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World and Space

Childcraft
THE^HOW AND WHY LIBRARY
VOLUME 4

World and Space

World Book, Inc.

a Scolt Felzer company

Chicago London Sydney Toronto

1992 Edition
Childcraft The — How and Why Library
(Reg. US Pat. OH.)
(8 1991 World Book. Inc. All rights reserved. This

volume may not be reproduced in whole or in part in any

form without prior written permission Irom the publisher.

World Book. Inc.

525 West Monroe

Chicago. IL 60661

IB 1990. 1989.1987, 1986. 1985 by World Book. Inc c 1982. 1981.

1980. 1979 USA by World Book-ChildcraH International. Inc 6

1976. 1974. 1973, 1971, 1970. 1969, 1968, 1965, 1964 USA by
Field Enterprises Educational Corporation.

International Copyright c 1987. 1986. 1985 by World Book. Inc

International Copyright 5 1982, 1981, 1980. 1 979 by World Book-
Childcraft International, Inc
International Copyright O 1976, 1974. 1973. 1971, 1970, 1969. 1968.
1965. 1964 by Field Enterprises Educational Corporation.

ISBN 0-7166-0191-5
Library of Congress Catalog Card Number 90-701 78
Printed in the United States of America
A'lB

Acknowledgments

The publishers of Childcraft —The How and Why Library

gratefully acknowledge the courtesy of the following
publishers, agencies, authors, and organizations for
permission to use copyright material. Full illustration

acknowledgments appear on pages 328-329

John Ciardi: "Why the Sky Is Blue. S 1974, John Ciardi.

Photograph Japanese helmet, page 75, by

of

Jonathan Norton Leonard and the Editors of

Time-Life Books, 6 1968 Time. Inc

Photograph of Mars, page 248. and photograph of the

Great galaxy, page 280, e California Institute of
Technology and Carnegie Institution of Washington,
from Hale Observatories
Volume 4

World and Space

Contents
Our Home, the Earth 5
Our world is a ball of rock and metal, spinning in space

Mountains, Valleys, and Plains 21

The features of the earth's surface, and how they came to be

Rocks, Stones, and Petrified Bones 59

The things the earth is made of, and how we use them

Oceans, Lakes, and Rivers . Ill

The water that lies in and upon the earth's surface

Air, Wind, Clouds, and Weather 145

Earth's atmosphere — what it is and what it does

Planets, Stars, and Galaxies 203

Our near and far neighbors in space

Where in the World? 287

Maps, globes, and compasses, and how to use them

People Who Study the World and Space 305

The work of geologists, astronomers, and other scientists

Books to Read 322

New Words 324

Illustration Acknowledgments 329

Index .............. 331

Our Home,
the Earth
An island in space
We live on an island. An island in space!
An island is a piece of land with water all around it.

The earth is a giant ball of rock and metal with space

all around it.

A ball of rock and metal such as the earth is called

a planet. Planets are the "prisoners" of stars. They circle

around and around the stars they belong to. Earth is

one of nine planets that circle around and around our

star, the sun.
The sun is an enormous ball of hot, glowing gas. To
us, the earth seems big, but it's small compared to the
sun.The sun is bigger than a million earths!
The earth has one near neighbor, the moon. The
moon is a ball of rock, like earth, but much smaller. It
 Our Home, the Earth I 7

circles around earth just as earth circles around the

sun.
The moon is thousands of miles (kilometers) away
from the earth. The sun and the other planets are
millions of miles away. And the stars that you see
twinkling in the sky at night are trillions of miles
(kilometers) away. So, the earth is really a tiny island

in the great, black emptiness of space. But for us,

it's the most important place of all. It's our home.

•'•'•

A-/
 .-"."-

..it
The spinning world
You may think our world, the earth, is standing
still. But it isn't. The earth is spinning around and
around, like a huge top.
Push a stick through a ball of clay and then twirl

the stick. The clay ball will turn around like a wheel.
That's how the earth spins— around a kind of imaginary
axle that runs through its middle. This imaginary axle
is called the axis. One end of the axis is the North
Pole and the other end is the South Pole.
Why can't we feel the earth turn? Because we're so
tiny and it's But we know it does turn because
so big.
that's what gives us our day and night. In the morning,
when the sky is bright, we know that our part of the
earth is turned toward the sun. In the evening, when
the sky grows dark, we know that we've turned away
from the sun.
The time it takes the earth to make one complete
turn is just a little less than 24 hours— one full day
and night.
10

Around and around the sun

The earth doesn't just spin — it also moves through
space.
Right this very moment, the earth is rushing through
space at tremendous speed —more than 66,000 miles
(106,000 kilometers) an hour. It isn't going in a
straight line, though. It's whirling around and around
the sun, in a kind of stretched-out circle. This circle

makes around the sun is called an orbit.

the earth
What makes the earth keep moving around and
around the sun? Why doesn't it just fly off into space?
 Our Home, the Earth 11

Everything in space pulls at everything else. This

pull is called gravitation. The bigger a thing is, the
stronger its pull. The sun is more than a million times
bigger than the earth, so it tugs hard at the earth.
It is this strong tug that keeps the earth in orbit. If

you fasten some string to a ball, you can whirl the

ball around and around, to show the way the earth

goes around the sun. The string is like the pull of the
sun's gravity — it holds onto the ball. Even though the
ball is moving, it can only move in a circle.

The time it takes the earth to go all the way around

the sun is a little more than 365 days. This is what
we call a year.
mn

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 Our Home, the Earth 13

How was the earth born?

Why is the earth shaped like a ball? Why isn't it

shaped like a block? Or why isn't it round and flat,

like a pie? Why does it spin? And why does it whirl

around and around the sun?
Most scientists think that the answers to these
questions are part of the story of how the earth was
born. They think it is a story that began billions of
years ago, with a giant, spinning cloud in space.
There are many such clouds in space right now. They
are made up of chemicals in the form of gas and dust.
Scientists have found that some of these clouds seem
to be turning into new stars. And scientists think that,

about five billion years ago, our sun and its planets
were formed from just such a cloud.
The cloud was hundreds of millions of miles
(kilometers) wide! The force of gravitation pulled it

into the shape of a huge, flat wheel. And it spun

around and around, just like a wheel.
Gravitation slowly pulled the cloud together. Most of

the gas collected in the middle of the cloud. It formed

a lump that got bigger and bigger. As the lump grew,
its gravity became stronger. Then it pulled more and
more gas into itself. Because gravity pulls equally
from all directions, the lump was squeezed into the
shape of a round ball. This was the only shape it could
take.
After a long while, there was a gigantic ball of gas
in the middle of the wheel-shaped cloud. This was the
beginning of the sun.
14

1. A gigantic cloud of dust

and gas drifted in space.

Gravity pulled much of the

gas into a huge ball in the
cloud's center. This was the
beginning of our sun.

Farther out, in the rest of the cloud, other balls

were forming as gravity pulled bits of dust and gas
together. After a while, most of the cloud was used up.
There were only balls of gas and dust, whirling around
the sun.They were spinning and moving around the
sun because the cloud they were made from had been
spinning. These balls were the beginning of the earth
and the other planets and moons. So that is why the
earth is a spinning ball that whirls around the sun.
But if the earth was once a spinning ball of dust
and gas, how did it become a ball of rock and metal?
As earth's gravity pulled more dust and gas in,

everything was squeezed together — tighter and tighter

and tighter! This made the ball grow hotter and
hotter! It became so hot that the bits of dust in it,

which were mostly rock and metal dust, melted

together. The earth became a glowing ball.
But the outside of the earth couldn't stay hot. It

began to cool. And when melted rock and metal cools,

 Our Home, the Earth I 15

2. In other parts of the

cloud, gravity pulled
dust and gas together
forming blobs.

3. The blobs of dust and

gas slowly shrank into
tight-packed balls. This
was the beginning of the

earth and other planets.

it gets hard. So the earth became a ball of hard rock

and metal, as it is today.
But the earth still hasn't cooled off. The middle is

still fiercely hot, and part of the inside is still melted.

There are many other beliefs about how the earth was
born. The book of Genesis in the Bible says
that God created the earth and all living things. But
no one actually knows how it happened.
16

crust

mantle

outer core

inner core
 Our Home, the Earth 17

What's inside the earth?

Could you dig a hole to the other side of the earth?
No, you couldn't. The center of the earth is about
4,000 miles (6,400 kilometers) beneath your feet. So,
it's almost 8,000 miles (13,000 kilometers) to the other
side of the earth. You couldn't dig that far. And for

most of that distance, the earth is either solid rock or

metal so hot that it's melted! You certainly couldn't dig

through that!
When the outside of the earth cooled, it became a
kind of shell of rock. We call this the crust. The oceans
and the continents lie on top of the crust. Beneath the
oceans, the crust is about five miles (8 kilometers)

thick. Beneath the land, it is about twenty-five miles

(40 kilometers) thick.
Under the crust there is another layer of rock called
the mantle. The mantle is made of a different kind of
rock than the crust. The deeper the mantle goes, the
hotter it gets. It is about 1,800 miles (2,900 kilometers)

thick. At its bottom, it is hot enough to melt iron.

Beneath the mantle is a layer of melted metal
metal so hot that it's like thick syrup! This layer is

called the outer core. Scientists think the outer core is

made of iron and nickel and is about 1,400 miles (2,250

kilometers) thick.
In the center of the earth is the inner core. It's a
ball of hot, solid, squeezed-together metal about 1,600
miles (2,570 kilometers) thick.
That's what's inside the earth.
18

The outside of the earth

We live on the surface of the earth. The surface, or

crust of the earth, made of rock. In some places,
is

it is covered with soil. In many places, it is covered

with water. All around it is air.

Some of us live on huge pieces of land called

continents. A continent is like a great platform of

rock that sticks up a little higher than the rest of the
rocky crust.
Some of us live on smaller pieces of land called
islands. An island is the top of an underwater mountain
or part of a continent that has become separated
from the rest of the continent.

The continents and islands where we live are

 Our Home, the Earth I 19

surrounded by water. Water covers nearly three-fourths

of the crust of the earth. Most of this water lies in

enormous pits that are like great bowls in the rocky

crust. These huge "bowls" of water are the oceans.
Water also lies in smaller pits in the continents and
islands. These inland pits of water are lakes and
ponds. Water also flows in rivers and streams, from the
high parts of the land down to the lakes and seas.

All around the surface of the earth is a layer of air.

This layer of air is hundreds of miles (kilometers)

high. The air is thickest next to the land and water.

It gets thinner the higher it goes. Where the air comes
to an end, outer space begins.
So that's our earth —a big, spinning, moving ball

of rock and hot metal, with a thin coating of soil,

water, and air on the outside.

J?"ft2
 21

Mountains,
Valleys,
and Plains
200 million years ago

135 m

today
 Mountains, Valleys, and Plains 23

The moving continents

may seem to you that the earth's crust is
It a single
piece of rock. You may think this crust covers the outside
of the earth just as an apple's skin covers an apple. But
the earth's crust is actually made up of a number of
enormous separate pieces, called plates. These plates fit

together, like the pieces of a puzzle. And they are all

moving, very slowly, in different directions.

Scientists are not sure what makes these huge,

curved sheets of rock move. They think the plates slide
on the hot, soft rock beneath them. The plates move
from less than one inch (2.5 centimeters) to eight
inches (20 centimeters) a year.
Some of the plates make up part of the ocean floor.

Others hold the high masses of rock that rise above the
sea and form the continents. As the plates move, they
carry the continents and ocean floor with them.
The plates have probably been moving for billions of

years. This means that the earth's continents and seas have
probably had many different shapes. Scientists think
that more than two hundred million years ago the earth's
dry land was all bunched together, forming one gigantic
continent. Slowly, as the plates moved, the one huge
continent broke into two continents. And, as the plates
continued to move, both of these continents broke up
to form the seven continents we know today.
As the plates keep moving, the continents and seas
will keep changing shape. Scientists think that in about
fifty million years South America and Africa will be
farther apart than they are now. This will make the
Atlantic Ocean wider. And Australia may move up and
push against Southeast Asia, becoming part of it.
 Mountains, Valleys, and Plains 25

Giant rocks

Mountains are like great, gray giants.

They are huge chunks of rock that have
been pushed up out of the earth. Some
mountains stand all alone, but most are
connected together. Long chains of
connected mountains are called mountain
ranges.
Mountains are not all alike. Many
mountains are bare and rocky. Others
have green forests and fields of grass

growing on their sides. And most high

mountains have snow on their tops all

year round. This is because the air at the

height of a mountaintop is usually cold

enough keep water frozen.

to
Scientists believe that most of the
earth's mountains are many millions of

years old. The newest are wrinkled, and

have sharp, pointed tops. Older

mountains are smooth, with rounded

tops. These "old" mountains have been
worn down by wind and rain during

many millions of years.

Cascade Mountains, Washington

26

Some mountains are bare and rocky.

Others are green with grass and
trees. Newer mountains are sharp
and pointed. Very old mountains are
smooth and rounded by erosion.

Snowy Mountains, Australia

 Mountains, Valleys, and Plains I 27

Mount Rundle, Alberta, Canada

28

The birth and death

of a mountain range
Mountain ranges rise where a sea once met a shore.
They start to form when a sea bottom along the edge
of a continent begins to up with mud and sand. As
fill

the mud and sand grow thicker, the sea bottom begins
to sink. The mud, sand, and rock drop slowly down
into the earth's mantle — the hot rock beneath the crust.
They are crushed, squeezed, and melted together by
heat and pressure. Hot rock from the mantle is mixed
in with them. All this takes many millions of years.
Mountains are born when this mixture of rock is

pushed up again by earthquakes and other forces in the

earth. As the huge pile of rock rises, it pushes the

edge of the land into wrinkles and folds. After many
more millions of years, the upper part of the long,
lumpy mass of rock has risen high above the land.
Mountains now sit where once the sea met the shore.
As soon as mountains are born, they begin to wear
down. Rain falls on them. Each drop, like a little bomb,
breaks off tiny bits of rock. Wind blows off tiny grains
of rock and carries them away. Streams and rivers run
down the slopes, cutting great grooves. Sometimes, huge
masses of ice and snow move down mountainsides,
grinding the rock to powder.
For millions of years, all these forces wear tons
and tons and tons of rock from mountains. Slowly, the
proud, peaked mountaintops are worn down and
smoothed out. After many millions of years, nothing is

left of a mountain range but a row of small, smooth

hills. After more years, even those are worn away.
 Mountains, Valleys, and Plains I 29

Mountains begin to form on a sea bottom

hundreds of millions of years ago.
mat

During millions of years, mud, sand, and

hot rock are mixed together and pushed
up out of the sea bottom. This forms a
long chain of wrinkled mountains.

During many millions of years, wind, rain,

and snow slowly wear down mountains.
 Mountains, Valleys, and Plains I 31

The highest place

in the world

Where do you think the highest place

in the world is?

As you may have guessed, the highest

place in the world is the top of a
mountain. It is the top of Mount Everest,
which stands between the countries of

Tibet and Nepal, in Asia.

When we want to find out how high a
mountaintop is, we can't just measure the
mountain —we have to measure all the
land it's sitting on, too. To do that, we
must go to where the land begins at the —
top of the sea. That way, we can measure
all the land that slopes up from the
sea to the very top of the mountain.
When we measure something this way,
we are measuring from sea level. All the
land in the world is either above or
below sea level. The top of Mount Everest,
the highest place in the world, is 29,028
feet (8,848 meters) above sea level.

On May 29, 1953, Sir Edmund Hillary

of New Zealand and Tenzing Norgay of
Nepal became the first men to climb to
the top of Mount Everest. Since then,
many other climbers have made it to the
"top of the world."

Mount Everest, between Nepal and Tibet

32 I Mountains, Valleys, and Plains

Mountains of fire
A volcano is a special kind of mountain that actually
builds itself! It is made of red-hot rock that pours up
out of the earth amid earthquakes, explosions, and
towering clouds of smoke and ash.
Scientists think that far down in the earth, where
it is fiercely hot, there are "pockets" of melted rock.
It is thought that the pressure of gas pushes this
melted rock, called magma, up out of the ground.
When magma comes out of the ground it is called lava.
It may be as thick as syrup or as thin as watery soup,

but it cools into a black, gritty rock. It is this rock

that builds the volcano. As the lava pours out of the

earth, it piles up into the shape of a cone or dome, with

a tunnel running down its middle. The more lava that
comes out, the higher and wider the volcano gets.

After a volcano has built itself, it may sit quietly

for hundreds or even thousands of years. Then,
suddenly, the volcano becomes active. The ground
begins to shake. Rumbling noises come from deep
inside the earth. From the top of the volcano, clouds of
dark smoke twist up into the sky. The rumblings
become a loud, steady, rushing roar. Magma or hot
gas comes surging up through the tunnel. It may burst
out of the top of the volcano or flow out of cracks in
the side. The volcano has erupted!
There are different kinds of volcanoes that erupt
 te

0:9

Mount Hekla, Iceland

hot lava

cooled lava

in different ways. One kind shoots a stream of glowing

lava high into the air, like a giant, fiery fountain.
Another kind shoots out solid chunks of red-hot rock

and Some volcanoes pour rivers

cinders. of lava

through cracks in their sides. Some send clouds of

glowing, super-hot steam and gas rushing down the
mountainside. And some blow themselves to pieces
when they erupt!
There are several thousand volcanoes in the world.

Many of them do not seem able to erupt any more, and

 Mountains, Valleys, and Plains 35

are called "dead" volcanoes. But some volcanoes that

have been "dead" for hundreds of years have suddenly
become active and had terrible eruptions. And active
volcanoes are liable to erupt at any time. Volcanoes
have killed many people and destroyed whole cities.

But volcanoes have done good things, too. The ash

that comes from volcanoes becomes some of the richest,

most fertile soil in the world. And scientists think that,

billions of years ago, much of the earth's first air and

water came from gas and steam spouted from volcanoes.
36

When the earth shivers

"The mountains seemed to walk!"

That is what a Chinese writer said about a terrible

earthquake he saw. During the worst earthquakes, the

ground shivers and shakes and rumbles. Whole sections
of land get pushed out of place, so that mountains
truly seem to "walk."
Earthquakes begin in the earth's rocky crust. Pressure

earthquake damage, San Francisco

 Mountains, Valleys, and Plains | 37

builds up and begins to push. The force of this push

actually bends the rocks, just as you bend a stick.
And, suddenly, the rocks snap and break, just as the
stick would snap if you kept bending it. This sends
shivers through the ground making it quiver and quake.
Earthquakes are actually happening all the time.
Every few minutes there is one somewhere in the world.
Sometimes an earthquake is very powerful and does a
lot of damage. But most earthquakes are so slight they
don't even rattle a spoon in a teacup.

It's a Fact

Every two or three minutes

there's an earthquake
somewhere in the world.
V) The earth is always shivering!
 I
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 Mountains, Valleys, and Plains I 39

Nature's ditches

What parts of the earth's surface have floors

and walls?
Valleys. A valley is like a long ditch scooped out of
the ground. The bottom of the ditch is called the

floor.The sides are called valley walls.

Some valleys are places where the ground has sunk.
But most valleys are made by rivers and streams. As
water flows along, it tears away bits of the land. As
years go by, more and more land is worn away. The
river sinks deeper and deeper. Steep walls form on both
sides of it. Then wind and rain begin to wear away
the walls, making the valley wider. In time, the valley
becomes a long, V-shaped ditch, with the river or
stream flowing along the floor.

Some valleys have grown so wide that they are no

longer V-shaped. Some are U-shaped. Others have
become deeper rather than wider. Very deep valleys
with steep walls are called canyons or gorges.

Oneonta Gorge, Oregon

40 I Mountains, Valleys, and Plains

A valley is like a long ditch scooped out

of the ground. Most valleys are made by
rivers that carry away tons of rock and
dirt every year. During many thousands of

years, the valley grows deeper and

broader. Valleys with very steep walls
are called canyons or gorges.

Rhone Valley, Switzerland

Canyon de Chelly, Arizona
 ',ii^;;;:: ^:J .
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Dead Sea, between Jordan and Israel

The lowest place

in the world

If the highest part of the land is a mountaintop,

where do you think the lowest place must be?
That's right — in a valley.

The lowest bit of dry land in the world is the Valley

of the Dead Sea, between Jordan and Israel. The land
there is 1,312 feet (about 400 meters) below the level of
the nearby Mediterranean Sea.
The Valley of the Dead Sea was not made by a
river, as many valleys are. It is a fault — a large strip

of the earth's crust that has sunk down.

 Mountains, Valleys, and Plains I 43

Open country
All over the earth there are great flat places. The
level or gently rolling land goes on for miles (kilometers).
These flat parts of the earth are called plains.
Most plains are lower than the land around them.
It might seem, then, that plains would be on the lowest
parts of the land. But this is not always so. Coastal
plains are low, and usually slope gently upward from
sea level. But inland plains, such as the Great Plains
in the United States, are often thousands of feet
(meters) above sea level.

