

the comet starts to melt and looks like it has a long tail streaming out behind it. In 1994 pieces of a comet calledShoemaker-Levy 9 crashed into Jupiter. The crash made huge explosions and sent up fireballs that were larger than

Earth.

HOW DID THE SOLAR SYSTEM FORM?

Astronomers think that the solar system may have come from a swirling cloud of gas and dust. First a star, our Sun,

formed from a clump in the cloud. It began as a spinning ball of gas at the center of the cloud. Then the planets, their

moons, and the other objects in the solar system formed from the leftover gas and dust. Other stars and solar systems in

the universe may have formed the same way. In fact, new solar systems are still forming from giant clouds of gas and

dust.


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Also in Encarta


Comets are big chunks of ice and dust that go around the Sun. When comets come close to the Sun, they develop long,

bright tails. Sometimes we can see them from Earth.

Beyond the asteroid belt lie the outer planets. Jupiter, Saturn, Uranus, and Neptune are giant planets made mostly of

gas. They have no solid surface. Jupiter is the biggest planet in the solar system. More than a thousand Earths could fit

inside it.

Asteroids are big pieces of rock and metal in space. There are thousands of them between Mars and Jupiter in an area

called the asteroid belt. They go around the Sun just like planets do.

The inner planets are the four planets closest to the Sun: Mercury, Venus, Earth, and Mars. They all have hard, rocky

surfaces. Mercury and Venus get hot enough to melt lead, while Mars is colder than Antarctica. Only Earth is known to

have life and liquid water on its surface.

The Sun is the heart of the solar system. It is a stara huge ball of burning gases. Its tremendous heat and light make life

on Earth possible. The Sun is so big that a million Earths could fit inside it.

Our planet, Earth, is one of the planets in our solar system. The solar system is made up of the Sun and everything that

goes around it. In addition to the planets and their moons, the solar system includes asteroids, comets, and all the other

bits of rock, dust, and ice that circle the Sun.

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 doesnt 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.

WHATS 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


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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 Moons 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, youd 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 Moons

surface. It filled in low places, including some of the big craters. Then the lava cooled to make the Moons 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 cannever 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 dayhotter 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 thereabout -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 cant see any reflected sunlight. This is

called the new moon.


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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 isabout 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.


The Moon orbits, or circles around, our planet Earth. The Moon is made up of mostly rock and metal. It has no liquid

water, and no life. The Moon shines in the night sky because it reflects the light of the Sun. Just like Earth, half the Moonis always in sunlight. But from Earth, we see the entire sunlit side of the Moon only once each month, when we call it a

full moon.


In the mid-1900s, a biologist named Rachel Carson was afraid that some day there might be no more birds. Farmers

were spraying a chemical called DDT on their fields to kill insects. But DDT was also keeping birds such as the bald eagle

and peregrine falcon from having babies. DDT prevented the babies from hatching. She wrote a book calledSilentSpring

to warn about the dangers of DDT.

Pollution happens when chemicals that are harmful to living things get into the environment. Rachel Carson feared that

DDT would get into the food people ate. Her book scared a lot of people. Governments banned the use of DDT. People

then began to worry about other kinds of pollution. They worried that pollution could harm peoples health.

WHAT DOES POLLUTION DO?

Pollution can kill or sicken plants, animals, and people. Pollution can change the environment. Things that cause

pollution are called pollutants.

Pollution can get into the air. Air pollution can irritate peoples lungs. Polluted air can mix with rain to make acid rain.

Acid rain kills trees and harms fish in lakes.

Pollution can also get into soil and water. From there, pollutants can get into the food chain. Plants take in the pollution

from the ground. Animals that eat the plants can be harmed, too. Bigger animals and even people might eat the

damaged animals.

WHERE DOES POLLUTION COME FROM?

Air pollution comes from factories and power plants that burn coal and oil. Smoke from factories and power plants can

mix with water in the air to make acid rain. Air pollution also comes from cars and other vehicles that burn gasoline.


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Soil pollution can come from chemicals used on farms to kill insects and other pests. Pollutants can also seep from

garbage dumps into the nearby soil and water.

Water pollution comes from factories that dump poisonous chemicals into lakes and rivers. Water pollution can also

come from farms. Farmers put chemicals on the ground to help crops grow and to kill insects. Rain can wash these

chemicals into lakes and rivers.

Big ships called oil tankers can pollute the ocean if the oil leaks out of the tankers. There can be a huge oil spill if a tanke

has an accident and sinks at sea.

A special kind of pollution comes from nuclear power plants. Nuclear power plants produce radioactive waste. This

waste lasts for thousands of years and can cause cancer and other deadly illnesses if it is not properly stored.

IS POLLUTION CHANGING EARTHS CLIMATE?

Many scientists think that pollution is changing Earths climate. They think the change is coming from gases in the air

called greenhouse gases. Carbon dioxide and other gases trap heat from the Sun. They trap heat the way glass walls and

ceilings in greenhouses trap heat. It stays warm inside a greenhouse even when it is cold outside.