Serengeti Plain, Tanzania

4T
 m

n
an oasis in the Sahara, Algeria
 Mountains, Valleys, and Plains |
45

Dry lands
The golden, glowing sun glares down on a vast sea of
sand. As far as the eye can see, the sand stretches
in great yellow-brown ripples. The air is so hot you can

see it shimmer as it rises from the sand. There is not

even the tiniest green plant anywhere in sight.

Whenever most people think of a desert, they usually

think of an endless, hot sandy land. But there are
actually many different kinds of deserts.

Some deserts are rolling, sandy places where hardly

any kind of plant can grow. Some are flat plains that

are covered with many kinds of plants. Even the

world's biggest, hottest desert, the Sahara, has small
patches of trees and grass in some places. Such a patch
of greenery is called an oasis.

Some deserts are hot all year round. Others are hot
in the summer and cold in the winter. Some deserts are
great bare places on the shores of seas. Others are
rocky places high up in mountains. But all deserts,
wherever they may be, are the earth's dry places-
places where little rain falls.

does rain in deserts, but usually only a tiny bit.

It

Some parts of deserts go for many years without rain,

then get just a sprinkle. Sometimes a desert is so hot
that the rain dries up before it reaches the ground!
But some deserts get cloudbursts. Then, rain pours
down on parts of the desert. In fact, the heavy rain
may cause sudden floods. The dry earth can't soak
up the water fast enough, and water quickly fills

up the desert's low places. But, soon, the ground is

again as dry as an old bone.

46 I Mountains, Valleys, and Plains

Scientists can tell that the deserts now on earth

were not always here. Most of them are probably only
a few million years old. At one time, most of the

places we now know as deserts were green and fertile.

But something happened. Changes in the wind and

weather made rain stop falling on these places. Then,
year after year, these lands were baked and dried by
the sun until they became the deserts they are today.
 '*
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Nullarbor Plain, Western Australia

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It's a Fact

The highest temperature of

Atacama Desert, Chile
anyplace in the world was
recorded in the Sahara
a temperature of 136 degrees
Fahrenheit (58° Celsius).
48

<0

&*Mrw

Land in the water

Explosion after explosion of hot rock and ash spurted

from the ocean. A thick cloud of steam rose high into

the air. Slowly, for many days, a long mound of dark

lava rose up out of the water. An island had been born!
An island, of course, is a piece of land with water all

around it. But the land doesn't float on the water.

What you see is the top of land that sticks up from the
bottom of the sea. Most islands far out in the ocean are
actually the tops of underwater volcanoes!
Volcanic islands are made when underwater
volcanoes erupt, pouring out red-hot, melted rock. The
rock quickly cools and hardens in the water, building
up into a big, cone-shaped mountain. The island is the
top of the cone.
All islands aren't volcanoes. Most islands in lakes and

rivers are high pieces of land that stick out of the water.
Some islands are formed when the sea separates them
from the mainland. Great Britain was not always an
island. At one time, a low plain joined it to Europe.

Thousands of years ago, the sea covered this plain.

 Mountains, Valleys, and Plains |
49

island of Surtsey, Iceland

Most islands in the ocean are the tops

of underwater volcanoes. The picture
at left shows such an island being
born. Smoke from the underwater volcano
is pouring up. Below, the top of the
volcano has risen from the water.
50

Lands of ice

Two parts of the earth are bitter cold all year

round. These places are the "top" and the "bottom"
of the earth —the North Pole and South Pole.
The land around the South Pole is called Antarctica.
It is the coldest place on earth. Antarctica is covered
with a sheet of ice more than a mile (1.6 kilometers)
thick. But beneath the ice there is land, just like

other land, with mountains, plains, and valleys.

At the North Pole there is no land. This part of
the world is just a huge sheet of ice from four to ten
feet (1.2 to 3 meters) thick. Beneath the ice there is

only the water of the Arctic Ocean.

Beaufort Island, Antarctica

 Mountains, Valleys, and Plains I 51

Scientists know that ten or twenty million years

ago there was no ice at the North and South poles!
Palm trees grew in Antarctica, and animals such as
those that now live only in hot places lived there!
But something happened to turn the two poles into
regions of ice.

We know why the poles became covered with

don't
ice, but we know why the ice does not melt. It is

because the sun never shines directly down on the

poles. Because the sun is usually low in the sky, the
air stays cool. Thus, the poles get much less heat than
the rest of the earth. And most of the heat they do
get bounces off the shiny, white ice and is reflected
back out into space. So the poles never get enough
heat to melt all the snow and ice.

It's a Fact

The lowest temperature of

anyplace in the world was
recorded in Antarctica
127 degrees below zero,
Fahrenheit (-88° Celsius).
glacier, Chile

Icy bulldozers

Some snow on a high mountaintop melts and

of the
runs off. But much of it stays all year round. The snow
that stays becomes hard and grainy, like salt. As new
snow falls each year, the grainy snow underneath is

squeezed together and becomes hard as ice.

The weight of all the snow pressing down squeezes

out a stream of ice, like toothpaste is squeezed from a
tube. This gigantic stream of ice, creeping down the
mountainside, is called a glacier.
 -J •

V :v .

There are two main kinds of glaciers. One kind is

like a river of ice. It stretches from near the top of a

mountain down into a valley below. The other kind of
glacier is like an enormous cake of ice and snow. This
kind covers whole mountain ranges and even whole
lands. All the land at the South Pole is covered by such
a glacier.
Most glaciers move slowly. They travel from only a
few inches (centimeters) to about forty feet (12 meters)
a day. But, slow as it is, a glacier is like a big, icy
bulldozer. It scrapes, gouges, and shovels up the
ground over which it moves. It picks up everything
A snow on
glacier begins as a pile of
a mountaintop. The snow at the bottom
of the pile becomes ice. The ice

slides slowly down the mountainside.

As a glacier moves, it gouges out

tons of rock and widens the valley
it passes through. Many valleys were
made wider by glaciers that covered
northern parts of the world long ago.
 Mountains, Valleys, and Plains |
55

boulder left by a glacier,

Tasmania, Australia

SHI
lake made by a glacier, New York

in its path, from soil to huge boulders, and carries it

along. As a glacier passes through a valley, it may dig

the valley deeper and wider. As moves down ait

mountainside, it may leave long scratches and furrows.

Glaciers make valleys wider and dig out holes for
lakes. Long ago, during the time that is called the

Ice Age, great glaciers crept far across the land. They
dug many ditches and deep holes in some of the places

they passed over. Later, these holes filled up with

water and became some places the glaciers
lakes. In

left rich soil that they had picked up as they moved.

In other places, they left behind huge boulders that now
sit far from the mountains that were once their home.
Soil, sand, and dust

Tiny chips of rock and powdered flower petals. Bits of

bats' wings and birds' feathers. Fragments of dried-up
caterpillar skin and pieces of mouse whiskers.
That isn't a recipe for a magic potion. It's the "recipe"
for soil! Soil is tiny bits of rock mixed with tiny bits of

dead plants and animals. When plants and animals die,

their bodies decay and fall apart. Rain washes them into

the ground, to mix with the rest of the soil. >: f *(

Sand is tiny bits of rock. Wind, water, and the roots of

plants all help to make sand. Wind blowing against rock
wears off tiny bits of it. Rain falling on rock, and waves
smashing against it, also break off bits. The roots of
plants dig into rock and split it into small pieces.

Dust is made up of tiny, tiny bits of sand, soil, animal

hairs, bits of plants, and other things carried into the air

by the wind. The dust floats in the air for a time, then
drifts back to earth again.
 ir
mm ' *

"'* 7 » - v
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sand

dust

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 59

Rocks,
Stones, and
Petrified Bones

(j\
lT'~jSiLjg)
 Rocks, Stones, and Petrified Bones I 61

The rock factory

The earth is a rock factory. Scientists believe it has
been making rocks for billions of years.

The earth makes three different kinds of rocks. One

kind is made from hot, syrupy liquids, deep inside the
earth. Sometimes, some of this liquid rock pushes its

way between two layers of solid rock —making a sort of

rock sandwich. Then the liquid cools off and becomes
solid, too. Sometimes, when volcanoes erupt, some of
the liquid rock is pushed up out of the earth. When it

reaches the earth's surface, it cools and becomes solid.

Rock that was once a hot liquid is called igneous

rock. Igneous means "of fire." Granite, the hard,
light-colored sparkly rock used on the outside of many
buildings, is an igneous rock. And so is the black
glassy rock called obsidian that some prehistoric people
made into knives and arrowheads.
Another kind of rock is made out of "rock powder."
Wind and rain wear off tiny, powdery bits of rock
from mountains. Rivers carry the powdered rock to
the sea, where it sinks to the bottom. Over thousands
of years, the bottom layers of powder are squeezed
together by the weight of new layers. Slowly, the

powdery bits on the bottom are turned into a layer of

solid rock. Over millions of years, earthquakes and
other forces may lift up the layers of new rock and
they become dry land.
Rocks that are made this way are called sedimentary
rocks. Sedimentary comes from the word sediment,
which means "to settle." Limestone and sandstone are
sedimentary rocks.
There is also rock that is changed deep in the earth.
62

granite — an igneous rock

The heat and weight of the earth slowly change it into

a different kind of rock. Rocks changed this way are
called metamorphic rocks. Metamorphic means
"changed."
Slate, a gray-black rock from which blackboards used
to be made, is a metamorphic rock that was changed
from clay. Marble is a metamorphic rock that was
changed from limestone. Most metamorphic rocks are
very old. They stay buried unless erosion, an
earthquake, or the birth of a mountain lifts them to
the earth's surface.
In fact, all the rocks we see were made long, long

ago. The oldest rocks ever found on earth are more

than three billion years old. But the earth hasn't
stopped making rocks — it's making them right now. It
takes a long, long time to make a rock.
Rocks, Stones, and Petrified Bones I 63

sandstone —a sedimentary rock

marble —a metamorphic rock

 Rocks, Stones, and Petrified Bones I 65

Solid stuff

It takes a lot of things to make cookies — flour, milk,

eggs, butter, sugar. But when the cookies are baked,

you can't see that there are a lot of things in them.
Everything is all mixed together.
A rock is like a cooky. Mixed into most rocks are
things that you can't see. Rocks are mixtures of
materials called minerals.
Minerals are the solid stuff that the earth is made
of. There are about two thousand different kinds of

minerals. Some are shiny, some are sparkly, some are

dull. Some are hard enough to scratch glass. Others
are so soft you can scratch them with your fingernail.

There are minerals that look like chunks of ice,

minerals that look like clusters of metal cubes, and

minerals that look like bunches of fuzzy string or
shiny hair.
Minerals are scattered throughout the earth's rocky
crust. Many of them are mixed together, but many are
by themselves, in huge chunks, little lumps, and broad
patches between layers of rock.

minerals

Minerals are the solid material of which the earth

is made. There are about two thousand different

kinds of minerals. Shown here (clockwise,

from the lower left) are: fluorite, azurite,

malachite, selenite, and, in the center, wulfenite.

66 I Rocks, Stones, and Petrified Bones

Flatsides and
sharp corners
A chunk of mineral may seem to be just a jagged,

lumpy, or twisty piece of hard stuff with no special

shape. But each kind of mineral is actually made up
of tiny shapes called crystals — shapes that have flat

sides and sharp corners, such as cubes, squares, and

pyramids.
Each kind of mineral is made up of crystals that
have the same shape. The mineral halite, which is the
salt we put on food, is made up of crystals shaped like

cubes. Diamonds are made up of crystals shaped like

pyramids. Graphite, which is the "lead" in pencils, is

made up of square crystals.

It seems strange to think of hard, lifeless things
growing. But crystals actually do grow. They don't
grow from the inside, as living things do, however.
They grow by joining together. For example, the walls
of a cave may be covered with a particular mineral.
Water trickling down the walls washes crystals of this
mineral onto the cave floor. The water, filled with
many tiny crystals, forms a puddle on the floor. As the
puddle slowly dries up, the crystals stick together.
They form larger crystals. That's how crystals grow
when more and more of them join together.
Some minerals have the same shape as the crystals
they are made of. Diamonds usually look like two
pyramids with their bottoms stuck together. Graphite
comes in flat sheets. Pyrite comes in clusters of shiny,

golden cubes. Quartz is often found in clusters of

six-sided, pointed shapes.
calcite crystals on a cave wall,
South Dakota

quartz crystals in a cave, Arkansas

1
'^

Ti/fcy
A crystal garden
When small crystals of a mineral join together, they
"grow" into larger crystals. You can see how crystals
grow by growing some crystals yourself. Here's what
you will need:

6 tablespoons of water
1 tablespoon of ammonia
6 teaspoons of salt
6 pieces of charcoal — the kind
used for outdoor cooking

Mix the water, ammonia, and

together in a measuring cup
small bowl.
 I 'ut the charcoal in a pie pan.
Pour the liquid over the pieces of
charcoal. Put the pan in a warm
place where the water will

evaporate quickly.
When the water has
evaporated, you will find you
have grown a fantastic "garden"
of crystals.

crystals grown in a dish

You can also grow crystals with nothing more than

salt and water. Table salt is a mineral called halite that
forms in cube-shaped crystals.
Put a little hot water into a small pie pan or a saucer.
Then add several spoonfuls of salt to the water. Stir the
water until all the salt dissolves. Put the pan in a place

where it will not be moved. Leave it there for a few

clays.

Slowly, the water will dry up. On the bottom of the

pan you will see a lot of shiny, cube-shaped crystals of

salt.
ancient copper head from Iran

This copper head was made thousands

of years ago. It is no longer bright
because, in time, copper is covered
with a greenish coating called patina.

Courtesy Metropolitan Museum

of Art, New York.
72

Those people of long ago found great lumps of pure

copper in the earth. But people have taken copper
out of the ground for thousands of years. Now there is

very little pure copper left. Today, most of the copper

we find is mixed with other minerals. Minerals that
contain copper are called copper ores.
Copper is an important metal. Most of the wires

that carry electricity into our houses and factories are

made of copper. This is because electricity moves
better through copper than through any other common
metal.
Tin is another metal that people have used for a
long time. It is a bluish-white metal that is heavy
and soft, like copper. It comes from a brownish, glassy,
mineral called cassiterite. People of long ago often
found pebbles of cassiterite in riverbeds. Today, most
cassiterite has to be dug out of the earth.
About five thousand years ago, ancient people
learned how to mix tin with copper. By melting tin and
copper together, they could make a metal called
bronze. Bronze much stronger and tougher than
is

either tin or copper. From bronze, the ancient people

made swords, helmets, armor, cups, bowls, and many
other things. When people learned to make bronze, it
was the end of the Stone Age and the beginning of the

Bronze Age.
When we we usually think of tin cans.
think of tin,

But tin cans are really made of iron or steel covered

with a thin coating of tin. The tin gives the cans a
shiny look and keeps the iron or steel from rusting.
 Rocks, Stones, and Petrified Bones |
73

tin ore (cassiterite)

ancient Chinese
bronze sword
74 I Rocks, Stones, and Petrified Bones

The Iron Age mineral

Safety pins and skyscrapers, scissors and steamships,

automobiles and airplanes — none of these things could
be made without the mineral called iron.

Iron is a metal, like copper and tin and bronze.

But iron is much harder and tougher. It is the best
kind of metal for making tools and things that need
lots of strength.

There is iron almost everywhere in the earth's crust,

but it is almost always locked inside other minerals.
Minerals that contain iron are called iron ores. When
these ores are heated, the iron flows out as a thick
liquid. When the iron cools, it is a hard, dull-looking
black metal.
Iron has always been an important metal since
people first began using it, about four thousand years
ago. It made better, longer-lasting tools and weapons
than either stone or bronze. The use of iron brought
the Bronze Age to an end. When people began making
things out of iron, it was the start of the Iron Age.
Many things, such as fire hydrants, fancy fences, and
parts of automobile engines are still made from iron.

But much of the iron now taken from the earth is

mixed with other materials to make an even harder,
tougher metal called steel.

People have known for a long time how to make

steel, but it was always very expensive. It was only a
little more than a hundred years ago that we learned
how to make lots of steel cheaply. So many things are
—
now made out of steel such as safety pins, scissors,

skyscrapers, and automobiles — that it is sometimes said

that we live in the Steel Age.
 Japanese iron helmet and face mask

This mask and helmet were part

of the armor of a Japanese
warrior two hundred years ago.

iron ore (hematite)

76 |
Rocks, Stones, and Petrified Bones

The Atomic Age mineral

The prospector moved slowly across a rocky, desert

hillside. He was searching for a very valuable mineral.
But he had no pick or shovel. As he walked along, he
held a metal tube over the rocks. A wire connected the
tube to a metal box he carried in his other hand.
Suddenly, a popping noise came from the box. Then
another. Then the pops came so rapidly they sounded
like a machine gun. The prospector let out a whoop of
joy. He had found the mineral —uranium.
Uranium is a mineral that is the main source of
atomic energy. It is a metal that is radioactive. This
means that, in a way, it is "exploding" — that it shoots
out tiny bits of itself in all directions. These tiny bits

are parts of the atoms of which uranium is made.

They are so small they cannot be seen with even the
most powerful microscope. But they can be discovered
by a machine called a Geiger counter.

It's a Fact
Uranium is a radioactive metal.
This means that it is constantly
"exploding," or shooting tiny bits
of itself out in all directions.
 The technician is loading
uranium fuel into rods

that will be used in a

nuclear power plant.

pieces of uranium

uranium ore
(pitchblende)
Uranium is never found by itself. It is always mixed
with other minerals. Prospectors usually look for it

in a mineral called pitchblende. Pitchblende is a lumpy

black rock that shines like fresh tar. It is found near
the top of the ground. Uranium is also found in a
powdery, yellowish mineral called carnotite that forms
in a thick coat on sandstone and other rocks.
When uranium is taken out of pitchblende or
carnotite, it is a heavy, silver-gray metal. Copper is

the metal of the Bronze Age, and iron is the metal of

the Iron Age and Steel Age, but uranium is the metal
of —
the Atomic Age which has just begun.
 ft*-;

'.**y

mercury ore (cinnabar) and mercury

 rev*
Rocks, Stones, and Petrified Bones 79

The dry liquid

Imagine a dry liquid —a liquid you can stick your

finger into without getting it wet.
There is such a liquid. It's a melted metal that stays
melted even when it's cool! No other metal does such a
thing.
This strange, liquid metal is called mercury. It comes
from a sparkly red rock called cinnabar that is found

near hot springs and volcanoes. If you ever had your

temperature taken with a fever thermometer, you have
seen one way that mercury is used. The silvery stuff

inside the thermometer is mercury. Dentists also use

mercury, mixed with silver, to fill cavities in teeth.
,

Mercury is full of surprises. When a little of it is

poured onto a slanting surface, the mercury doesn't

trickle down in a stream, as other liquids do. The
puddle stays together and just slides downhill! Given a
push, the puddle breaks into hundreds of tiny globs
that roll like little balls. And if the globs are all pushed
together, they form a puddle again.
Mercury was named after the Roman god Mercury,
who was the swift messenger of the gods. But because
mercury moves and quivers as if it were alive, it is
mercury in a
sometimes called quicksilver, which means live silver.
thermometer
Mercury is a dangerous poison. It's dangerous to
handle because it might get into your mouth and cause
sickness. Factories sometimes clump wastes containing
mercury into lakes and streams. The mercury then
gets into the bodies of fish. If people eat the fish, they
may get very sick or even die.
80

The stone that burns

"I smell brimstone! The Devil must be near!"
Long what someone might have said
ago, that's if

they smelled sulfur burning. Sulfur was called

brimstone, which means "the stone that burns."
Because it burned, and came from deep inside the
earth, people once thought it had something to do with
the Devil.
Sulfur is one of the most common of all minerals. It

is often found aboveground, near volcanoes that have

thrown it out while erupting. But it is usually found
deep underground, mixed with rock. Sulfur looks like

little chunks of bright, yellow glass. It burns with a

blue flame and gives off a smell like rotten eggs.
Hundreds of years ago, people discovered how to
make gunpowder by mixing sulfur with charcoal and
another mineral called saltpeter. As time went on,
sulfur became used for more and more things. Today,
it is used to make medicines, tires, and many other
things people use every day.
 Rocks, Stones, and Petrified Bones |
81

k*^"

sulfur
 U• i

£» Z0* '

*?.*% >>

^^^^^tjjjl
 Rocks, Stones, and Petrified Bones I 83

Precious stones

They shine, they sparkle, they flash and shimmer.

The crowns of kings and emperors were covered with
them, and wealthy people have always worn necklaces,
rings, and other jewelry made of them. They are only

stones,but they are so beautiful and hard to find that

they have been symbols of wealth and power for
thousands of years. They are the "precious stones"-
diamonds, rubies, emeralds, sapphires, and opals.
Diamonds come from deep in the earth. They are

buried in rock that is in or near dead volcanoes. Most

diamonds are shaped like two pyramids with their

bottoms stuck together. When they are taken from the

ground they are dull and grayish. It is only after they
are cut and polished that they sparkle and flash.
A diamond is the hardest of all things that come
from the earth. It can even cut rocks. The only thing
that will scratch a diamond is another diamond. Most
diamonds are used to make cutting and grinding tools.
Only the biggest, most perfect diamonds become jewels.
Corundum is a stone that's like a cube with two
corners cut off, so that it has six flat sides plus a top

and bottom, instead of four sides. It is a very common

mineral that is usually found stuck in other kinds of
rock. But sometimes a piece of corundum has a tiny bit

of another mineral, either titanium or cobalt, mixed in

jeweled crown of the Holy Roman Empire

 polished opal

%4.<

natural opal
it —and then it is a clear, blue stone called a sapphire.
And, sometimes a tiny bit of a mineral called chromium
is mixed into a piece of corundum. That makes it a
dark red ruby.
Beryl is a rock that has eight or more flat sides. It is

usually found in large chunks of granite or, sometimes,

limestone. When a tiny bit of chromium is mixed into
a piece of beryl, it makes a beautiful, deep-green stone

called an emerald.
One of the most beautiful of all precious stones is

mostly just a mixture of sand, water, and the gas

ut and polished ruby called oxygen. This stone, the opal, is often found in
large patches near the top of the earth's crust. Opals
come in all colors of the rainbow, plus black and
brown. When they are cut and polished, they sparkle
with many colors and glow as if there is fire locked
inside them.

natural sapphire

natural ruby
"C

cut and polished sapphire

 Rocks, Stones, and Petrified Bones |
N;">

The size of a diamond is

measured by its weight in
carats. This one-carat
diamond is shown actual

size, compared to a penny.

natural emerald

cut and polished emerald

cut and polished diamond

Precious stones are called gemstones. Diamonds,

emeralds, rubies, sapphires, and opals are the most
precious gemstones, but there are others. The natural diamond

gemstone called a cat's-eye is a beautiful, rich brown

with a golden stripe running through it. Jade is usually
a deep, glossy green or milky white. Zircon is a
flashing, brilliant gemstone that may be pale red,
brown, green, violet, or colorless, like a diamond.
Turquoise is bright sky-blue or blue-green. These, and
many other mixtures of minerals that are gemstones,
are used in jewelry and beautiful works of art.
86

The money minerals

Gold is a bright-yellow metal that
looks like sunlight turned to stone. Silver
is a pale-gray metal that looks like

frozen moonlight. These two minerals

are so beautiful and hard to find that
people have used them for jewelry and
for money for thousands of years.
Gold is found in many places. Usually
it is mixed in with other minerals. But
gold
big nuggets and tiny grains of gold have
been found They are brought
in rivers.

there when streams wash them out of

rocks in the mountains. Pieces of gold

S^ have also been found lying on top

ground. But most gold is now dug out
of the

of

mines.
Gold is heavy, but it is so soft it can
be hammered into sheets thinner than

silver
tissue paper. Several minerals look so

much like gold that people are often

fooled by them. But these other minerals
are usually much harder than gold.

They cannot be scratched as easily.

Silver is also found in the earth.
Chunks of silver often look like bunches
of twisted wire or feathers. Silver is not

shiny like gold — it is dull gray or black

until it is polished. It, too, is very heavy
and soft. When gold or silver ismade into
jewelry, other metals are added to make
the gold or silver hard.
 Rocks, Stones, and Petrified Bones 87

gold and silver coins

A slippery mineral

What is inside the pencil you use to write? It's often

called "lead" — but it's not really lead at all. It's a

mixture of clay and a soft, black mineral called graphite
(GRAF yt). Some graphite is found in the earth, and
some graphite is manufactured.
Graphite is not found in hard, many-sided crystals, as
some other minerals are. Instead, made up of flat
it is

layers that easily slide over each other. This makes

graphite soft and. slippery. When graphite is used in

pencils, it slides easily over the paper and leaves a black

mark.
Graphite is so slippery that it can sometimes be used
in place of oil. People use graphite to "oil" locks, clocks,

and all sorts of small machines. And in cold weather,

when oil turns thick and hard, graphite stays soft and
slippery. In winter, and in cold places, it often works
better than oil.

The container that holds

white-hot, melted steel is

made of a material that

contains graphite.

graphite in pencil lead

 Rocks, Stones, and Petrified Bones |
ISO

Graphite can be used in other special ways. It does not

melt easily, so it is often used to make pots for melting
metals. It does not dissolve easily, so it is often used in
making tanks that hold strong chemicals.
And, even though a slippery, soft piece of graphite and
a hard, sparkling diamond don't look much alike, they
are both made of the same kind of material. So graphite
is used to make artificial diamonds for cutting and

grinding. The diamonds made from graphite work as

well as real diamonds do.

a steel foundry

mlt
)
9.
«'

j*-
 Rocks, Stones, and Petrified Bones 91

Buried sunshine

Nearly all rocks are made of minerals — things that

are not alive and never have been. But there is one
kind of rock that is not made of minerals. It is coal, a

black shiny rock made of — green plants!

Millions of years ago much of the world was hot and
swampy. Strange-looking trees and giant ferns covered
most of the land. When these big plants died, they
toppled over and sank into the mud. Then they were
buried under other plants that fell on top of them. In
time, there was a thick layer of dead plants. As the
plants rotted, they formed a thick, lumpy brown stuff

called peat.

Parts of the land began to sink. Water poured in,

bringing mud and sand that covered the peat. Tons of

water, mud, and sand pressed down on the peat,
squeezing it tightly together. All this weight and
squeezing turned the peat into coal.
After millions of years, the earth changed. Places
that had been covered with water became dry land.
Mud and sand had turned to rock. The great masses of
coal were buried deep in the rock.
Today, miners dig coal out of the earth. Coal is

burned to heat houses, schools, and other buildings.

Burning coal is used to make steam that turns the big
machines that make electricity for heat, light, and
power. When we burn coal, we are really burning
plants that grew millions of years ago. This is why
coal is sometimes called "buried sunshine."
92

Black gold

The oil that keeps your bicycle from squeaking and

the gasoline that keeps your parents' car running both
come from deep in the earth's crust. Both began as a
thick black liquid found in big pools between layers
of rock.
Oil is not a mineral. Like coal, it was made from
things that were once alive. Oil is found in places

where there were seas and oceans millions of years ago.

Tiny plants and animals lived along the shores of these

seas, just as they do today. When these creatures died,

their bodies drifted down to the sea bottom. Over
millions of years, billions of these tiny dead creatures
formed deep piles.

Sand and mud settled over the piles of dead

creatures and formed thick layers. Slowly, these layers
were squeezed together by their own weight and the
weight of the water pressing down on them. They were
squeezed so hard they became layers of rock.
Scientists think that the heat and weight of the rock,

pressing on the piles of dead, rotting plants and

animals, turned them into drops of oil.

Today, people drill down through many layers of

rock to find pools of oil. From oil we get gasoline to

run the engines of cars, trucks, and tractors. Many

kinds of plastics and other things are made from oil.

And it is used to heat houses, factories, and schools.

Because oil was first found seeping up between rocks,
it —
was called petroleum from two Latin words
meaning "rock oil." Today, petroleum is usually just
called oil. But it is so important, and worth so much,
it has been nicknamed "black gold."
Rocks, Stones, and Petrified Bones I 93

crude and refined oil

Crude oil, or petroleum, is

often called "black gold."

This is because the valuable
crude oil is thick and black
when it comes out of the
ground. It is then sent to
a refinery to be made into

fuel oil, gasoline, kerosene,

and other products.
 i

table salt (halite crystals), magnified

1
 Rocks, Stones, and Petrified Bones |
95

A rock we eat!

If someone at the dinner table said, "Pass the rocks,

please," what would you give that person?

Salt, of course!

The salt that people use to season food is a mineral

called halite. Big lumps of halite are found in the
earth's crust. The halite is dug out in chunks and
crushed up small enough to fit through the holes in a

saltshaker. Halite forms in square crystals. No matter

how small it is crushed, it nearly always breaks into
the shape of a cube.
Sometimes, a hole is dug down to salt that is in the
earth.Water is forced down into the salt, then pumped
back up with salt in it. The water is then heated.
When it dries up, crystals of pure salt are left. Salt is

removed from seawater in much the same way.

People need some salt to keep healthy, and many
people think salt makes food taste better. So salt has
always been very important to people. In ancient
times, salt was so precious and hard to get that was it

used as money. The soldiers of ancient Rome were

given salt as pail of their pay. This part of their pay
was called the salarium. Our word salary, which is

another word for pay, comes from the Latin word

salarium. A man who was not a very good soldier was
"not worth his salt." We still say this about people who
don't do a good job for the money they are paid.
96

aluminum ore (bauxite)

The "magic" metal

Have you ever watched someone wrap a sandwich
or cover a bowl of food with what looks like a sheet of
shining, silver paper? It isn't paper at all — it's a thin
sheet of the wonderful metal called aluminum.
Aluminum is a light, silvery metal. It is never found
all by itself, as a pure metal. It is always mixed with

other minerals. Most aluminum comes from a rock

that looks like a bunch of brown pebbles mixed into a
piece of gray concrete. This rock is called bauxite.

Aluminum is often called the "magic" metal. It is

light, very strong, and won't rust. It can be stretched

and any shape. So aluminum is used
rolled into almost

to make everything from airplanes to pots and pans

to chewing-gum wrappers.
This metal has two names. People in the United
States call aluminum (uh loo muh nuhm). But people
it

in Great Britain, Canada, Australia, and many other

countries call it aluminium (al yuh mihn ee uhm).

 Rocks, Stones, and Petrified Bones |
97

a roll of sheet aluminum

98 Rocks, Stones, and Petrified Bones

Bones in rock

A giant dinosaur, with jaws shaped like the bill of a

duck, plodded along the shore of a lake in search of
food. Sighting large horsetail plants growing in shallow
water, it waded out toward them.
Suddenly, the big dinosaur stepped into a wide, deep
hole filled with soft, watery mud. At once, the animal
began to sink.

It thrashed about wildly, trying to find solid ground

under its feet. The weight of its own body dragged it

down. The mud rose to its chest, then to its neck.

Slowly, its head went under. Mud filled its mouth and
nostrils and it died. That was eighty million years ago.
The dinosaur's body sank to the bottom of the hole.

Slowly, the soft parts of the dinosaur rotted away.

Only its bones were left.

Over many years, the mud around the bones was

packed tightly together. In time, it became clay. Over
many more years, the clay turned to rock. And, as still

more years passed, the lake dried up. The rock with
the dinosaur bones in it was now the side of a cliff.

During all those years, water filled with dissolved

minerals often got into the bones. Slowly, all the
100 I Rocks, Stones, and Petrified Bones

hollow places in the bones were filled with dissolved

minerals that then hardened.
As millions of years passed, wind and rain slowly
wore away the side of the cliff. Finally, so much rock
was worn away that some of the dinosaur bones,

preserved in the rock all those years, were sticking out.

One day, eighty million years after the dinosaur had
died, a group of scientists saw the bones sticking out
of the cliff. With pickaxes and crowbars, the scientists

removed the bones from the rock.

The scientists packed the bones carefully and sent
them to a museum. At the museum, the bones were put
together. People could then see the skeleton of the
giant creature that had lived so long ago.
Most of the skeletons of prehistoric animals that
you see in museums were preserved in rock in this way.
Such preserved bones are called fossils. Sometimes, all

of the original material is replaced with minerals. Then

the fossil is said to be petrified, or turned to stone.

Its a Fact

Trees have been preserved

just as dinosaur bones were.
In Arizona, there's a petrified
"forest" of tree trunks that
were turned to stone millions

of years ago.
taking fossil bones from rock
102 I Rocks, Stones, and Petrified Bones

Pictures in stone

Tucked away in the earth's rocks there are often

"pictures" from the past.

Many times, in ages past, animals walked through
mud and left footprints. Slowly, over thousands of
years, the mud hardened into rock. The footprints
were preserved forever. We have found rocks in which
there are footprints of dinosaurs and other animals.
We have even found rocks with the footprints of

prehistoric people.
Leaves of ancient plants and feathers from the first

kinds of birds also fell into the mud. They, too, left

prints that were preserved when the mud hardened

into rock.
Ancient snails, clams, and other shelled sea creatures

died and were covered up with mud. The mud ^ *

hardened around them. When their soft parts rotted

away, and their shells dissolved, a hole was left in the

rock —a hole the exact shape of the dead animal. This
hole was like a mold. Slowly, it filled up with minerals
that hardened into stone. The stone was the exact
shape the dead animal had been.
These pictures and shapes in stone are called fossils.

They tell us about the plants and animals of millions

of years ago.
k
/

m
 Rocks, Stones, and Petrified Bones |
105

Layer cakes of rock

The upper part of the earth's rocky crust is like a
layer cake. It is made up of many layers of different
kinds of rock, one on top of the other. These layers
were built up slowly, one after the other. Here is how
this might have happened in one place.
At first, there was only the top of the bare rock
crust. Volcanoes erupted, pouring out ash and lava that
hardened into a layer of black rock called basalt.

Earthquakes caused this part of the land to sink.

Ocean water flowed in to form a smaller body of water

called a sea. Rivers dumped tons of sand into the sea
for thousands of years. The sand sank down and

formed a thick layer on top of the basalt.

Snails, clams, and other little shelled animals moved

in from the ocean to live in the sea. When they died,
their bodies sank down onto the sand. Their soft parts
rotted away and only the shells were left. For millions
of years, these shells piled up until they formed a
thick layer.
The weight of the shells and the water squeezed the
sand together until it became a layer of the rock called

sandstone. Squeezed together by their own weight and

the weight of the water, the shells were crushed into
powder. Minerals in the water glued the powder
together. After millions of years, the powdered shells

were a layer of the kind of rock called limestone. The

layer of limestone was on top of the layer of sandstone,

which was on top of the layer of basalt.

This kind of building up of layers of rock is still

going on. The layer of mud that now lies at the bottom
of a sea will some day be a layer of rock!
entrance to Russell Cave, Alabama
 Rocks, Stones, and Petrified Bones I 107

Holes in rock

A den for bears and a bedroom for bats. A home for

prehistoric people. A dark place of gloom and mystery.

A sparkling wonderland of strangely shaped rocks.
That's a cave!
A cave is simply a hole in the earth. It may be a
small hole, not much bigger than a room in a house. It
may be a place of long, twisting tunnels and huge
caverns. It may be high up on a mountainside or it

may be in the ground.

Most caves are in the kind of rock called limestone.
These limestone caves are made by water. Water seeps
through cracks in the rock. It trickles downward,
carrying dissolved limestone with it. Slowly, the
cracks grow wider as more and more limestone is

carried away. After many thousands of years a cave

may have a great many winding passages and broad
rooms, all made by the slow trickle of water.

underground water
in a cave
108 I Rocks, Stones, and Petrified Bones

Stone icicles

Many a cave is filled with what look like giant

stone icicles. Some of these "icicles" hang down from
the cave's roof. Others stick up from the floor. They
are often as thick as tree trunks. Sometimes, the ones
on the ceiling and the ones on the floor meet to form
thick pillars. These strange-looking stone "icicles"
are usually found in limestone caves.
The "icicles" that hang from the ceiling are called

stalactites. They made by water trickling through

are
cracks in a cave's limestone roof. The water carries
tiny bits of the mineral called calcite with it. As some
of the water dries, it leaves bits of calcite stuck to the
ceiling. Each drop of water adds more calcite. Slowly,

as more bits of calcite are added, the stalactite grows

longer and longer.
Some of the water drips to the cave floor. This water
also has bits of calcite in it. As the water dries up,

bits of calcite are left on the floor. Slowly, the calcite

piles grow higher and higher. These "icicles" sticking

up from the floor of a cave are called stalagmites.

Often, water drips off a stalactite onto the top of
a stalagmite below it. Slowly, the two grow toward one
another until they finally join.

Many people get stalactites and stalagmites mixed

up. They remember which hangs from the ceiling
can't
and which sticks up from the ground. But there is an
easy way to remember. Just remember that ceiling
begins with c, and stalactite has a c in it. And ground
begins with g, and stalagmite has a g in it. Then you'll

always know that stalactites hang from the ceiling and

stalagmites stick up from the ground.
 water droplets on stalactites

Stalactites and stalagmites,

Carlsbad Caverns, New Mexico
/
 Ill

Oceans,
Lakes,
and Rivers

r^y>\
The deep blue sea

The sea! the sea! the open sea!

The blue, the fresh, the ever free!

Without a mark, without a bound,

It runneth the earth's wide regions round.

From The Sea

Barry Cornwall

Sailors talk about "the seven seas," but there is

really only one big ocean. The lands we live on, even
 Pacific

North Pole

Atlantic

Atlantic

Pacific

South Pole

Indian

It's a Fact

There is really only one big ocean.

It covers about three-fourths of the
earth. You can see this clearly if you
look at a globe from the top and bottom.

giant continents such as North and South America,

are really just islands in this huge ocean.
Large parts of this one big ocean lie between the
continents. These parts have different names. The
biggest part is called the Pacific Ocean. The next
biggest part is called the Atlantic Ocean. There is

also the Indian Ocean near India, the Arctic Ocean

around the North Pole, and the Antarctic Ocean near
the South Pole.
Smaller parts of the ocean, near islands or between
pieces of land, are sometimes called seas. But we also

call the whole ocean a sea — the deep, blue sea.

 ,p "Iwf

114 I Oceans, Lakes, and Rivers

Where did the

ocean come from?
Scientists tell us that billions of years ago the earth
was a ball of bare, sizzling-hot rock, with no air or

water on it. The outside of the earth slowly cooled,

but the inside stayed fiercely hot. Volcanoes roared
and rumbled, throwing out tons of melted rock and
enormous clouds of hot gases. One of these gases was
steam —water so hot it is gas. When steam cools it

turns into water.

Some scientists think the steam rose up in clouds.

When these clouds cooled, they became water that fell

as rain. Slowly, the low parts of the earth's rocky crust

filled up with water, forming the ocean.
Other scientists think the steam cooled as it came
out of the earth. When it became water, it trickled
downhill. During many millions of years, the low places
filled up to form the ocean.
Whichever way it happened, the ocean was formed
by steam from inside the earth — steam that cooled and
became water.
spins
***** *^*-\ ^£ . «/ /
The bounding waves
Stand at the seashore, or a lakeside, on a windy day.
Watch the waves as they rush in toward you. They seem
to come rolling at you as if pushed by a giant hand. With
a great hiss and a swirl of foam, they surge up onto the
beach. Then, almost at once, the water flows back out
again. Only a last few sparkles are left on the wet sand.
Waves are made by wind blowing along the top of the
water. The water seems to be moving forward but it —
really isn't! It only moves up and down. A cork floating

on the water would bob up and down as a wave moved

under it. Unless pushed by the wind or tide, it would
stay in the same place. This is because the water in a
wave does not move forward. Only the shape of the
wave moves forward.
You can see this for yourself. Tie a length of rope to a
tree or post. Then wiggle the loose end of the rope.
You'll see a wave shape travel down the rope. But the
rope stays in the same place.
When a wave reaches land it "breaks." The bottom of
the wave drags on the ground where the water is
shallow. The top keeps going. It spills up onto the beach,
then slides back again.

T»* M«
I^B^Ull:
high tide

low tide
 Oceans, Lakes, and Rivers 119

High tide, low tide

It is early in the misty morning. You are standing

on a cliff that overlooks the sea. Gulls soar overhead,
calling to one another with shrill cries. Below you, the
gray sea crashes against the shore. You can see a wide
stretch of rocky beach sloping down to the water.
But if you come back to the same place six hours
later, everything will be different! Now, at noon, the

sea has risen. The beach has disappeared and the water
is lapping against the side of the cliff. And if you come

back in six more hours, things will have changed again.

You will see the beach, and the sea will be low again.
This rise and fall of the sea is called the tide. Tides

are caused by the earth's spin, and by gravitation, the

mysterious force that makes things tug at each other.
In this case, it is mostly the gravity of the moon
tugging at the earth. High tides take place on the part
of the earth that is nearest to the moon. The moon's
gravity pulls the water slightly away from the earth.

At the same time it is also high tide on the opposite

side of the world. There, the tug of the moon's gravity
is weaker, and the force of the earth's spin pushes the
water outward.
As the earth turns, the part of the sea that is high
moves away from the moon's gravity. The water sinks
back down. After about six hours, this part of the sea
is all the way down to what is called low tide.
Each part of the sea has two high tides each day
one when it is beneath the moon and one when the
moon is on the opposite side of the earth. And, of
course, there are also two low tides each day.
120

The bottom of the sea

What lies beneath the ocean? What's at the bottom
of the deep blue sea?
Tall mountains! Great plains! Deep valleys!

Volcanoes
The whole outside of the earth is covered with a
rocky crust. The continents and islands, the parts on
which we live, are the highest parts of the crust. The
lowest parts are covered by the seas and oceans. So the

'

V.
 Oceans, Lakes, and Rivers 121

bottom of the sea is really part of the earth's rocky

crust. It is much like the part we live on.