Greenhouse gases in the air make Earth warm enough for life. But scientists think that people are putting too muchcarbon dioxide and other greenhouse gases into the air. These extra greenhouse gases come from burning coal and oil in

factories and power plants. They come from burning gasoline in cars. Too much of them will make Earth warmer. This

warming could cause disastrous changes on the planet.

HOW CAN WE STOP POLLUTION?

Chemicals that cause pollution are not easy to get rid of. They stay in the air and ground and water for a long time. The

best way to fight pollution is to stop producing it in the first place. Governments can pass laws that forbid or limit the

use of chemicals that cause pollution. Laws can stop factories from dumping poisonous chemicals in lakes, rivers, and

the ocean. Factories and power plants can clean up the smoke that they give off.

Engineers can build cars that burn less gasoline. They can find ways for cars to give off cleaner exhaust gases.

Scientists are looking for fuels to replace coal and oil. They are looking for ways to use the power in wind and in rays

from the Sun. They are also looking for safe ways to get rid of nuclear waste.

You can help cut down on the amount of garbage you make. You can recycle paper, plastic, glass bottles, and metal cans

Recycled material gets used over again. Recycling helps cut down on pollution.

Also in Encarta Kids


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?


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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 STARS LIFE


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There are different stages in a stars 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 stars 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 andmake 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 morethan 4 light-years from Earth. A light-year is the distance light travels in a year, about 6 tri llion 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 astronauts lifetime. It takes billions of years for even light to reach the most distant stars.

Also in Encarta Kids


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 stara 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 Earths gravity holds you on the ground. The Suns gravity holds Earth and the other planets in their orbits. I

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

Suns 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.


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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 Suns 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 Suns 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 Suns atmosphere. The corona is so faint tha

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 l igh

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 dont need to worry. Astronomers say that the

fuel will last several billion more years.

Also in Encarta


Heres a riddle: How is heat like a river? Answer: They both flow downhill. You will never see a river flow up a

mountain. A river only goes one way, down. Heat also goes one way. Heat only flows from something that is hotter to

something that is colder.


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You might think that putting an ice cube in your lemonade makes the lemonade cooler. What really happens is that the

lemonade makes the ice cube warmer. Heat goes out of the warmer lemonade into the colder ice cube. Heat only flows

one way.

WHAT IS HEAT?

Heat is an important kind of energy. Heat from the Sun makes life on Earth possible. Heat makes your home warm. Heat

cooks your food. Heat makes cars go. You use more heat than any other kind of energy.

Things that make heat are called heat sources. The Sun is a heat source. Fire is a heat source. Melted rock and metal

inside Earth are sources of heat. Heat sources make other things hot.

WHY DO THINGS GET HOT?

Things get hot because tiny bits of matter called atoms and molecules move around. Everything is made of atoms or

molecules. They are much too small for you to see.

Atoms and molecules are always moving around. They move around slowly in something that is cold. They move around

quickly in something that is hot. Heat energy comes from moving atoms and molecules.

An iron frying pan is made of iron atoms. Heat energy from a fire makes the iron atoms move faster. The atoms bang

into one another. The faster the atoms whiz around, the hotter the frying pan gets. The hot frying pan in turn makes

things like strips of bacon hot.

HOW DOES HEAT MOVE?

Heat energy can move in three ways. These three ways are called conduction, convection, and radiation. Conduction

carries heat through things that are solid. The frying pan heats the bacon through conduction.

The frying pan sits on a flame. Heat from the flame makes atoms at the bottom of the pan move faster. The atoms on

the bottom bang into the atoms above them. This makes those atoms move faster and bang into more atoms. As atoms

bang into other atoms, the heat energy travels from the bottom of the frying pan to the top. The heat energy enters the

bacon and cooks it to a crisp.

Convection heats liquids and gases. A radiator heats air in a room by convection. Air near the radiator gets hot. Hot air

rises. Cooler air replaces the heated air. This air gets hot and also rises. The air keeps going around and around from

cooler to hotter. The way the air moves is called a convection current.

Radiation can send heat across empty space. This is how heat from the Sun travels to Earth. Heat rays from the Sun

strike the surface of Earth and make it warm.

WHAT IS TEMPERATURE?

Temperature and heat are not the same thing. Temperature is a measurement of heat. Temperature tells whether

something is hot or cold.

You measure temperature with a thermometer. A thermometer has a scale, such as Fahrenheit or Celsius. A

thermometer hanging outdoors measures the temperature of the air. Air that is 32 Fahrenheit (0 Celsius) does not

have much heat energy. At that temperature, water can freeze into ice. Air that is 100 Fahrenheit (38 Celsius) can

make you feel very warm. Better put some ice into your lemonade and try to cool off!