There is a great mountain range that runs clown the

middle of the Atlantic Ocean. It is longer than any
mountain range on land. The tops of some of the
mountains stick up out of the water, forming islands.

The deepest parts of the ocean are long, narrow

valleys called trenches. The very deepest of these,

called the Mariana Trench, is in the Pacific Ocean.

There, the bottom of the trench is 36,198 feet (11,033
meters) below the surface of the water.

"V>
an iceberg near Antarctica

Floating mountains of ice

What is that great, shining shape floating in the cold,

gray water of the northern sea? Is it a mountain of
snow? Is it an island of ice where the Frost Giants live?

Is it the great, cold castle of the Snow King?

No, it's none of these things. It's an iceberg — one
of the enormous chunks of ice that float in the ocean
near the North and South poles. An iceberg can be as
big as a mountain, as wide as an island, and as
beautifully shaped as a castle. Many icebergs weigh
millions of tonsand are many miles (kilometers) wide.
Giant sheets of ice cover the South Pole and a large
 Oceans, Lakes, and Rivers I 123

part of Greenland, near the North Pole. Icebergs are

huge pieces that break off from the edges of these ice

sheets.The bergs drift along in the ocean until they

reach warmer water. Then they begin to melt and
break apart. In time, they melt completely and become
part of the ocean's water.
An iceberg may stick far up out of the water. It may
tower over great ships and make them look like toy
boats. But the part above the water is only a tiny bit
of the whole iceberg. The part below the surface may
be six times bigger than the part we see.

1
124 I Oceans, Lakes, and Rivers

rocky beach
sandy beach

Where the sea

meets the land
Wherever the sea touches land, whether it's the edge
of a tiny island or the coast of a continent, there is

almost always a beach.

A beach is a stretch of sand, pebbles, or mud. The
sea makes beaches. Waves, crashing into a rocky shore
for thousands of years, toss the rocks around, breaking
them into pebbles. Then, for hundreds or thousands of
years more, the waves grind the pebbles together. In
time, the pebbles are ground into tiny grains of sand.
Lakeshore beaches are also formed in this way.
Where a river flows into the sea, a beach is usually
made of mud. That's because the river carries mud
along with it. The river dumps the mud at the edge of
the sea, where it piles up and makes a beach.
 mm
*c

*>
M wi

bay, Isle of Man

Where the sea

pokes into the land

A bay is a place where a tiny bit of the sea, or a

lake, pokes into the land. Seen from an airplane, a bay
often looks as if a giant had taken a big bite out of the
edge of the land and water had come in to fill the hole.
An inlet is also a body of water that pokes into the
land. But an inlet is long and narrow — more like a
finger than a bite.
 Oceans, Lakes, and Rivers 127

Why the sea is salty

You could be out in the middle of the
ocean — surrounded by thousands of miles
(kilometers) of water— and not have a
drop of water you could drink. For
seawater is full of salt. If you did drink
it, it would simply make you more thirsty.

The sea is salty because rivers dump

salt into it. All the rivers that flow down
mountainsides and over the land tear
loose tons and tons of minerals. Most of

these minerals are different kinds of salts.

The rivers carry these salts to the sea.
There's never enough salt in a river to
make the river water taste salty. But
rivers have been dumping salt into the
sea for millions of years. By now, there is

enough salt in the sea to cover all the

land on earth with a layer of salt
hundreds of feet (meters) deep!

harvesting salt from the sea, Colombia

These cone-shaped mounds are piles

of salt. As the seawater evaporates,

the salt that remains is raked into
piles and left to dry in the sun.
128 I Oceans, Lakes, and Rivers

The story of a river

A river may begin as a trickle of melting snow, high

on a mountaintop. It may begin as a trickle of
underground water, bubbling out from under a rock on
a mountainside.
The trickle winds down the mountainside, following
the easiest path in and out among the rocks. It is so
narrow you could step across it. Farther down the
mountainside, it is joined by another little trickle. The
two of them move along together, forming a wider,
faster-moving stream.

narrow mountain stream, Italy

mountain stream, Poland

Soil and stones, carried along by the rushing water

day after day, year after year, cut a groove into the
mountainside. The bottom of this groove is the bed of
the stream. And the high sides of the groove are its

banks.
130

One after another, more trickles join the stream and

it grows wider. Now it is a river, fast and wide, rushing
down the sloping mountainside.
In one very steep place, the fast-moving river has
worn away the soft rock. Only bumps of hard rock are
left. These rocks stick up out of the riverbed. The

river swirls and foams around them. This part of the

river is called the rapids.

rapids in Las Animas River, Colorado

 Oceans, Lakes, and Rivers I 131

waterfall in Columbia River, Washington

Not far from the rapids, the mountainside ends in a

cliff. The rushing river hurries to the edge of the cliff

and falls hundreds of feet (meters) in a roaring,

tumbling, splashing waterfall.

132 I Oceans, Lakes, and Rivers

The bottom of the waterfall is near the bottom of

the mountain. The land there slopes very gently, so the

rivermoves more slowly. The river leaves the mountain
behind and flows out onto a plain. There, it moves even
more slowly, because the plain is almost level.
Other rivers from other mountains join the first

river. Together they become a great, broad river that

flows slowly across the plain on its journey to the
distant sea.

It's a Fact

The Nile is the longest river in

the world. It flows for 4,160 miles
(6,694 kilometers), from the
highlands of east-central Africa,
past the temples and pyramids of
Egypt, to the Mediterranean Sea.

if
Columbia River, near its mouth
between Washington and Oregon
134

Where a river
meets the sea
What has its head at one end and its mouth at the

other end?
A river! The place where a river begins is called its

head. And the place where it comes to an end, where it

flows into a lake or the sea, is called its mouth.

At the edge of the sea, a river's mouth is often a
sort of dumping place. As a river moves through the
land, it tears sand and soil from its banks. Rain washes
more sand and soil into it. The river carries the sand
and soil with it on its journey to the sea.
If there are no strong tides or big waves at the
river's mouth, the soil and sand sink down to the
bottom. As this soil and sand pile up in the riverbed, a
kind of island forms in the middle of the river's mouth.
Then the river has two branches that flow into the sea.

Slowly, the island gets bigger. In time, islands form

in each of the branches. These islands split the river
into still more branches. And after a long, long time,

there is a great plain at the river's mouth, with many

branches of the river running through it. This plain,
usually shaped somewhat like a triangle, is called a

delta. It gets its name from a letter of the Greek

alphabet called delta, which is shaped like a triangle.
The deltas of such rivers as the Mississippi, the Nile,
and the Amazon are hundreds of miles (kilometers)
wide. These deltas have been growing for thousands of
years. They will keep growing for many years to come.
 Oceans, Lakes, and Rivers |
135

Tongariro River Delta, New Zealand

1
Flood!

The water is rising! The river is spreading into the

streets of the town! It's a flood!
Rivers often cause floods because of too much rain or
the sudden melting of lots of ice and snow. A lot of the
rain that falls on land runs into the nearest river. Water
from melting ice and snow also runs into rivers. So,

when there is a long, heavy rain, or lots of melting ice

and snow, tons and tons of water may pour into a river.

i'i
Just as a bathtub will overflow if you keep running water
into it, the river soon spills over its banks and floods the
land.

Hurricanes and other bad storms sometimes cause

floods along the seacoast. Strong winds push great
waves far onto the land. Soon, much of the shore is

under water.

L-Ujj

&3e&
138 Oceans, Lakes, and Rivers

Holes full of water

A lake is the exact opposite of an island. An island

is a piece of land that has water all around it. A lake,

or a pond, is water that has land all around it. Some

of the places we call seas, such as the Dead Sea, are
really lakes, because there is land all around them.
Most lakes are just holes in the ground that are
filled with water. Many such holes were dug by
glaciers. Long ago, these huge rivers of ice flowed out
of the north and covered many parts of the world.
As the gigantic glaciers slid slowly along, they gouged
out great pits and made valleys wider and deeper.
Then, when the glaciers began to melt, the water filled

up many of the holes, forming lakes.

Some lakes form when part of the earth caves in,

leaving a hole. This happens mostly in places where the

ground is limestone. Year after year, rain dissolves

away the soft limestone. As the rainwater trickles

through the limestone, underground caves and tunnels

form. Finally, the tops of these tunnels cave in, leaving
what is called a sinkhole. Rain, or water from
underground springs and streams, fills the sinkhole and
it becomes a lake or pond.
Part of a river can also become a lake. Sometimes a
river deposits so much mud and sand that the water
backs up and forms a natural lake. Or, people may
make a lake by building a dam that causes the flowing
water to spread out over the river's banks.

Some lakes were once volcanoes! They formed when

the craters of dead volcanoes filled up with rain water.
 ^a
I; t.
a lake in Germany

It's a Fact

A few lakes, such as Crater

Lake in Oregon, are dead
volcanoes that have filled

up with rain water.

a spring in Arizona

spring

water table

solid rock
 Oceans, Lakes, and Rivers 141

Water beneath your feet

All the earth's water isn't in seas, lakes, ponds, and

rivers. A lot of it is beneath your feet — down in the

ground.
When rain falls, much of the water seeps down
through the soil. It keeps going until it reaches solid
rock that it can't get through. Then it spreads out,
filling every nook and cranny in the ground.
The top of this underground water is called the water
table. When there is a lot of rain, the water soon fills

all the open spaces. Then the water table gets higher.
In some places the water table comes all the way to
the top of the ground. Then, water bubbles out and
makes a natural fountain called a spring. Sometimes a
spring is the stall of a river.
Underground water is usually cool and clean and
good to drink. People often dig wells to get this water.

There is some underground water almost everywhere

in the world — even in deserts. But in a desert the

water is very, very far down.

a spring in California

':
i ih >-k *•'• L^Yf 5-» ¥1 V h£»^8

*\
hi «.
142 |
Oceans, Lakes, and Rivers

Hot-water fountains
in the earth

On a bare, rocky patch of land sits a cone-shaped

hump of rock with a hole in its top. Suddenly, with a
hiss, a great, silvery spray of steam shoots up out of
the hole. A geyser has erupted.
Geysers are the earth's hot-water fountains. Some
geysers shoot out steam every few months. Others go
off several times an hour. Some of the most famous
geysers shoot steam more than a hundred feet (30

meters) into the air.

Geysers are found in groups in several parts of the

world. They are near places where cold water from a
river or lake drains down into the ground until it

reaches hot rocks below the earth's crust. The hot

rocks turn the water into steam. The steam pushes up
through cracks in the earth and comes shooting out
into the air. Sometimes the steam cools off before it

reaches the surface. Then, hot water comes bubbling

up out of the ground.

Grotto Geyser, Wyoming

 145

Wind,
Air,

Clouds,
and Weather
146
 Air. Wind, Clouds, and Weather 141

A wrapper of air

Long ago, people believed that the sky was a shiny

metal roof stretched over the earth! Now, of course, we

know what the sky really is. It's simply air — a covering
of air around the earth. Air wrapped around the earth
is

somewhat like the skin of an orange is wrapped around

the fruit inside. This wrapper of air is called the

atmosphere (AT muh sfihr).

The atmosphere touches the ground everywhere. It is

held to the earth by the pull of the earth's gravity. Close

to the ground, where the pull of gravity is strongest, the

wrapper of air is thick. Farther away, where the pull of

gravity is not so strong, it gets thinner. Finally, many
miles from the earth's surface, the atmosphere thins out
and disappears. Where it ends, outer space begins.

earth's atmosphere

The bluish haze is the earth's

wrapper of air. The white ripples

are clouds. This photograph was

taken from the Gemini 6 spacecraft.
148

Is air something?
Air doesn't seem to be made of anything. It has no
color, taste, or smell. And you can see right through

it. But it is made of something. It is made up of

many kinds of gases. And these gases are made up of

tiny, tiny things called molecules.

Actually, everything ismade up of molecules — rocks,

plants, animals, water, and gases. The molecules in a

rock are packed close together and hardly move. The

molecules in a liquid, such as water, are farther
apart and move rather fast. But the molecules of a
gas are quite far apart and zip about rapidly. That's
why gases are so "thin" and invisible.
For us, the most important of all the gases in the
air is the one called oxygen. The only reason we
breathe is to get oxygen into our bodies. We couldn't

You can prove that air is made up of

something — that it takes up space.

Turn a glass upside down and push it

straight down into a bowl of water.

The water won't fill up the glass
because air is trapped in the glass.
 Air, Wind, Clouds, and Weather |
149

live without it. Almost every kind of animal and plant

in the world must have oxygen or it will die.

Only about one-fifth of the air is made up of

oxygen. Most of the air — nearly four-fifths of it

is a gas called nitrogen. The rest of the air is made

up of many different gases.
There is also a great deal of water vapor and bits

of dust floating in the air. But these things are

not really part of the air itself.

If air is just thin, floating gases, why doesn't it

drift away into outer space? What keeps the gases

from just floating away until they are gone?
The answer to that is gravity. Earth's gravity pulls
at all the molecules of air, just as it pulls at you.

The air can no more float off into space than you can!

Turn the glass on its side so the

air can escape. You will see bubbles
of air rush out of the glass. Now
the glass will fill up with water.
You have proved that air is made up
of something that takes up space.
 IgW^i —1

Bl I

*^^>>^
 Air, Wind, Clouds, and Weather I 151

Why is the sky blue?

I don't suppose you happen to know

Why the sky is blue? It's because the snow
Takes out the white. That leaves it clean

For the trees and grass to take out the green.

Then pears and bananas start to mellow

And bit by bit they take out the yellow.

The sunsets, of course, take out the red

And pour it into the ocean bed

Or behind the mountains in the west.

You take all that out and the rest

Couldn't be anything else but blue.

—Look for yourself. You can see it's true.

Why the Sky Is Blue

John Ciardi

This is a fun way to explain why the sky is blue,

but it isn't true, of course. The sky really gets its

color from the sunlight passing through the air.

Sunlight contains all the colors of the rainbow.

These colors are scattered as the sunlight passes
through the molecules of gas that form the air. On a
clear day, when the sun is high in the sky, blue is

scattered most of all. It is reflected into your eyes

from all parts of the sky. So, the sky looks blue.
But at sunrise and sunset, the sun appears low in

the sky. Its light passes through particles of smoke

and dust close to the ground. These particles scatter
all the colors except red and orange. So, the sun

looks like a big orange-red ball. The red and orange

reflect off the bottoms of low clouds and make the
sky look red or pink.
 Air, Wind, Clouds, and Weather |
153

Where the air came from

Scientists think the earth's atmosphere has changed
during the billions of years since the earth was formed.
At first, the atmosphere was probably very different from
what it is now. It began to change as some of the gases

went off into space.

For many millions of years the earth was fiercely hot.

Clouds of hot gases from inside the earth came out of

cracks and volcanoes. As these clouds spread out, they
became part of the atmosphere. These gases changed the
atmosphere, but, you couldn't have breathed the air. It

had no oxygen to keep you was made up mostly

alive. It

of steam, and gases called nitrogen and carbon dioxide.

But as the earth grew cooler, some of the steam
broke up into the two gases steam is made of— and one
of those gases is oxygen. So, some oxygen became part

of the air. Much of the steam became water, and

formed the first ocean.
After millions of years there were billions of tiny green
plants in the ocean. These plants, called diatoms, made
their own food out of water, sunlight, and carbon
dioxide gas, just as green plants do today. When plants
make food, they give off oxygen, so for millions of
years the little diatoms put oxygen into the air, helping
to make the kind of atmosphere we have now.
 Air can push!
You're like a fish living at the bottom of the ocean. But
X you live at the bottom of an ocean of air! Miles
(kilometers) of water are piled up above the fish, and
miles of air are piled up above you.
All that air is heavy. It has weight. The weight of the
air presses against you, even though you don't feel it.

Here's how you can tell that air is pressing on things.

You'll need:

a drinking glass (it stiff cardboard

must be glass — not your sink, or a
paper or plastic) dishpan
water

Fill the drinking glass with water to the very top. Put
the stiff cardboard over the glass. Make sure the
cardboard covers the whole top.
 Now, hold the cardboard in place
with one hand and carefully turn
the glass upside down. Do this over
a sink in case the cardboard slips.

When the glass is upside down,

take your hand off the cardboard.

You may think the water will push

the cardboard away and spill out. But
this won't happen! The air beneath the
cardboard weighs more than the water
in the glass. So the ah holds the
-

cardboard in place, because it pushes

harder against the cardboard than the
water does.
156

What makes wind blow?

The wind moves over the land. It sways the tops of
tall grass in meadows and sets leaves a-rustle in the

woods. It scatters the smoke from chimneys. It lifts

up limp flags and makes them flap. It touches your
cheek with cool, quick fingers and impishly ruffles your
hair. Wind is moving air. And it is the sun that makes
air move.

Sunlight falling upon the earth warms the ground in

many places. The heat from the ground then warms the
nearby air. As the air grows warmer, it starts to rise.
 Air, Wind, Clouds, and Weather I 157

The earth spins around like a big top. As it spins,

each part of the earth, in turn, comes into the sunlight.

The sun's light warms the earth. The heat makes the
molecules of gas in the air move faster and spread
apart. This warm air rises up, in a kind of big, invisible
cloud. As the warm air rises, cooler air from other
places flows in to replace the warm air. This moving,
cooler air is the wind. When you feel the wind blow,
you are feeling the movement of the cooler air pushing
in to take the place of the warm air.

As the warm air rises, cooler air from a cooler spot

rushes in to take its The movement of
place.
this cooler air is the wind. Wind is just moving air.
158 I Air, Wind, Clouds, and Weather

The moving air

When the air seems calm, and you can't feel a wind,
it doesn't mean that the wind has stopped blowing
everywhere. For there isn't just one wind, there are
many. In one place, there may be a soft breeze. In
another place, there may be a fierce gale. In one place,
the wind may blow from the north. In another place,
itmay blow from the south.
There may even be two different winds in the same
place! Near the ground, a wind may be pushing all the
smoke from chimneys in one direction. But up in the
sky, another wind may be making the clouds scurry in
another direction.
Earth's air is always moving. It may move only a
few feet (meters) —from a cool, shady park into a hot
street. Or, it may move great distances —from the
middle of the ocean to a place far inland. But wherever
and whenever the air moves, there will be a wind.
High above the clouds, more than five miles (8

kilometers) up in the sky, are the fastest of all winds.

These winds are called jet streams — long, narrow

currents of air that sometimes move as fast as three
hundred miles (483 kilometers) an hour.
Much of the time, jet streams are connected together.
Then they form one great, rushing river of wind that
circles the earth. This great wind moves from west to
east. When a jet airplane takes off for a long trip from
west to east, the pilot usually heads up into the jet

stream. The strong wind of the jet stream gives the

plane a powerful push. This great tail wind can
sometimes cut the regular flight time almost in half.
160

How hard is
the wind blowing?

A gentle breeze ruffles your hair. A strong breeze

may turn your umbrella inside out. On these pages
you will find out how
how hard the wind is
to tell

blowing by watching what it does. And you will learn

the names we give to different speeds of wind.

In calm air, smoke rises straight up.

The wind is blowing less than 1 mile

(1.6 kilometers) per hour.

In light air, smoke drifts slightly, but

weather vanes do not move. Wind speed is

1-3 miles (1-5 kilometers) per hour.

A light breeze moves weather vanes and

makes leaves rustle. Wind speed is

4-7 miles (6-11 kilometers) per hour.

33 A gentle breeze makes leaves and small twigs

move and light flags flutter. Wind speed is

8-12 miles (12-19 kilometers) per hour.

In a moderate breeze, small branches sway

and dust and paper blow about. Wind speed
is 13-18 miles (20-28 kilometers) per hour.

\nnni f l&y
 Air, Wind, Clouds, and Weather |
161

In a fresh breeze, small trees sway and

waves break on lakes. Wind speed is
19-24 miles (29-38 kilometers) per hour.

A strong breeze makes big branches sway

and may turn umbrellas inside out. Wind speed
is 25-31 miles (39-49 kilometers) per hour.

In a moderate gale, whole trees sway and it

is hard to walk against the wind. Wind speed

is 32-38 miles (50-61 kilometers) per hour.

A fresh gale breaks twigs off trees and

makes walking very difficult. Wind speed is

39-46 miles (62-74 kilometers) per hour.

A strong gale blows off roofs and

may do slight damage to buildings. Wind speed
is 47-54 miles (75-88 kilometers) per hour.

A whole gale will uproot trees and often

do much damage to buildings. Wind speed
is 55-63 miles (89-102 kilometers) per hour.

whole gale

A storm causes widespread damage, but

is very rare on land. Wind speed is 64-73
miles (103-117 kilometers) per hour.

A hurricane causes violent destruction.

Wind speed is 74 miles (117 kilometers)

or more per hour.
162 |
Air, Wind, Clouds, and Weather

Measuring wind speed

Weather forecasters, aviators, sailors, and some other
people often need to know exactly how hard the wind is

To find out, they use an instrument called an

blowing.
anemometer (an uh MAHM uh tuhr). An anemometer
measures the speed of the wind.
You can make a simple anemometer for yourself.
You'll need:

four paper cups

two strips of heavy cardboard,

4x12 inches (10 x 30 centimeters)
thin cardboard or heavy paper,
4x6 inches (10 x 15 centimeters)

crayon
pencil

scissors

nail with a large head

Measure and cut the heavy

cardboard strips. Put the strips
together to make a cross, like a
plus sign. Tape the strips

together.
 163

Then make a small hole in the

middle of the cross and push the
nail through the hole.

Color stripes on one of the cups,

so that it looks very different from
the others. Then cut two four-inch
(10-centimeter) slits down the
opposite sides of each cup.
164

Slide one cup onto each arm of

the cross. Push the arms through
both slits. The ends of the arms
should stick out about 1/2 inch (12
millimeters) beyond the cups. All
of the cups should face in the same
direction.

Roll the piece of thin cardboard around a pencil to

make a six-inch (15-centimeter) tube. Tape the tube
together. Put the nail in the tube, so that the cross with
the cups rests on top. Your anemometer is ready to use.
 165

Pick up the bottom of the tube and hold your

anemometer out in the wind. The cross with the cups
will spin. Count the number of times the striped cup

moves past your arm during thirty seconds.

Divide the number you got by twenty-two. This will
give you the wind speed in miles per hour. For example,
if the striped cup went around forty-four times, divide
forty-four by twenty-two. You get two — so the wind
speed is two miles per hour.
To find the wind speed in kilometers, multiply your
answer by 1.6. Two times 1.6 is 3.2 kilometers per hour.

:
mi
 Air, Wind, Clouds, and Weather I 167

Whirlwinds!

It is late afternoon in the summer. The air is hot

and sticky. In the distance, a long line of clouds is

gathering. There is a rumble of thunder.

The line of dark clouds comes swirling over the
prairie. Small, shaggy lumps of cloud hang from the
bottoms of some of the larger clouds. A crackling rain
of hail comes pouring down, and the sky flickers with
lightning.
Suddenly, from the lumpy mass at the bottom of a
cloud, a dark cone sweeps down toward the earth. It
looks like a huge, twisting snake hanging from the
cloud. There is a terrible roaring noise!
It's a tornado!
Tornadoes are sometimes called whirlwinds or
twisters. A tornado is a spinning, whirling wind that
forms a long tube of air. Where the tube touches the
ground, terrible things happen! The whirling wind can
pick up a heavy truck and throw it through the air. It

can pull houses apart and knock big, thick trees over.

Tornadoes are caused when there is warm, moist air

beneath cold, dry air. The warm up and cools

air rises

quickly, letting go of its heat and water. This makes

hail and rain fall. Air comes rushing in from all sides
to take the place of the rising warm air. Because the
wind blows from several different directions, the air
begins to whirl.
Tornadoes can happen in many parts of the world.
But most tornadoes happen over the central part of
the United States.
168

>ft
the eye of a hurricane photographed from a space satellite
4S*
 Air, Wind. Clouds, and Weather I 169

The storm with an eye

A hurricane is a storm that's shaped like a doughnut.

It's a great, whirling circle of clouds, hundreds of miles
(kilometers) wide. In the middle is a hole where the air
is perfectly calm. This hole is called the "eye" of the
hurricane.
No one knows for sure what causes hurricanes. A
hurricane begins over the ocean, near the equator,
where the ah- is very hot, wet, and still. As great
masses of this warm, wet air rise up, towering rain
clouds form. Sometimes, something happens to start
the clouds whirling. Then, warm ah* in the center of
the clouds forms into an eye. When the wind reaches a
speed of seventy-four miles (119 kilometers) an hour,
the storm is called a hurricane.
A hurricane is a great, boiling, whirling circle of
wind and rain.The wind of a hurricane is terrible,
indeed. It may blow at two hundred miles (322
kilometers) an hour. It causes huge ocean waves that
rush ahead of the hurricane. If these waves reach land,
they can cause sudden, terrible floods. If a hurricane

blows over land, the wind can tear up big trees by the
roots and push over whole buildings.
People in the path of the eye of a hurricane know
that they will be hit by two storms. First, there is a
long line of clouds — the front of the circle. The wind
begins to blow hard. Then harder. Rain comes
 170

pouring down. The sound of the blowing wind and

rushing rain is like steady thunder.
Then, the wind dies down. The rain stops. The air

grows very hot and still. The eye of the hurricane is

passing over. It may take an hour or more to pass.

Then the back of the circle arrives. Once more the
howling wind blows and the driving rain pours down.
The wind and rain rage again, for a time. Finally, the
back of the circle moves on, carrying the wind and rain
to another place.
The United States National Weather Service uses an
alphabetical list of first names to identify hurricanes.

Each season, the first hurricane is given a name that

begins with A.

It's a Fact
.* y ' *. -<
Hurricanes have different names in

different parts of the world. They

are called cyclones when they happen
over the Indian Ocean and typhoons
in the western Pacific. In Australia,
a hurricane is called a willy-willy.
 Air, Wind, Clouds, and Weather 171

strong winds push great waves ashore during a hurricane

172 I Air, Wind, Clouds, and Weather

Dust devils and

dust storms

A tornado is a whirling wind that comes down from

the sky and touches the ground. Dust devils and
sand pillars are whirling winds that go from the ground
up into the sky.
Whenever hot air rises, it causes a wind. On a hot,

dusty prairie, or a desert, rising hot air often begins to

spin. Then, it carries up a whirling cloud of dust or

sand.
On a prairie, or on a dusty city street, these whirling
clouds are called dust devils. They never get very
high. But in a desert they sometimes go whirling up in
a thick cloud a thousand feet (304 meters) high. Then,
they are often called sand pillars.

Sometimes, when a large mass of hot desert air rises

up, the wind that rushes in to take its place causes a

sandstorm or dust storm. The wind sends the sand
rushing through the air. Great clouds of dust rise up,

turning the whole sky black. A desert storm can often

blow for hours, or even days.
 ! _ *mmt»*»***wm>*m****'*!i'

dust devil
174

Floating water in the air

Clouds. Sometimes they look like big gobs of

whipped cream in the sky, and sometimes like soft,

floating feathers. Sometimes they're white as milk, and

sometimes as dark and gloomy as an angry frown. But
what are clouds? Where do they come from?
A cloud is simply billions and billions of tiny, tiny

droplets of water or ice all clustered together. And the

water that makes clouds comes from the earth.
When you perspire on a hot, sunny day, you're
helping to make a cloud. When a mud puddle dries up
in the sunshine, it's going to become part of a cloud.
Every day, the heat of the sun dries up tons and tons
of water from everywhere on earth from lakes and —
rivers, from the ocean, and from mud puddles, plant
leaves, and perspiration. All this water is turned into
water vapor, which is water in the form of gas. This
gas goes floating up into the air.

The water vapor is warm from the sun's heat. But as

it rises higher and higher, it begins to cool. Wien it

gets cool enough, it turns back into water or ice. Then,

tiny droplets form around tiny, tiny bits of dust in the
ah*. These droplets make up the clouds.
Some clouds are all water, some are all ice, some are
a mixture. You might think the water and ice would be
so heavy it would fall to the ground, but the droplets
are so very tiny that even the slightest wind is enough
to keep them floating through the air. However,
sometimes things happen that make many droplets
collect together and become large drops. Then the
cloud falls to earth — as a shower of raindrops.
Air, Wind, Clouds, and Weather I 175
stratus clouds

Shapes in the sky

There are many different kinds of clouds, and each

kind has a name. Most clouds are named for their
shapes.
The clouds that look like great sheets pulled across
the sky are called stratus clouds. Strato means
"sheetlike." These are the kinds of clouds that are

closest to the ground.

When a stratus cloud is dark, with a steady rain

falling from it, it is a nimbostratus cloud. Nimbus
means "rain," so a nimbostratus cloud is a "rain sheet."
Cumulus clouds are the ones that look like fluffy
balls of cotton, or scoops of ice cream all piled up.

Cumulus means "pile" or "heap." When a cumulus

cloud rises high into the air and grows dark and heavy
 Air, Wind, Clouds, and Weather I 177

-*

1
cumulus cloud
178 Air, Wind, Clouds, and Weather

with rain, it is called cumulonimbus —a "pile of rain."

These are the kinds of clouds that cause thunderstorms

and tornadoes.
Stratocumulus clouds cover much of the sky, like

stratus clouds, but are piled up, like cumulus clouds.

It's easy to see how they got their name.
Alto means "high," and altocumulus clouds are
higher than stratus clouds. They may be as much as
20,000 feet (6,296 meters) above the ground. They
don't look much like piles, though. Sometimes they look
like lumpy, white ripples stretched across the sky.
Then they are called altocumulus undulatus clouds.
Undulatus means "ripple."
The highest clouds of all are cirrus clouds. They are
made of ice droplets, and look like thin, wispy streaks
or curls. And cirrus means "curl of hair." Sometimes,
cirrus clouds are piled together. Then they are called
cirrocumulus clouds. When there are lots of such
cirrocumulus clouds, people say it's a "mackerel sky,"
because the clouds look like the scales of the fish called
a mackerel.
cirrus clouds
 Squeezing water from air

Water is almost always in the air around you, even

when you can't see it or feel it. Here is an experiment
that will show you how clouds form when cold air and
warm air come together. You'll need:

a drinking glass (glass — not a spoon

paper or plastic) a pot of water
ice cubes

Do this experiment in the kitchen. To make sure the

air is damp, have a pot of water boiling on the stove.

(Ask someone for help if you need it.)

Fill the glass halfway with water. Make sure the

outside of the glass is dry. Then put some ice cubes in
the water and stir them slowly. After a few minutes, you
will see that the outside of the glass looks frosty and
feels wet. What happened?

s
 water droplets
forming on a
cold glass

The outside of the glass was dry when you began, but
the warm ah -
in the kitchen was damp. It was full of
water vapor — water in the form of a gas.
Water vapor is made up of tiny things called
molecules. These molecules of water vapor are spread
out and moving around in the air. But when some of the
molecules touch the cold glass, they condense, or come
together, to form water droplets on the glass.
Clouds form in the same way. Warm ah*, with water
vapor in it, meets cold air. Where they meet, the water
molecules get very cold. They condense and become tiny
droplets of water or bits of ice.
182

fog under the Golden Gate Bridge, California

 Air, Wind, Clouds, and Weather |
183

Clouds on the earth

Eeee-rump! Eeee-rump! The growly sound of a
foghorn echoes in the night. A thick, gray fog creeps in
from the ocean and settles over the waterfront. You
can hardly see your hand in front of your face. It's like

being in the middle of a cloud.

As a matter of fact, that's just what fog is. It's a
cloud that touches the earth, instead of floating high in
the sky.
Like every other kind of cloud, fog forms when warm,
moist air meets cool air. Fog often forms when warm,
moist air passes over the cold water of an ocean, lake,
or river. The warm air quickly cools. Then the water
vapor in it becomes millions of tiny droplets of water
— a cloud that rolls in from the water and spreads out
over the land.
Fog forms over land in much the same way. This
happens when ground that has been warm all day
begins to cool off. As the warm air above the ground
cools, the water vapor in the air turns into droplets of
water. Then there's a fog that hugs the ground.
184 I Air, Wind, Clouds, and Weather

Homemade clouds

You can make a cloud! In fact, you probably have

made clouds many, many times. All you need is a
cold day.
Just open your mouth and blow a puff of breath into

the cold air. For just a moment, you'll see a cloud.

It's only a tiny, smoky, whitish patch in the air.

But it's a real cloud.

Clouds are made when warm, moist air hits cold air.

That's what happens when you breathe on a cold

day. Your breath is warm from being inside your warm
body. And your breath is full of water vapor — water
in the form of a gas. When your breath hits the cold

air, the water vapor instantly turns into many tiny

droplets of water. The droplets form a cloud, just
like the clouds in the sky. But the cloud is so tiny
that it quickly spreads out and vanishes in the air.

'"">**** "***'"%!».
Clouds airplanes make
Have you ever looked up and seen a jet airplane high
in the sky? Sometimes you will see what looks like a
trail of whitesmoke stretched out behind the plane.
This trail is a cloud made by the jet.
The air high in the sky is cold and frosty. Hot gas,
left over from burned fuel, comes out of the jet's

engines. There is a lot of water vapor in this hot gas.

When the water vapor hits the cold air, it instantly
condenses into tiny water droplets or ice crystals. So
the jet leaves a long, white cloud behind it.

These long clouds that a jet makes are called

contrails, which is short for "condensation trail."

Contrails are also called vapor trails. Contrails
sometimes cause rainstorms or snowstorms.
 . - • • * . »
'•• • • •• • • •
f
•
.

.
•• • . • • . •

8
.•••
v-
 Air, Wind, Clouds, and Weather I 187

Sparkling spider webs

Early in the morning, when the sun chases the
night's shadows from lawns, gardens, and meadows, the
ground is full of sparkles. Dewdrops, like tiny jewels,

are everywhere. They glitter on spider webs, glisten on

leaves, and gleam on blades of grass.

But if the ground was dry the day before, and there
was no rain during the night, where did all the
sparkling dewdrops come from?
Dew forms on still, clear nights when the air is warm
and moist and the ground is cool. When the sun goes
down, leaves and grass and spider webs and other
things out in the open grow cool. As the moist air

touches them, it grows cool, too. Then, the molecules

of water vapor in the air rush together. They form
tiny drops of water that coat the leaves, grass, spider
webs, and other things. These tiny drops slowly run
together and form the bigger drops of dew that greet
the morning sunshine.
You can make dew with your breath. When you are
inside on a cold winter day, blow your breath gently
against a windowpane. A small, grayish patch will form
on the Blow some more and tiny drops of water
glass.

will form. Blow again and the drops will begin to run

together and make bigger drops. This is how dew

forms.
188 Air, Wind, Clouds, and Weather

How much did it rain?

You've probably heard weather forecasters on radio

or television tell how many inches or centimeters of
rain fell during a storm. But how do they know how
much rain fell?
Scientists measure rainfall with an instrument called
a rain gauge. Rain falls into the gauge during a storm.
Afterwards, scientists measure the amount of water in
the gauge.
You can make a simple rain gauge out of a clean
coffee can and a ruler. Place the can in the open, away
from trees, so that rain can fall directly into it. Bury
it partly, or wedge it with heavy stones so it can't
move.
As soon as the rain has stopped, measure the amount
of water in the can. Make sure the end of your ruler
touches the bottom of the can. Lift the ruler straight
up and see how much of it is wet. Then you will know
how many inches or centimeters of rain fell.
 ''
.'.
( t«.
190

Flash and bang

Oh, oh — you're caught in a rainstorm! The sky is

dark and angry and rain is spattering down all around
you. Suddenly, a zigzag flash of lightning brightens the
sky for just an instant. Almost at once, there's a
tremendous ripping sound and then a crash of thunder!
What causes these bright flashes and loud crashes
that make a rainstorm so scary and exciting?
Lightning is caused by electricity. Each tiny drop of
water in a rain cloud has a tiny charge of electricity.
There are billions of water drops in a cloud, so the

whole cloud has a powerful charge of electricity.

Sometimes the charge inside the cloud is so powerful

that electricity flashes from one part of the cloud to
another. And sometimes, when the cloud comes near
another cloud with an electric charge, or near the
ground, electricity rushes between them. So, the flash
we see when lightning snakes through the sky is really

a huge electric spark.

A flash of lightning heats up the ah* around it. The
heated air goes rushing out in all directions. It slams
into the cold air, making it shake. This is what causes
the crash of thunder.

It's a Fact

You can tell how far away

lightning is. Count the
seconds between the flash

and the thunder. Every five

seconds equals one mile
(1.6 kilometers).
&$k*fajji
The bridge in the sky

Long ago, people thought that rainbows were magic.

Some people believed that a rainbow was a bridge that
appeared in the sky when the gods wanted to leave
heaven and come down to earth. People also believed
that if you could find the end of a rainbow — where it

touched the earth — you would find a pot of gold.

Today, we know that a rainbow is simply caused by

sunlight shining through raindrops. To see a rainbow,
 Air, Wind, Clouds, and Weather j
193

you must have the sun behind you and the rain falling
in front of you. Sunlight looks white, but it is really

made up of many colors. When sunlight enters a

raindrop, it breaks up into violet, blue, green, yellow,
orange, and red. We see these colors in the rainbow.
But because the colors blend, we usually see only four
or five of them.
Many rays of sunlight, breaking up into their colors
and reflecting off many drops of falling rain, make a
shimmering, curved, colorful rainbow. If the rain is

heavy, both ends of the rainbow may appear to touch

the earth, many miles (kilometers) apart.

Turn on a hose. Adjust the nozzle

to a fine spray. Stand with your
back to the sun. You'll see a
rainbow shining in the spray.
194 Air, Wind, Clouds, and Weather

Beads and balls of ice

Hail and sleet are frozen rain. But they are very
different. Sleet is tiny beads of ice. Hail is lumps of ice

and snow that may be as big as baseballs!

Hailstones begin as ordinary raindrops in a rain
cloud. Gusts of wind carry them up to the highest part
of the cloud. Here, where the air is freezing cold, the

raindrops turn to ice. Snow forms in this part of the

cloud, so the drops of ice get a coating of snow. Then

they are so heavy, they fall.

As they fall back into the part of the cloud where

other raindrops are forming, they are covered with
water. Again, a gust of rising wind catches some of
them and lifts them up. The coat of water freezes, and
they get another coat of snow. Again, they fall.

Hailstones may rise and fall this way many times.

Each time, they grow a little bigger and heavier.
Finally, they become so heavy the wind can't lift them
any more. They keep falling until they come to earth
where they rattle on roofs, smack against leaves, and
bounce on the grass.

Sleet is made when tiny drops of very cold water in a

cloud get mixed with falling snowflakes. The snow and
water freeze together into little beads of ice that sting

your face and pop against windowpanes.

hailstones in a cornfield

Hailstones begin as raindrops.

They are carried up into cold
air, where they freeze. As

they fall, they are covered

with layers of snow and ice.
This often makes them grow as
big as golf balls —or bigger!

the inside of a hailstone

This large hailstone has

been sawed in half to show
the many layers of snow
and ice inside it.
 Lacy crystals
Look up during a snowstorm. Watch
the snowflakes come spinning down out of
the sky. You can see that snowflakes
aren't drops, like rain; or lumps, like hail;
or tiny beads, like sleet. They look more
like little ragged feathers.
When you look at a snowflake through
a magnifying glass, you see a beautiful,
six-sided, lacy shape. Even though most
snowflakes are different from each other,
they all have this kind of shape. A small .tj.^-.

snowflake is made of just one of these 1

shapes, or crystals, but large snowflakes
are made of several crystals stuck
together. Sometimes snowflakes are as
big as large coins.
*@
Snowflakes are formed high at the top
of storm clouds, where the ah" is freezing
cold. Each snowflake is a tiny bit of

* ¥
water vapor — gas — that freezes suddenly,
without first changing into water. Because
* 1
of this, instead of becoming a bead or
ball of ice, it becomes a lacy crystal that
forms around a tiny bit of dust.

Snow can form high in the sky, even in

summertime. But when snow falls in

summertime, it melts and becomes rain

as soon as it reaches warm ah*.

vr HtfM
198 Air, Wind, Clouds, and Weather

Sparkly pictures
on your window
The door was shut, as doors should be

Before you went to bed last night;

Yet Jack Frost has got in, you see,

And left your window silver white.

He must have waited till you slept;

And not a single word he spoke,
But -pencilled o'er the panes and crept
Away again before you woke.

From Jack Frost

Gabriel Setoun

On a cold, crisp day in late autumn or winter, you

may wake up to find your windows covered with icy,
lacy swirls. They weren't painted by Jack Frost, of
course. They were made when tiny droplets of water
in the air got so cold they froze on the windowpane.
During the day, the outsides of your windows are
warm, both from the heat inside your house and from
the sunshine. But when the sun sets, the windowpanes
grow cool, then cold. The air touching the window
grows cold, too, and all the tiny droplets of water in
the air freeze. They suddenly become crystals of ice,
stuck to your windowpane. Then you see designs like
lacy coils, sparkly feathers, and shiny, silvery leaves.
>'g
200 I Air, Wind, Clouds, and Weather

Icy daggers
It's a bitterly cold winter day. Snow lies in a great
white sheet on the ground and on the roof of your
house. The roof is warm from the heat inside the house,
so the snow on the roof is slowly melting. Tiny trickles
of water run to the edge of the roof. Drops of water
begin to form.
Some of the drops grow bigger and fall to the ground.
But many of the drops freeze in the cold air. They
become bits of ice hanging along the edge of the roof.

The water trickling off the roof runs onto the ice. The
bits of ice get thicker and longer as more and more
water freezes on them.
All day long, water trickles down the pieces of ice.

Water drops form at the end of each piece of ice. The

drops hang there for a moment. Before they can fall

off, they freeze. Slowly, the pieces of ice become the

long daggers we call icicles.