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The blade is the part of the leaf that catches sunlight, which is used to make food for the plant. The blade has tiny

openings to allow water and gases to enter and leave the plant. Blades come in many shapes and sizes.


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Veins move water from the plant to the leaf and carry food made in the leaf to the rest of the plant. Many leaves have

one large vein that runs down the center of the blade, with small veins branching off it.

The petiole attaches the leaf to the plant. It also moves the leaf into the best position for receiving sunlight.

Petals are often colorful and come in many shapes and sizes. Petals attract insects, birds, and other animals to the

flower in search of food known as nectar. These animals help pass pollen, a yellow powder, from the stamen (male parts

of the flower) to the pistil (female parts of the flower). Pollen contains male reproductive cells, or sperm.

The stamen contains the male reproductive parts of a flower. It is made up of an anther and a supporting tube known as

a filament. Pollen, a yellow powder that contains male reproductive cells (sperm), is made in the anther.

The pistil contains the female reproductive parts of a flower. It is made up of the stigma, style, and ovary. The stigma is a

sticky cap that traps pollen, a yellow powder containing male reproductive cells, or sperm. The style is a long tube that

carries pollen to the ovary. The ovary stores female reproductive cells, or eggs. When a sperm cell joins with an egg in

the ovary, a new seed forms.

Sepals are small leaves that grow around the base of the flower. Sepals protect a flower before it blooms, or opens.

Plants need sunlight. Houseplants lean toward the Sun, and if they do not get enough light they wither and die. Plants

use sunlight to make their food. This process is called photosynthesis.

Photosynthesis is a scientific word made up from Greek words. These words mean putting things together using light.

Inside plants leaves, light causes air and water to combine to make new chemicals. These chemicals are food for the

plants.

FOOD FACTORIES

In most plants, photosynthesis takes place mainly in the leaves. Like other living things, plants are made up of tiny cells.

The cells in a plants leaves contain even smaller, disc-shaped parts called chloroplasts. Chloroplasts are the food

factories where photosynthesis happens. A leaf the size of your little fingernail contains more than 10 million of them.

Chloroplasts contain a chemical called chlorophyll, which is bright green. Chlorophyll gives plants their green color and

makes photosynthesis work.

THREE INGREDIENTS


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For photosynthesis to work, the chloroplasts need to collect three ingredients: sunlight, air, and water. Sunlight shines

on the leaf, and the green chlorophyll inside the chloroplasts soaks it up. Air enters the leaf through tiny holes in the

leafs surface, called stomata. Water is sucked from the ground by the plants roots. It travels through tubes in the stem

or trunk to the leaves.

When all three ingredients are present inside the chloroplasts, a chemical reaction takes place. The reaction takes place

between a gas in air called carbon dioxide and hydrogen, a part of water. Sunlight causes these two to combine and

make new chemicals called carbohydrates. Carbohydrates are plant food. Plants use these chemicals to l ive and grow.

THE KEY TO LIFE

Photosynthesis is not just important for plantsit is the key to life for all of us. Plants use photosynthesis to make food.

We eat the leaves, roots, fruits, and seeds of plants. Spinach and lettuce are leaves. Potatoes and carrots are roots.

Tomatoes and apples are fruits. Nuts are seeds. If you eat beef, lamb, or other meat, you still depend on plants. Meat

comes from cows, sheep, and other animals that feed on plants.

In this way, energy from the Sun is passed on through all the different living things on Earth. If it were not for

photosynthesis, plants would not grow. There would be nothing for animals to eat, so they would not exist either.

BREATHABLE AIR

Photosynthesis also produces a gas, oxygen. Plants release oxygen into the air. Humans and other animals need oxygen

to live. We breathe in the oxygen produced by plants during photosynthesis.


Chloroplasts

Chloroplasts are tiny, round, green food factories within the leaves of a plant. During photosynthesis, they use energy

from sunlight to turn chemicals in air and water into plant food.

Richard Kirby/Oxford Scientific Films



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Stomata

Stomata are tiny holes in the surfaces of leaves. Stomata take in carbon dioxide and let oxygen out into the air during

photosynthesis.

Dr. Jeremy Burgess/Science Photo Library/Photo Researchers, Inc.


Flower

Some plants have flowers. These structures contain the reproductive organs of the plant. In nonflowering plants, such as

pine or juniper trees, the reproductive organs of the plant are found in cones.

Leaf

Leaves grow from the plants stem. Leaves collect energy from sunlight and change it into food.

Fruit

Some plants produce fruit, which contains seeds. Fruits protect the seeds until they are ready to grow into new plants.

Some fruits are tasty, such as tomatoes, apples, and oranges. Other fruits should not be eaten, including cotton and

milkweed.

The stem supports a plant and helps give it shape. The stem also moves water from the plant's roots and food from the

leaves to the rest of the plant.

A plants roots collect and store food and water from the soil and anchor the plant in the ground. Most roots grow

underground.

butterfly cycle

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