Icicles can be short or long, thin or fat. It depends

on how much snow melts and how fast the water drips
from a roof or tree branch. An icicle can be shorter than
your little finger or as long as your whole body.
 lii i:j

Planets,
Stars, and
Galaxies
204 Planets, Stars, and Galaxies

The black emptiness

Space is — emptiness.
It is black because emptiness has no light of its

own. It is neither cold nor hot because emptiness has

no temperature. And, of course, there is no air or

water in space.
But although space itself is emptiness, there are
things in it. There are billions and billions of stars.

There are huge clouds of gas and dust. Comets and

chunks of rock called meteoroids rush through parts of
space. Waves of light from stars travel through it.

Tiny, invisible particles move about. Space is the

emptiness that surrounds all these things.
Space and all make up what we call
the things in it

the universe. We do not know how big the universe

is, but the things farthest away that we know about

are very far away. The light they give off takes
thousands of millions of years to reach us! Perhaps
the universe stretches away in all directions,

forever —and never ends!

It's a Fact

About 1,300,000 planets the size of

earth could be packed into the sun.

The bright giant

Millions of miles (kilometers) out in space there is a

gigantic ball of hot, glowing gas we call the sun.
The sun is actually a star. It is the closest star to
us. Its official name is Sol, which was the name of the

ancient Roman sun god. From the name Sol comes

our word solar, which means "of the sun."
The sun is enormous! At least 1,300,000 planets the
size of earth could be packed into it. And there
would be room left over. And yet, big as the sun is,

many other stars are much, much bigger.

Although it is big, the sun looks small. That's
because it is so far away. It is about 93 million miles
(150 million kilometers) from the earth. It takes light
208 Planets, Stars, and Galaxies

from the sun about 8 minutes and 20 seconds to

cross that enormous distance and reach our world. And
light is the fastest moving of all things.

The sun is tremendously hot. The hotter a thing is,

the more brightly it glows. The sun glows so fiercely
that we can't look straight at it, even though it is
so far away. But the sun is not actually burning.
It isn't a ball of fire. It's a ball of gas, squeezed together
so tightly that its center is actually solid. This makes
the center tremendously hot. It is really a kind of giant

atomic furnace in which the temperature is about 27

million degrees Fahrenheit (15,000,000° Celsius)
Energy pours up from inside the sun to the surface.

The surface is a boiling, bubbling mass from which

great spouts of glowing gas leap up — sometimes as much
as a million miles (1,609,000 kilometers) into space!

the sun

The sun is a star. It is a giant ball

of gas squeezed together so tightly

that it is tremendously hot.

V
m
1
wtmtmmmm
 Planets, Stars, and Galaxies |
211

How the sun was born

Most scientists think our sun began as an immense
cloud of gas and dust.
Stars that are growing old often shoot out enormous
clouds of gas and dust. The gas and dust are made
up of all kinds of chemicals. There are many such
clouds in space. As these clouds move through space,

they pull more and more gas and dust into themselves.
Gravity pulls all the gas and dust together, tighter
and tighter. Over many millions of years, the center

of the cloud of gas is pulled into the shape of a gigantic

ball.

Gravity squeezes this gas ball together so tightly

its center is more dense than steel ! When gas is

squeezed together that tightly, it becomes tremendously

hot. The center of the gas ball grows so hot that
itbecomes an atomic furnace. The ball begins to glow
with this fierce heat. It has become a star!
This how all stars seem to form. Right now, out
is

in space, new stars seem to be forming out of clouds

of gas. And scientists think this is how our own

sun began, about five billion years ago.

212

Mm
The source of life

Without the sun, there could be no life on earth.

Energy pours up out of the raging hot atomic
furnace that is the center of the sun. It moves up to
the sun's seething, boiling surface and rushes out
into space as waves of light.

The waves of sunlight spread out in all directions.

They travel at the tremendous speed of 186,282 miles
(299,792 kilometers) per second. Most of them speed
on into the endless darkness of space. But some
head straight toward a small, bluish planet that lies

in their path. It is earth.

The waves of sunlight pass through earth's

atmosphere and travel down to the planet's surface.
 Planets, Stars, and Galaxies 213

There, the light waves strike the leaves of green

plants — trees, bushes, and blades of grass.
Green leaves are made of millions of tiny cells, like

little bags. In each cell there are little blobs of green

stuff called chlorophyll. When sunlight passes into a
leaf, the little blobs of chlorophyll catch and hold tiny
bits of the light — sparks of the sun's energy.
Plant cells are like factories, where the plant's food is

made. Using the captured sunlight for power, the

green blobs of chlorophyll turn water and carbon

dioxide gas into a kind of sugar. This sugar is stored-

up energy. The plant uses the stored-up energy for the

fa&

A
214

power to grow. Without energy from the sun, the plant

couldn't grow or live.
A steer moves slowly through a field of grass. Each
plant it eats has some of the stored-up energy. The
energy is taken in by the steer's body and used for the
power to make the steer live and move. Without the
stored-up energy it gets from the plants it eats, the

steer could not stay alive.

The steer is part of a herd being fattened for market.
In time, the steers' bodies will be turned into steaks,
 Planets, Stars, and Galaxies 215

roasts, and hamburgers for people to eat. The energy

in the steers' bodies will go into peoples' bodies,
where it will be used to keep them alive. And, of course,

people also eat many kinds of plants for the energy

that's in them.
All living things must take in energy in order to
stay alive. And nearly all energy comes from the sun.
So the sun gives us much more than just light and
heat. It truly gives us life.
216
 Planets, Stars, and Galaxies I 217

Moving into daytime

Imagine that you have awakened very,
very early. You look out of a window.
The sky is still black, and the whole
world seems dark and silent.

But as you watch for a long time, the

sky slowly turns from black to gray.
You can begin to see things. The sky
grows lighter. A pink glow spreads across
the eastern horizon. Suddenly, you can
see the tiniest tip of fiery red peeping over
the edge of the land. The sun. Slowly,
more and more of it becomes visible as it
rises up into the sky.

This is the time of day that is called

sunrise. But the sun doesn't really rise. It
just looks as if it is moving up into the
sky. What is really happening is that the
part of the world you live on is turning
toward the sun.
Half of the earth is always covered
with light from the sun. The other half
is always in darkness, for no sunlight
can fall upon it. But the earth is always
turning. As it turns, everything on it

moves from darkness into sunlight, again

and again. This is our night and day.
218

evening

morning

When it is morning for you, your part of the world

is turning out of the darkness into the light. At
sunrise, you are just on the edge of that half of the

world that is in sunlight.

As the earth continues to turn, more and more

sunlight falls upon the part of the world where
you live. The sky grows brighter, and the sun seems to
rise higher. But the sun isn't really moving. You are

moving beneath it. When your part of the world

has moved directly into line with the sun, the sun
seems to be at its highest place in the sky. This is the
time of day we call noon. The light is strongest then.
Shadows are shortest.
As the earth keeps turning, your part of the world
moves away from the sun. This makes it seem as
 Planets. Stars, and Galaxies 219

if the sun is moving down in the sky. Shadows grow

longer.
The earth turns until your part of it is once again
on the very edge of the half that is in the sunlight.
Xow it is evening. The sky is darkening as you leave
the light behind. This is the time we call sunset,

because the sun looks as if it is dropping down behind

the curve of the earth. Slowly, the part of the world
where you live slips completely out of the sunlight.
Xow, you are turning toward the darkness of space.
It is night in your part of the world. You're getting
ready for bed. But, halfway around the world from
you, other children are waking up. Their part of
the world has turned to where your part was this
morning. For them, the day has begun.
220

spring

summer
 Planets, Stars, and Galaxies 221

The four seasons

Summer. Trees burst with thick loads of leaves.

Flowers nod in soft, warm breezes. Insects buzz. A blue

sky holds a bright, hot sun.
Winter. Bare trees stand like bony skeletons against
a cold, gray sky. Snow blankets the ground. The sun
seems pale and far away.
What causes this difference? Why is the earth warm
in spring and summer and cold in winter and fall?

Summer comes to your part of the world when a lot

of the sun's hot light falls steadily upon it. Winter

comes when not as much of the sun's light reaches your
part of the world. Then, the ground and air cool off.

winter
222

The difference in the amount of sunlight is caused

by the tilt of the earth. Earth's North and South poles
don't point straight up and down, they are tilted.
Thus, when the earth is at one end of its path around
the sun, the North Pole is tilted toward the sun and
the South Pole is tilted away from the sun. Then,
most of the sun's light falls upon the northern half of

the world, keeping it warm. This causes summer.

Because the southern half of the earth isn't getting as

much light, it is cool. This causes winter.

The earth moves on around the sun. When it has
moved about one-fourth of the way around, the
northern part gets less light than it did, so it grows
cooler. This brings autumn to the north. The southern
part gets more light than it did, so it starts to warm
up. This causes spring in the south.
When moved halfway around the sun,
the earth has
the North Pole is tilted away from the sun, and the
South Pole is tilted toward the sun. Now, the southern
part of the world gets the most light and the northern
part gets the least. So, people in the northern part
shiver in winter's cold, while those in the southern part
enjoy summer.
One part of the earth always has summer. A band
around the middle of the earth, where the equator
is, always gets about the same amount of sunlight. So,
it always stays hot.
 Planets, Stars, and Galaxies |
223

spring in the
Northern Hemisphere

autumn in the
Southern Hemisphere

autumn in the
Northern Hemisphere

spring in the
Southern Hemisphere
224

Who stole the sun?

It's the middle of the day. The sun hangs big and
bright in the sky. But, what's this? The sky seems to be
growing dark. Is there going to be a storm? No, there
are no clouds. Why is the sky getting dark?
One edge of the sun The sun
seems to disappear!
grows dim! Slowly, more and more and more of it
vanishes, as if big bites are being taken out of it.

Finally, the sky is nearly as dark as night. Where the

sun was, there is only a dark spot, with a pale, fuzzy
ring around it! What has happened?
What has happened is simply that the moon, which
moves around the earth, has passed between the earth
and the sun. The sun is much bigger than the moon, but
it is so far away that the moon can cover it up, just as

you can cover up a distant house when you hold your

hand before your face. When the moon is between the
sun and the earth, the moon throws a shadow on the
earth. The part of earth covered by the shadow is in

darkness. When the moon gets between the earth and

the sun this way, it is called a solar eclipse.

A solar eclipse can't be seen over the whole world. It

is only seen from the part of earth that is directly in line
with both the sun and moon. The moon's shadow is

never wider than about 170 miles (274 kilometers).

When the whole sun is covered up, it is called a total

eclipse. Sometimes, only part of the sun is covered. That

is called a partial eclipse. An eclipse never lasts more
than about seven and a half minutes. Never look directly
at an eclipse, not even with sunglasses or through film.

Your eyes could be badly injured!

 Planets, Stars, and Galaxies I 225

partial eclipse

total eclipse

moon

total eclipse
 Planets, Stars, and Galaxies |
227

Our next-door neighbor

As earth whirls along on its endless journey through
space, it has a companion that is always beside it

the moon. The moon is a small planet. It is only about

one-fourth as big as earth.
The moon is our nearest neighbor in space. The stars
are billions of miles (kilometers) away. The sun is
millions of miles ( kilometers) away. But the moon is

only about 239,000 miles (384,000 kilometers) away.

That makes the moon truly a next-door neighbor.
In a way, the moon "belongs" to earth. Just as
earth moves around and around the sun, the moon
moves around and around earth. It is held in place by
the tug of earth's stronger gravity. A planet that
is held by another planet this way is called a satellite.
The moon is earth's satellite.
The moon is a ball of gray rock, some of which is

covered with dust. It has no air or water — and, of

course, no plants or animals. Its whole surface is nothing
but mountains and plains of rock. When we look
up at a full moon, we can often see dark patches. These
dark places are the lowlands. They seem to form
a shadowy face that people have named "the man in
the moon." The brighter parts of the moon are the
highlands.
In ancient times, many people worshiped the moon.
The Romans, who thought the moon was a goddess,
named it Luna. Our word lunar means "of the moon."
228

Why the moon shines

Why does the moon shine? It isn't a ball of hot, glowing

gas, like the sun. It's a ball of cold, hard rock. How

can rock give off light?

The answer to that may surprise you. The moon is

like a giant mirror. The light it sends to earth is

light that is reflected from the sun.

The moon isn't really a very good mirror. It isn't
a bit smooth and shiny. In fact, most of the rock
on the moon is rough and dark gray. It doesn't really

reflect much sunlight. But sunlight is so bright that

even the tiny bit that is reflected from the moon
makes the moon look like a glowing ball in our sky.
Actually, earth is a mirror, too! It reflects some of

the sunlight that falls on it. And it's a better mirror

than the moon!
Planets, Stars, and Galaxies 229
230 I Planets, Stars, and Galaxies

Why the moon

"changes" shape
Oh! look at the moon,
She is shining up there;

Oh! mother, she looks

Like a lamp in the air.

Last week she was smaller

And shaped like a bow;
But now she's grown bigger,

And round as an 0.

from, Oh! Look at the Moon

Eliza Lee Follen
 231

#'%
half moon

full moon

The moon does, indeed, seem to change

from a slim bow into a fat, round
crescent moon
and back to a bow again. These changes
take place as the moon goes around the
earth. We call these changes phases.
In its first phase, the moon can't be
seen at all. It is between the earth and the
sun.The sun shines on the side of the
moon that is turned away from us.
Because of this, we can't see the dark
side that faces us.
After a day or two, the moon moves
You can see for yourself why
the moon has phases. You'll
need a bright flashlight, a large

ball, and a dark room. The

flashlight acts as the sun,

the ball is the moon, and you far enough to one side of us so that we
will be the earth. can see a tiny bit of the side that is

lit by the sun. From earth, this tiny bit

looks like a silvery bow. We call this

phase a crescent moon.

After seven days, the moon has moved
enough so that we can see half of its
sunlit side. This is a half moon.
After about two weeks, the moon is

halfway around the earth from where it

started. Now we can see the whole side of

the moon the sun shines on. It is now a
bright, round, full moon. As it moves on
around the earth it becomes a half moon,
then a bow again. Finally, its dark side
is again turned to us.
 Planets, Stars, and Galaxies 233

full moon

Sit directly between the light

and the ball. The whole side of

the ball facing you will be in

light, just as a full moon is.

j
r

half moon

Move the ball to your left. Go

back to where you were and face
the ball. Only half the ball will

be in the light, like a half moon.

crescent moon

Move the ball nearly between you

and the light. Most of the ball will

be in shadow. Only a small part

will be lit, like a crescent moon.
234

Shadow on the moon

The night is clear and starry. There's a bright, full
moon in the sky. But, then, a tiny, curved shadow
appears on the edge of the moon. Slowly, the shadow
creeps over the moon. More and more moon
of the

is covered by it! And, finally, the whole moon is in

shadow.
That's what happens during an eclipse of the moon.
An eclipse of the moon is called a lunar eclipse. It
takes placewhen the earth comes between the sun and
the moon. When that happens, the earth casts a shadow
on the face of the moon, darkening it.

The moon is seldom completely darkened by the

earth's shadow, however. Some of the sunlight passing

the earth gets "bent" by the earth's atmosphere.

This light is reflected onto the moon. So the moon is

still faintly visible. Thus, an eclipse of the moon isn't as

exciting as a solar eclipse.

 Planets, Stars, and Galaxies 235

an eclipse of the moon

An eclipse of the moon takes place

when the earth comes between the
sun and the moon. Then the earth's
shadow covers up the moon.
236 Planets, Stars, and Galaxies

The far side of the moon

For hundreds of years, ever since people have
known that the moon was like a planet, they have
wondered about something. They have wondered what
the far side of the moon was like.

You see, even though the moon spins around, we

never get to see all of it. The tug of earth's gravity
causes the moon to spin very slowly. In fact, the moon
only spins around once in the time it takes to go all the
way around the earth. As a result, the same side of the
moon always faces the earth. The diagram on the
opposite page shows how this happens.
People wondered what the moon's far side was like.

Was it bare and rocky, like the side we can see? Or was
it different? Was it possible that there might be water,
plants, and animals living on the side we cannot see?
We don't have to wonder anymore. In 1959, a Soviet
spaceship went around the moon. There was no one on
this ship, but there were cameras that took pictures of
the moon's far side. Later, other Soviet and American
spaceships, some with people in them, took more
pictures. The pictures showed that the far side of the
moon is just as bare and rocky as the side we see.

we now know something that all the billions of

So,
people who lived before us didn't know. We know what
the far side of the moon looks like.
 mtm

the far side of the moon

This diagram shows why we can

never see the moon's far side.
Even though the moon makes one
full turn as it goes around
the earth, its far side (shown
by the flag) is never turned
toward us.
238

On the moon
People have visited the moon and walked on it, so
we know what the surface of the moon is like. This
big ball of gray rock has broad, flat plains covered with
powdery rock dust. There are rugged mountains. And
there are thousands of billions of round pits called
craters.

The craters were made by chunks of rock that

smashed into the moon like bullets. Such chunks of
rock, called meteoroids, move around the sun, just
as the earth and moon do. During the billions of years
since the moon was formed, billions of meteoroids
have bumped into it. The moon and the meteoroids
were moving so fast when they crashed together, that
the meteoroids dug craters in the moon's surface.
Now, the moon is pitted and pocked with these craters.
Some of the craters are no bigger than pinheads,
some are the size of a car tire, some are hundreds of
feet (meters) wide. But most are about five to ten

miles (8 to 16 kilometers) wide. The biggest is about

seven hundred miles (1,100 kilometers) wide. When
the meteoroids struck, they usually threw up walls of
rock around the craters they made. The moon's
mountains are really the walls of huge craters.

There is no air on the moon to scatter the sunlight,

so even in daytime the sky is pitch black and filled

with stars. Because the moon turns so slowly, one day

on the moon is as long as fourteen days and nights
on earth. During the moon's daylight hours, the rocky
surface grows so hot it would burn you if you touched
 Planets, Stars, and Galaxies 239

the surface of the moon

This is the part of the moon where American astronauts landed

in 1972. In the background are part of the Taurus Mountains.
240 Planets, Stars, and Galaxies

it. But during the long night, the moon grows colder
than the coldest place on earth.
The moon's gravity isn't as strong as earth's gravity.
On the moon, you could jump six times higher than
you could on earth, and lift things that would be
too heavy for you to lift on earth.
With no air, there is no sound on the moon. And
there is no wind to stir the rock dust that lies thickly
on the plains. The moon is a still, silent, barren,
lifeless place, unlike any part of earth.

a moon crater
 | i ^ B

,-
»-&«?

-» <#*;

:'..
-

an astronaut walks upon one of

the moon's barren plains

an astronaut's footprint
in the powdery moon soil
^^
r-.." j 1
'-r «**
242 I Planets, Stars, and Galaxies

The sun's family

The planet earth is part of a family. It is one of nine

planets that belong to the sun. We can see some of
these planets at night, shining like bright stars. Like
the earth and the moon, the other planets all shine
with reflected sunlight.
Each planet moves around the sun in a path called
an orbit. There are many millions of miles (kilometers)
between the planets. Two planets are closer to the sun
than the earth; the others are all farther away. Four
planets are smaller than the earth; four are much
bigger. Seven of the planets have moons, or satellites.

Saturn
 Mercury W

Venus «e
Earth
fc k
V
Mar's V.
v >

asteroid bell k
r.

• • • '

7 •
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-. & -

Jupiter "
#
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% *
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-"V V.N

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•: . .

Planets and moons aren't the only things whirling

around the sun. There are also billions of chunks of

rock and metal called meteoroids. There is a ring

of much larger chunks of rock and metal, like small
planets, called asteroids. There are comets, clouds
of drifting gas, and bits of dust.

All these things are tied to the sun by its gravity.

They are the sun's "family," called the solar system.

244

3
5-X v»

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^ &
A

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5>* , iT<

Closest to the sun

The planet closest to the sun is Mercury. It is one

of the smallest of the nine planets —only a little more
than one-third the size of the earth. Seen from the
earth, Mercury appears, disappears, and appears again.
This is why it was named after the Roman god
Mercury. As the messenger of the gods, Mercury was
thought to move swiftly back and forth between
heaven and earth.
Mercury, much like our moon, is a bare, rocky ball
covered with billions of craters. In Mercury's sky,
the sun appears many times bigger and brighter than
it looks from earth. This is because Mercury is only
about 36 million miles (57.9 million kilometers) away
from the sun. The side of Mercury facing the sun is

tremendously hot. The other side is fiercely cold.

A year on Mercury is only as long as 88 of our days.

That's how long it takes Mercury to move all the
way around the sun. But a day on Mercury is equal
to 59 of our days! Mercury spins around so slowly that
its day is nearly as long as its year.
 Planets, Stars, and Galaxies |
245
'*.**'

the surface of Mercury

Mercury is very much like our

moon. It is a bare ball of

rock, covered with craters.

Mercury

ay.
246

Venus
 Planets, Stars, and Galaxies 24"!

j j

Earth's "twin

The second closest planet to the sun is Venus. Seen

from the earth, it is the brightest of all the stars and
planets in our sky. Sometimes it can even be seen in

daylight. Because of its beauty, it was named after the

Roman goddess of love and beauty.

Venus is nearly the same size as the earth and is

often called the earth's "twin." But Venus is really

nothing at all like our world.

Like the earth, Venus has an atmosphere — but the
"air" of Venus is full of poisonous gases. It is filled with
such thick clouds that we can't see the surface of the

planet. These clouds contain droplets of sulfuric

acid — a chemical so strong it can dissolve metal!

High in Venus' atmosphere, there are terrible
windstorms, with winds that blow harder than the
strongest hurricanes on earth. The sky is lit by
constant flickers of lightning that flash as often as
twenty times a minute.
Because Venus is always hidden by clouds, scientists
have used spacecraft to photograph its surface and test
its soil. We now know that the surface of Venus is so
hot it would melt lead. There is no water, nor any
other liquid, anywhere. Much of the surface is a huge,
rolling plain, but there are also great mountains, long
and deep canyons, and big and small volcanoes, some
of which may be active.
Venus is about 67 million miles (108 million
kilometers) from the sun. Its year is as long as 225 of
our days. But its day is as long as 243 of our clays. On
Venus, a day is longer than a year!
The red planet

At night, you can sometimes see a

* *"
bright "star" that shines with a reddish
gleam. It is Mars, the "red planet,"
named after the Roman god of war. Mars
is the fourth planet from the sun
—about 142 million miles (228 million
kilometers) away.
Some parts of Mars look like the moon.
But Mars isn't a dead world like the
moon. It has a thin atmosphere made up
of several gases, and thin blue and thick
'J&
white clouds move across its sky. Fierce
windstorms whirl sand up from the plains *-#

%jS
 Planets, Stars, and Galaxies 249

the surface of Mars

This picture was taken by a

space vehicle that landed on
Mars. The orange sky is caused
by red dust in the atmosphere.

t* XKL.

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250 Planets, Stars, and Galaxies

The north and south

poles of Mars are
covered with snow,
just like the poles

on Earth.

Volcano on Mars

A giant volcano on Mars

can be seen near the top of
this photograph.
 251

a Martian moon

Phobos, Mars's largest moon, is a

lumpy rock about fourteen miles
(23 kilometers) wide.

and fill the air with dust. This dust gives

the Martian sky its strange orange color.
There are volcanoes on Mars. One of
them is two times higher and many times
wider than Mount Everest, the highest
mountain on Earth. There are also
canyons on Mars. One of these canyons is

as wide as the whole continent of North

America. And it is many times deeper
than the earth's deepest canyon, the
Grand Canyon of the Colorado River in

Arizona.
Mars has two little moons that are just
lumpy chunks of rock. The largest, called
Phobos, is about fourteen miles (23
kilometers) wide. The other, Deimos, is

about six miles (10 kilometers) wide.

Mars is only about half as big as the
earth. Its year is nearly twice as long as
ours, but its day is about the same.
 9Ki
HI

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The Great Red Spot seems

to be a giant hurricane.

Jupiter Earth

'llSfliBmll
 Planets, Stars, and Galaxies I 253

The giant planet

The giant of the sun's family is the planet Jupiter.

It's the biggest planet of the solar system — more than
eleven times bigger than the earth. Jupiter is named
after the king of the Roman gods.
The earth, the moon, and Mars are solid rock, but
Jupiter is very different. Although it may have a small
rocky core, most of this huge planet is a ball of hot
liquid surrounded by thick clouds of gas. The clouds
form colored bands around the planet. There is also a

strange spot called the Great Red Spot. It seems to be

an enormous hurricane, more than three times as wide

as the earth is thick. It has been whirling in Jupiter's
atmosphere for hundreds of years. And other wild
windstorms are always raging in Jupiter's thick clouds.

Jupiter has sixteen moons. The smallest moon isn't

as big as most of the earth's mountains. The biggest,

called Ganymede, is bigger than the planet Mercury.
One moon, called Io, has erupting volcanoes.

Jupiter is surrounded by a very thin ring of dust.

This ring may be what is left of a moon that came too
close to Jupiter. The tremendous pull of Jupiter's

gravity would have torn it apart.

Jupiter is about 484 million miles (778 million
kilometers) from the sun. A year on Jupiter is about 12
earth-years long, but a day is only about 10 hours.
Scientists have used space probes to study Jupiter.
In 1977, Voyager 1 and Voyager 2 were launched in

the United States. Both probes flew past Jupiter and

Saturn. Voyager 1 found Jupiter's ring, and Voyager 2
photographed the four largest moons.
254

A many-ringed planet

The sixth planet from the sun is Saturn. It is the

second largest planet — nearly ten times bigger than
the earth. Saturn is named after the Roman god of
farming. It has a rocky center, probably covered by a
thin layer of liquid, and is surrounded by thick clouds
of gas. Big as it is, Saturn isn't even as thick or heavy
as a ball of water the same size. In fact, if there were
an ocean big enough to hold it, Saturn would float!

Saturn is surrounded by seven flat rings, one inside

the other. These rings are made up of thousands of
narrow ringlets. The rings are formed of billions of
pieces of ice, from tiny specks to very large
"snowballs." The bits of ice circle around Saturn just as
the moon circles the earth. Scientists think these bits

are either material left over when Saturn was formed,

or the remains of an icy moon that broke up.
Beyond its rings, Saturn has twenty-three moons.
Most of them are chunks of ice mixed with rock. They
range in size from less than 25 miles (40 kilometers)
wide to more than 3,000 miles (4,800 kilometers) wide.
The largest moon, Titan, is bigger than the earth's
moon and has a thick, cloudy atmosphere.
Saturn is about 885 million miles (1.4 billion

kilometers) from the sun. Its year is almost 30 earth-

years long, and its day is about IOV2 hours.
Scientists used the space probes Voyager 1 and
Voyager 2 The information from the
to study Saturn.
two probes helped them find nine of Saturn's moons
and prove that Saturn had a seventh ring.
Planets, Stars, and Galaxies I 255
256

SJHKP

Neptune Earth

visiting the farthest planets

Space probes have visited

Uranus and Neptune. Someday,
we may send a space vehicle to
Pluto, the farthest planet.
 Planets, Stars, and Galaxies 257

Neptune, the eighth planet, was named after the

Roman god of the sea. It is about 2.8 billion miles (4.5
billion kilometers) from the sun. Neptune is also mostly
made up of gases, but its center may be a mixture of
slush and rocks. Its year is about 165 earth-years long,
and its clay is about 17 hours. Like Jupiter, it has
strong winds and a large spot, the Great Dark Spot.
Neptune has four rings and eight moons. The largest
moon, Triton, has "volcanoes" that give off gases and
slushy ice.

Pluto, the ninth planet, was named after the Roman

god of the dead. It is about 3.7 billion miles (5.9 billion
kilometers) from the sun. At that distance, the sun
probably looks like only a very bright star. Pluto is

made up of frozen gases, and it is mostly ice. Its year

is about 248 earth-years long, and its day is about 6
earth-days. It has one tiny moon.

Neptune
 Planets, Stars, and Galaxies 259

The tiny planets

Just as there are giant planets in the sun's

family — Jupiter and Saturn — there are also "dwarf"
planets. These small planets are called asteroids.

Asteroids circle the sun in a ring between Mars and

Jupiter. There are thousands of them. Most are less

than a mile (1.6 kilometers) across. Some are several

hundred miles (kilometers) across. The largest asteroid,

named Ceres, is about 600 miles (1,000 kilometers) wide.

The larger asteroids are nearly ball-shaped, like the
bigger planets. But the smaller asteroids are bumpy
and jagged. They may be pieces of larger asteroids, for
asteroids often bump into each other and break into

smaller bits. When this happens, they are knocked out

of their paths and into new ones. They become
meteoroids that sometimes collide with other planets.
Such collisions made the craters on the moon, Mars,
and Mercury. Bits of asteroids also become the
"shooting stars" that we see from earth.
260 Planets, Stars, and Galaxies

"Shooting stars"

A big lump of rock and metal — a meteoroid — rushes

through the blackness of space. For billions of years,

ever since the planets were formed, it has been zipping

around and around the sun. But now it is about to
meet its end. The lump of rock is heading straight
toward a huge, blue ball — the earth.

The rocky lump hurtles through space and into the

earth's atmosphere. Almost at once it begins to glow
red-hot. It is traveling at such tremendous speed that
earth's air is rubbing hard against it. This friction
makes the lump of rock grow hot, just as your hands
get warm when you rub them together.
The rock turns from red-hot to white-hot. Bits of it

burn up, leaving a trail of glowing gas. Seen from the

surface of the earth, the burning rock looks like a
bright streak, flashing across the sky. A child looks up
and sees it. "Look, Mother!" the child says. "A
shooting star!"
That's what a "shooting star" or a "falling star"
is — a meteoroid from outer space that comes into

earth's atmosphere and burns up. But when a

meteoroid comes into our atmosphere and burns, we
call it a meteor.
As many as 200 million meteors come into earth's

atmosphere every day. Most of them are quite small,

and burn up completely. But if a meteor is big enough,
it may not burn up before it hits the ground. It comes
smashing into the earth, a white-hot lump that slowly
cools off. Then we call it a meteorite — a chunk of
metal, or metal mixed with rock, that has come to
earth from outer space.
262

Most meteorites burn away until very little is left of

them. But some, that were huge to start with, still

weigh many tons. And, several times, the earth has

been struck by enormous meteorites that dug huge
craters several miles (kilometers) wide and hundreds of
feet (meters) deep.
Most meteoroids that strike the earth and other
This meteorite is
planets are probably pieces of asteroids that have been
about four feet
(1 .2 meters) knocked out of their orbits. Others are probably parts
wide and weighs of comets.
3,275 pounds
(1,474 kilograms).

the great Meteor Crater of Arizona

Long ago, a giant meteorite crashed into the

earth and made this crater. The crater is
about 4,150 feet (1,265 meters) across and
570 feet (174 meters) deep.
J
A "star" with a tail

Night after night, a long, shining streak hung in the

sky. It looked like a big, bright star with a glowing tail.

Each night it seemed to grow bigger and brighter.

People were terrified. "It's the end of the world," they
wailed.
For thousands of years, whenever a comet appeared in

the sky, people were afraid of it. Now we know that

comets are just part of the sun's family. There are many
billions of them, going around and around the sun, just
as the planets do. Sometimes a comet's path brings it

close to the earth, so that it appears as a long, glowing-

streak in the night sky.
Most comets are balls of frozen gas, like snow, mixed
with dust. The comet does not have a tail until it gets
near the sun. Then, the sun's heat melts some of the
frozen gas, and gas and dust stream off into space,
forming the tail. The tail glows because sunlight shines
on the gas and dust and also releases energy from the
gas.
The center of a comet's icy head may be about ten
miles (16 kilometers) wide. It is surrounded by a cloud of
gas as much as a million miles (1,600,000 kilometers)
wide. A comet's tail may be as much as a hundred million
miles (160,000,000 kilometers) long.
Halley's Cornel seen trom the earth, New Mexico
 /\ A A
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 Planets, Stars, and Galaxies |
267

Why do stars twinkle?

The sun and its family of planets, asteroids,
meteoroids, and comets are like tiny specks of dust
floating in a gigantic ocean. The endless ocean of space
also contains countless billions of other "specks"
—the stars.

Stars shine with a steady glow, just as the sun does.

But they seem to twinkle. Why? Because, when the
light from stars reaches our atmosphere, it gets
bent, several times, by layers of moving air.

Five of the "stars" we see in the sky at night

are really other planets in our solar system. They shine
because they reflect sunlight. But most of the stars
are other suns, like our sun, that shine with light
of their own. These stars are trillions and trillions of

miles (kilometers) away from us.

The nearest star to us is so far that it takes four
years for its light to reach us. And light travels at
the tremendous speed of 186,282 miles (299,792
kilometers) per second. Some stars are so far that
it takes their light thousands, or even millions, of years
to reach us! A twinkle of light that you see in the sky
tonight may have been given off when dinosaurs
lived on earth!
How many stars are there? We don't know exactly,
but scientists believe there are billions and billions-
more stars than there are grains of sand on all the
beaches of the world!
Children sometimes wonder where stars go in the
daytime. They don't "go" anywhere, of course. They're
still there. It's just that our daytime sky is so bright
we can't see the stars.
268

Star pictures

On a clear night, you may see thousands of twinkling

stars. They seem to be scattered helter-skelter all over
the sky. But if you look carefully, you will see that
groups of stars seem to form shapes.
Long ago, people found that, with a little
imagination, each of these star groups looked like a
picture of something. One group of stars seemed to
look like a hunter with a club, holding the body of an
animal he had killed. Another group of stars made a
picture that was like a flying swan, with its long neck
stretched out and its wings spread. Other star groups
were like pictures of a crab, a bull's head, a dragon, a
man shooting a bow, and many other creatures and
objects.
The star pictures were named after the things they
looked like. By knowing the shape of each star picture,
and its position in the sky, sailors of long ago could
find their way across the sea. If a ship were blown off
course by a storm, the captain had only to look at the
star pictures to find the right direction again. Today,
amateur astronomers still use these star pictures, called
constellations, to locate the stars they want to study.
Planets, Stars, and Galaxies 269

the constellation of Orion

Long ago, people thought that

groups of stars looked like

pictures of creatures or objects.

Each star group was named after

the thing it seemed to look like.

These star groups are called

constellations. This constellation
is Orion the Hunter.
270

Finding constellations

Do you live in the Northern Hemisphere — say, in

the United States, Canada, Great Britain, or Japan?

Then, during most of the year you will be able to see
the constellationsshown on the star chart on page 271.
Do you live in the Southern Hemisphere in Australia, —
New Zealand, or South Africa? If so, during most of
the year you will be able to see the constellations
shown on the star chart on page 273. And, if you live

in the southern United States, Hawaii, or northern

Australia, you'll sometimes be able to see some of the
constellations on both star charts.
On the charts, the stars in each constellation are
joined together with lines to show the shape of the
constellation. If you know the shape of a constellation,

and where to look for it in the sky, you can usually find

it without much trouble.

To use the charts, take this book outdoors at about
nine o'clock, on a clear, moonless night. Stand where
you can see as much of the sky as possible. If you live

in the Northern Hemisphere, face north. In the

Southern Hemisphere, face south.
To see the chart, you'll need a flashlight. But cover
the light with red cellophane. Otherwise, the light will
dazzle your eyes and make it hard for you to see the
stars when you look up at the sky.
The constellations move into a different part of the

sky each month. So, around the outside of each chart

are the names of the months. Hold the book so that
the name of the right month is pointed at your chest.
Then the chart will show where the constellations will
be when you look up at the sky.
 Planets, Stars, and Galaxies 271

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cygnus;

DRACO

«i

pi
URSA CEPHEUS
MINOR
Big Dipper

CASSIOPEIA
: pointers

URSA MAJOR

• PERSEUS
Capella ,

AURIGA

AUGn jUtf
ST
272

For example, in the Northern Hemisphere, in May,

the group of stars Americans call the Big Dipper and
the British call the Plough will be straight ahead of
you, high in the sky. In the Southern Hemisphere, in
June, the constellation called Crux will be straight
ahead of you, close to the horizon.

On the charts, each constellation has its Latin name.

Some of the names are based on what people thousands
of years ago thought the constellation looked like.

For example, in the Northern Hemisphere there's a

That means "Dragon."
constellation called Draco.
Ursa Major means "Great Bear." Ursa Minor means
"Little Bear," though we usually call this constellation
the Little Dipper. Cygnus means "Swan" and Auriga
is "the charioteer." Cepheus was a king, and Cassiopeia
was a queen. Perseus was a storybook hero who killed

a monster and saved a princess.

In the Southern Hemisphere, there is a famous
constellation called Crux, which means "cross." It

is better known as the Southern Cross. Triangulum

Australe means "Southern Triangle." Musca is "Fly,"
Pavo is "Peacock," and Grus is "Crane." Vela is the
"sail" of a ship, and Carina is the ship's "keel," or
bottom.
The charts also show a few of the brightest stars,

such as Vega and Canopus.

If you live in or near a city, you may not be able
to see all of the stars or constellations because of the
city lights. But you will nearly always be able to see
the brightest stars and some of the constellations.
 Planets, Stars, and Galaxies 273

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TRIANGULUM —
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Achernar
• Beta Centauri
MUSCA

CRUX &
False Cross
Canopus

CARINA

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274 I Planets, Stars, and Galaxies

Exploding stars!

Nearly a thousand years ago, in the year 1054, a

new star suddenly appeared in the sky. It was
tremendously bright — so bright it could be seen even
in daytime. For two years, the strange new star
glowed in the sky, day and night. Then, it slowly
began to fade away. And, after a time, it disappeared.
Where had this bright new star come from? And
what became of it?

Actually, it wasn't a new star at all. It was a star

that had exploded.
Certain kinds of stars sometimes do explode. A kind
of small star called a white dwarf star may suddenly
flare up and become much, much brighter. Such an
explosion is called a nova, which means "new," because
it looks like a bright new star appearing in the sky.
But after a time the brightness fades away. The star
becomes no blighter than it was before it exploded.
When a very large star called a supergiant begins to
die, it, too, explodes. But this is a tremendous
explosion that destroys the star. The explosion sends a
gigantic cloud of glowing gas rushing out into space,
and the once-giant star suddenly becomes a little white
dwarf star. This kind of explosion is called a

supernova. A star that becomes a supernova may

become a billion times brighter. It was the light of a

supernova that was seen in the sky in 1054.

 »#
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276 Planets, Stars, and Galaxies

Misty shapes in space

A crab — a ring — a veil. These are some of the
shapes taken by giant clouds of gas and dust, called
nebulas, in space. The word nebula means "mist."

Some nebulas are the remains of stars that exploded

long ago. A ring nebula is a shell of gas that surrounds
a star, and looks like a ring from a distance. It is

caused by an explosion that blew away part of the star.

the Great Nebula

the Ring Nebula

Milky Way Galaxy

Our sun is part of a gigantic cloud of stars called the Milky Way Galaxy.

The Milky Way

On a clear summer night you can sometimes see a
bright haze in part of the sky. This haze is called the
Milky Way. It looks like a gigantic cloud of stars, close
together. Actually, the stars are many trillions of

miles (kilometers) apart. But there are so many of

them, they look like a glowing cloud.

The Milky Way is part of an even bigger cloud of
stars. This star cloud is shaped like a pancake with a
bulge in the middle. It contains more than 100 billion
 Planets, Stars, and Galaxies 279

stars. This huge mass of stars is called a galaxy —the

Milky Way Galaxy.
Our sun is one of the stars in this galaxy. The sun is

far out near the pancake's edge. We cannot see all the
way to the bulging center. Clouds of gas and dust, like

thick fog, block our view.

Just as the earth moves around the sun, the sun and
other stars move around the center of the galaxy. But
the galaxy is so enormous, and the sun is so far from its

center, that it takes the sun about 225 million years to

go all the way around!

the Milky Way

The glowing cloud we call the Milky Way is made up of billions of

stars that are trillions of miles (kilometers) apart. The white line in the

photograph is the track of an artificial satellite circling the earth.

280 Planets, Stars, and Galaxies

Other galaxies

Our galaxy, the Milky Way, has more than a

hundred billion stars. But it is not the only such
"cloud" of stars in space. There are at least a billion
other galaxies, and probably more, and each of them
also contains many billions of stars.

the Great galaxy

the Whirlpool galaxy
282 Planets, Stars, and Galaxies

Waves from space

Right this minute you're being hit by "bullets" from
outer space!
Space is full of waves. These aren't the kind of

waves you see on an ocean, of course. They are waves

of radiation. Radiation is streams of tiny, tiny bits of
atoms. These particles are so small you couldn't see
them even with the most powerful microscope. They
travel at tremendous speed— 186,282 miles (299,792
kilometers) per second. They are like little bullets.
When they reach earth, some of them go zipping right
through you, without you even knowing it
Radiation is given off by most things in space stars, —
quasars, planets, and the huge clouds of gas and dust
called nebulae. Radiation comes to earth in the form
of light, heat, radio waves, and what we call X rays,

cosmic rays, and gamma rays.

Earth's atmosphere shuts some of these things out.

Scientists think there is also a kind of "wall" in our

solar system that shuts out others. This is a good

thing, because if too many of some of these particles

entered peoples' bodies, they could cause sickness.

Even though the particles are so small that the

waves are invisible, scientists have many machines

that can find different kinds of radiation and tell

where it comes from.

this radio telescope can locate waves from space
284

Sky "fireworks"
People who live far enough north or far

enough south are often treated to a giant

"fireworks" display on clear nights. Great
sheets of light seem to hang in the sky,

rippling and wavering like curtains in a

breeze. The light flickers with colors
frosty-white, pale green, and pink.
These lights are inside the earth's

atmosphere, but what causes them comes

through space from the sun. Whenever
the sun has many sunspots, it shoots out
great numbers of tiny particles of energy
into space. Many of these particles come
to earth.
Near the earth's North and South poles
there are magnetic poles. These north
and south magnetic poles are like the
ends of a big magnet. They attract the
particles of energy from the sun. The
particles collide with other particles in the
earth's atmosphere. This makes them
glow, filling the sky with shimmering,
shivering light.
In the Northern Hemisphere, these sky
"fireworks" are called the aurora borealis,
which means "northern lights." In the

Southern Hemisphere, they are called the

aurora australis, meaning "southern
lights."
Planets, Stars, and Galaxies 285
 287

Where
in the
World?
the earth as seen from space
 Where in the World? I
289

The big, blue marble

The earth looks like a big, blue marble to astronauts

flying in outer space. It's easy for them to see the
round shape of the earth because the astronauts are so
far away. But how can you see the shape of the earth
while you're standing on it?

Look at a globe. A globe is a model of the earth. It

shows you mountains, oceans, lakes, rivers, deserts,
grasslands, and forests. Most globes even tilt, just like
the real earth.
A globe shows the earth as it really is-— round. And
it shows the true shapes of the continents. But with a
globe, you see only a part of the earth at one time. To
see places on the other side, you must turn the globe.
If you want to see the whole earth at one time, you
have to look at a map. But a map won't show you the
earth as it really Mapmakers squeeze and stretch
is.

parts of the world when they draw them on a flat map.

So, a globe is the best way to see the shape of the

earth — unless you have a spaceship.

a globe is a model of the earth

i-"^

J^L v^c

photographs taken from airplanes help mapmakers

Places on paper
You can't put a globe in your pocket. A big, round
globe is too bulky to carry from place to place. That's
why there are maps. Travelers can easily fold paper
maps to take with them.
Besides being easy to carry, maps can show a small
part of the earth in detail. If you are looking for a

small town you can find it on a

or a street in a city,
map but not on a globe. There isn't room on a globe
for such places — even a very large globe.
map made from the photograph on the opposite page

Maps make the earth look flat. They are drawn as if

you are high up, looking straight down on the land.

When you look at a map, you can see what's beyond a
forest or on the other side of a mountain.
How do the people who make maps know so much?
They learn about the earth in many ways. But the
best way is to use photographs taken from an airplane
or satellite. The photographs are put together like
pieces of a puzzle. Using the photographs as a guide,
the —
mapmakers who are called cartographers draw —
their maps. They pick only the places that may be
important to people who will use the maps.
a meteorologist using a
computer map to forecast
the weather

a pilot and weather

forecaster using flight
charts and weather maps
a family using a road map to plan their vacation

All kinds of maps

Maps show you all kinds of things about the earth
and space. The kind of map you probably know best is

a road map. This kind of map shows roads, cities,

rivers, and important places. You use road maps when

you go on auto trips.

Sailors and airplane pilots also use a sort of "road

map" called a chart. Their charts show the "highways"
of the oceans and skies.
In school, you use maps that show countries, states,
provinces, cities, and other important places. You also

might use a map that shows how rough or smooth the

land is. One kind of map has a raised, bumpy surface.
You can see and even feel the earth's hills and valleys!
There are maps that show where people live. Other
kinds of maps show the weather, crops, or events of
history. There are even maps of the moon, the stars,

and the planet Mars!

294

Forest
 Where in the World? 295

Map language
Follow the Yellow Brick Road!
If you were in the Land of Oz, the

Yellow Brick Road would lead you to

Emerald City. But in real life there are

no Yellow Brick Roads to guide us to

where we want to go. So, we use maps.
And mapmakers use symbols and colors
to show us what we want to know.
Map symbols stand for real things on
the surface of the earth. Most of the

symbols are simple and quite easy to

understand. They are usually explained
in a box near a corner of the map. And
the colors help. Man-made things — such
as highways —are usually red or black
lines. The wider the line, the bigger the
highway. Crossed lines stand for railroad
tracks, and dots stand for cities. A star
or dot inside a circle means a capital city.
And to find an airport, look for a tiny

drawing of an airplane.
Water is shown in shades of blue, so
those squiggly blue lines show rivers.
Sometimes color is used to show the
height, or elevation, of the land. Fairly
low land might be colored green. High
mountains may be dark brown.
The next time you see a map, look
again. You'll be surprised to find out
how symbols and colors help mapmakers
show a lot on a very small map.
296

How far is it?

A map may be millions of times smaller than the real

land it pictures. So how can you find out how far it

is from one place to another?

To find out, you use a "measuring stick" called a
scale. Scale means that a certain distance on a map
stands for an actual distance on the earth's surface.
Map scales are shown in three different ways. One
kind of scale is a straight line on which distances are
marked. Each mark stands for a certain number of

miles or kilometers. To find the actual distance between

two places, measure the distance between them on the
map. To do up the two places on the edge of
this, line

a piece of paper. Make a mark for each place. Then,

move the paper down to the scale. Line up one mark
with the on the scale and read the distance opposite
the other mark.
Another kind of scale says that so many inches or
centimeters equal so many miles or kilometers. For
example, the scale might read: 1 inch = 10 miles, or
perhaps 1 centimeter = 20 kilometers. With a ruler,
measure the distance between two places on the map.
Then, multiply inches by 10 to get miles or centimeters
by 20 to get kilometers.
Still another kind of scale is shown as a fraction. If

the map has 1 50,000 as its scale, then 1 unit of

measurement on the map is 50,000 times larger on the
surface of the earth. With this kind of scale, 1 inch or

1 centimeter on the map would equal 50,000 inches or

centimeters on the earth.
 Where in the Work]'.' 297

measuring distance on a map

Find the distance from Paris

to Vienna by using a piece
of paper and the scale from
,-""= the map below. About how far
is it from Berlin to Madrid, or
from Dublin to Athens?

, Copenrtager

z.- '
Warsaw *

--------

--••;

.'.' = :-:

-^-h' :

: -:: r.: v.: a;: -.:: -.:: ".'- -v. v.: :•:: -_-£-*-=
298

pocket compass

Which way?
Which way are you going? A compass can tell you. A
compass is a box with a magnetic pointer or needle
that turns. The marked end of the needle always points
north. Why? Because it is pulled by a larger
magnet — the earth. The earth is a giant magnet. One
end is near the North Pole and the other end is near
the South Pole. And the north-seeking end of a
magnetic needle always points toward the north
magnetic pole.
If you want to go east, hold the compass level until

the needle stops moving. Then turn the compass case

until N, or north, is under the marked end of the
needle. Face north and turn to your right — that's east.

You can use the sun as a direction-finder, too. The

sun rises close to the east and sets close to the west.
Face the rising sun and lift your left arm straight out

from your side. You will be pointing nearly north. If

you face the setting sun, your left arm will be pointing

nearly south. And, at about noon, if you live in the

Northern Hemisphere (North America, Europe, or
Asia), your shadow will point north. If you live in the
Southern Hemisphere (Australia, South America, or
southern Africa), your shadow will point south.
 Where in the World? 299

On a clear night, you can use the stars to find north.

In the Northern Hemisphere, look for the Big Dipper.
Find the two pointer stars in the side of the cup. These
two stars always point to the North Star, at the tip of

the handle of the Little Dipper. The North Star is

always in the northern part of the sky, directly over

the North Pole.
In the Southern Hemisphere, look for the Southern
Cross. The two stars in the longer bar always point
south.

Things needed to make a compass

magnet
straight pin or needle

piece of cork about 1 inch (1 centimeter)

wide by A inch (1 centimeter) thick
1

bowl or saucer of water

Rub one end of the pin along bowl of water. At first, the pin
the magnet about twelve times. and cork will swing around.
Rub in one direction only. Don't Then the pin will point steadily
rub back and forth. Lift the pin in one direction. It points along
up each time. the magnetic line between the
Place the pin on the cork. earth's North and South poles.
Gently place the cork in the
300 Where in the World?

Lines around the world

Look at a globe or a map of the world. Have you

ever wondered why there are so many crisscross lines?
parallels of latitude There are no lines on the earth, so why put lines on
globes and maps?
The lines are put there to make it easy to find
places. The lines are like city streets. When two friends

meet at the corner of Oak and Main, they are meeting

where two streets cross. On a globe or map, the
east-west lines cross the north-south lines just like
streets. Every place on earth can be found at or near
meridians of longitude
where two of the lines cross.

The east-west lines measure distance north or south

of the equator. This is called latitude. Because the
lines are parallel — always the same distance apart—we
call them parallels of latitude. Latitude is measured
in units called degrees. The symbol after each number
is a degree sign. Latitude is always given as so many
degrees north or south of the equator.
The north-south lines measure degrees east and west.
We call this longitude. The lines are called meridians.

The starting point is a line called the prime meridian.

This line passes through Great Britain. Longitude is

given as so many degrees east or west of this line.

Latitude and longitude is one way to find a place.

Another way is used on small area maps, such as road
maps. Numbers and letters are around the edges of a

road map. Lines drawn from the letters cross other

lines drawn from the numbers. Such a map will have a
list of the places shown. After each place name, there
is a symbol, such as C4. Look at the map and you
will find the place near where the lines C and 4 cross.
Treasure Hunt
treasure latitude 2° north

Find the four treasures by ship longitude 2° east

using the latitude and buried latitude 2° south

treasure longitude 0°
longitude given for each one.
Work out for yourself the pieces of latitude 1° north
eight longitude 2° west
latitude and longitude of

places shown on the map. golden latitude 0°

idol longitude 1° west
302

The sun's boundary lines

Do you know why most globes are tilted on their

stands? It's because the earth is tilted. Because of this
tilt, different places on earth get different amounts of

sunlight. Special lines on globes and maps mark the

edges of these different places.
Halfway between the North and South poles is the
imaginary line we call the equator. At the equator,
it is always daylight for twelve hours each day. So
days and nights are the same length all year long.
North of the equator is an imaginary line called the

Tropic of Cancer. South of the equator is another line

called the Tropic of Capricorn. Both lines are named
for star constellations. Once a year the sun is directly

over the Tropic of Cancer. That's the first day of

first day of summer in first day of summer in

the Northern Hemisphere the Southern Hemisphere

Arctic Circle

Tropic of
Tropic of
Cancer
Cancer

sun
directly
-sun
overhead
directly
overhead

Tropic of
Tropic of Capricorn
Capricorn

Antarctic Circle Antarctic Circle

 Where in the World? 303

It's a Fact

At the North Pole, the sun

never sets from about
March 20 to about
September 23.

c-

1
-"VJ

*
J-

summer in the Northern Hemisphere. Once a year, the

sun is directly over the Tropic of Capricorn. That's the
first day of summer in the Southern Hemisphere.
Near the North and South poles are two other
imaginary lines — the Arctic Circle and the Antarctic
Circle. In the region between the Tropic of Cancer and
the Arctic Circle, the sun always shines clown at a
slant. The same thing is true in the region between the
Antarctic Circle and the Tropic of Capricorn. So in
these regions, days are long during part of the year
and short during another part of the year.
North of the Arctic Circle is a region sometimes
called the "Land of the Midnight Sun." In the summer,
there are days when the sun never sets. You can go
out at midnight and see the sun! But in the winter,
there are days when the sun never rises. The same
thing is true south of the Antarctic Circle.
 .",();-»

People
Who Study
the World
and Space
 ¥
geologist chippingoff a
rock sample for laboratory study
 People Who Study the World and Space |
307

Learning about the earth

Who wants to study rocks? Geologists do.

Geologists are scientists who "read" rocks as though
they were history books. Rocks have a history of their
own. They show geologists what the earth was like

millions of years ago, how it has changed since then,

and how it is still changing. By studying rocks,
geologists learn where rivers once flowed — where
volcanoes once erupted — and where plants and animals
once lived.

Many geologists travel all over the world. They

explore mountains, swamps, deserts, and even the
bottom of the ocean. As geologists learn more about
the structure of the earth, the search for oil, coal,

and other sources of energy becomes easier. Valuable

minerals, such as gold, tin, and copper, are found by
geologists, too.

Before geologists become geologists they may be

"rock hounds." Rock hounds collect rocks as a hobby.
But if rock hounds become geologists, they do much
more than study rocks. Geologists study everything
about the earth. That is what the word geology means.
It comes from two Greek words, ge, which means
"earth" and logos, which means "study." And now
geologists study rocks brought back from the moon
308 |
People Who Study the World and Space

Learning about
prehistoric life

Scaly dinosaurs and flying reptiles

disappeared from the earth about
sixty-five million years ago — long before
there were people. Yet there are pictures
of these animals in books. How do we
know what these prehistoric animals
looked like if no one ever saw a live searching for fossils

dinosaur or a flying reptile?

Scientists called paleontologists tell
us what the plants and animals of
long ago were like. They examine
fossils — the remains of plants and
animals left in stone and other places.
These include fossil bones, teeth,
footprints, and leafprints. From such
fossils, paleontologists can tell a great
deal about living things of the past
how big they were,what they looked
like, how they walked, and even what
food they probably ate!
Where are fossils found? The search
for fossils goes on just about everywhere.
Fossils have been uncovered on high
mountaintops, under layers of ice, in

steep cliffs along rivers, and in coal

mines. The oldest fossils ever found are
simple plants that lived more than three
billion years ago.

This paleontologist is looking at the

fossil skeleton of a mammoth.
 fossil insect

This insect was trapped in tree

sap millions of years ago.

When the sap hardened, the
insect was sealed in forever.

fc -.-rf*
J
w

7.

t/

m
310

Cave scientists

Watch your head — there's a stalactite! Oops, don't

trip over the stalagmite! Where are you? In a cave!
Scientists who study caves are called speleologists.
Most caves are dark, slippery tunnels of rock and
water. Exploring them can be dangerous. So speleologists

wear protective clothing and headlamps. And they

carry rope and other tools. These scientists want to
find out about the changes a cave goes through. They
alsowant to know how long each change lasts and
what happens to a cave during this time.
Some caves are like underground art museums. The
limestone formations look like beautiful sculptures.
And man's earliest art —painted more than twenty-five
thousand years ago — has been found on cave walls.
Where is the deepest cave? No one knows. But in a
cave in France, explorers climbed down almost three
thousand feet (910 meters).
 People Who Study the World and Space |
31]

cave scientists at work

A group of cave explorers (left) crawl

through a narrow underground tunnel.
A scientist (below) makes tests in a
limestone cave in Mexico.
312 People Who Study the World and Space

Watching for earthquakes

Earthquakes happen all the time. We don't feel most
of them. They are just small shakes in the earth. But
some earthquakes make the ground tremble, rattle
dishes, and even cause buildings to shake. And a few

earthquakes smash and crumple buildings.

Seismologists are scientists who study earthquakes.
Seismologists can't go underground to watch the rocks
push, snap, and break. Instead, seismologists watch
instruments called seismographs. These instruments
help keep track of earthquakes all over the world
even the quakes we can't feel.

Seismographs are usually set on solid rock or inside

vaults. There, they do not pick up vibrations caused

by man-made But when an earthquake makes
things.
the earth shake, tremble, and shiver, it also moves a
pen in the seismograph. The pen draws squiggly lines
on a roll of paper.
Scientists use seismographs in groups of three. This
way they can measure the east- west, north-south, and
up-and-down ground motions of the earth.

A few times, seismologists have been able to predict

earthquakes. But there much to learn about
is still

what causes earthquakes and when they will happen.

seismologist checking a seismograph

A seismograph is used to record movements of

the earth near the top of Mount Asama in Japan.

314

volcanologist collecting samples of hot lava

 People Who Study the World and Space

Volcano watchers
The ground shakes and quivers. Deep
in the earth there is a roaring rumble.
Suddenly, there is a giant explosion! A
cloud of steam, mixed with dust and
chunks of rocks, shoots out of the top

of the volcano. A river of hot, boiling

lava — melted rock—pours out of cracks.
The lava flows down the sides of the
volcano, burning everything in its path.
After the lava cools, scientists called
volcanologists may visit the volcano
to study it. Someday, scientists hope to
forecast volcanic eruptions. So, to learn
more, they climb to the top of the
volcano to collect gases. They draw the
gas from the boiling bubbles inside.
Changes in the gas warn volcanologists
when a volcano might erupt.
Several machines help scientists watch
volcanoes, too. A tiltmeter measures the
slant of the earth's surface. When the
slant changes around a volcano, it's a
sign that the volcano could erupt. A
seismograph is used, also, to show any
warning rumbles, shakes, and quivers in

the earth. Being a volcanologist means

plenty of watching and waiting.

4
 I

living under water

An oceanographer uses a device called a

sonar to locate underwater sounds. Behind
her is the underwater house she stays in.
 People Who Study the World and Space 317

Learning about the sea

How long can you hold your breath under water?

A few seconds? A minute? Whatever the length of
time, you can't stay under water very long.
But scientists called oceanographers often swim
under water for hours. Some oceanographers even live

beneath the ocean's surface for months at a time!

Oceanographers use air tanks, diving suits, or even
small submarines while under water. And when
oceanographers stay under water for days at a time,
they live in a canlike house right on the ocean floor.

There, scientists spend hours outside their underwater

shelter studying everything around them.
There are many kinds of oceanographers. Some make
maps of the rocky ocean floors. Other sea scientists
map the direction and strength of the moving water.
Still other oceanographers study the plants and animals
that live in the ocean.

sampling the ocean bottom

Japanese oceanographers check

and bottle samples of mud and
sand brought up from the ocean
floor. They will study the mud
to find out what's in it.
318

Watching the weather

Everyone is a weather watcher. But no one knows
for surewhat the weather will be like tomorrow or
—
next week not even meteorologists.
Meteorologists are scientists who study the weather
and try to forecast it. Sometimes their forecasts are

wrong because weather conditions can change quickly.

In a way, meteorologists are like detectives. They
look for all kinds of clues to help them discover what
kind of weather is coming. They check the wind for
speed and direction. They keep records of temperature,
air pressure, and the amount of water in the air. They
follow the progress of storms. With radar, they can
find approaching storms as far away as two hundred
miles (320 kilometers).
Meteorologists also have "weather spies" in the
sky. One such spy is a large, gas-filled balloon. The
balloon carries instruments high into the sky. Wind
speed, temperature, and other weather conditions are
automatically radioed to the weather stations below.
The highest sky spies are weather satellites. These
satellites circle the earth and photograph cloud cover
and any gathering storms. The pictures are then
radioed to earth.
Meteorologists gather weather reports from all over
the world. Using this information, they draw weather
maps. With the help of computers, forecasts are made
and sent to weather stations and then on to you.
Will it rain tonight? Will the sun shine tomorrow?
Meteorologists try to let you know ahead of time.
measuring weather

This gas-filled balloon carries instruments

to measure the weather.

studying weather

A meteorologist uses a bank of computers

to study weather information.
320

Studying the stars

What is the shape of the universe?

Why do stars sometimes explode? Is there

life on other planets? Scientists called

astronomers and astrophysicists try to
answer these and other questions.
Most astronomers do much of their
work at places called observatories.
There, they use telescopic cameras to
r&BBS1C«:
take photographs of stars. They study
hundreds of photographs to find out the
movements of stars and to look for new
objects in space. With mathematics, they
figure out how far away stars are and
how fast they move.
Astronomers also listen to sounds that
come from space. To do this, they use
radio telescopes that pick up radio waves.
The astronomers try to find where the
sounds are coming from and what makes
them.
Astrophysicists want to know what the
things in space are made of. For example,
astronomer, Chile
they can by the different colors in
tell

the light of a star what chemicals are in

the star. They also study other planets

to try to find what they are From
like.

the work of all these space scientists, we

are learning more and more about the

amazing universe in which we live.

How far away are the stars? How

many stars are there?
Astronomers use telescopes,
special instruments, and math to
answer questions like these.
 People Who Study the World and Space |
.".21

Hubble Space Telescope

Hubble
artist's idea of
Space Telescope in orbit
around the earth
322

Books to Read
If you like to read about the world and Mars by Seymour Simon (Morrow, 1987)
space, you'll find a wide variety of books Read about and see amazing photographs
to read and enjoy.A few of them are of the earth's closest neighbors in the
listed below. Your school or your public solar system. You can also find books
library will have many others. about other planets and the sun by the
same author.

One Day in the Desert by Jean

Ages 5 to 8 Craighead George (Crowell, 1983)
Air Is All Around You Revised Edition Deserts are dry; deserts are sandy;
deserts can be very hot and very cold.
by Franklyn M. Branley (Crowell, 1986)
You can't see it, but air is everywhere, How do plants and animals live there?
even in some places that will surprise
Read about daily life in the desert in this
book.
you.

The Big Dipper and You by E. C.

My Place in Space by Robin and Sally
Hirst (Orchard Books, 1988)
Krupp (Morrow, 1989)
If you ride in a spaceship that travels as
In this picture book, Henry and his sister
Rosie ride the bus home. The bus driver
fast as the Voyager, it would take you 10
billion years to get to the Big Dipper. asksHenry if he knows where he lives.
This book will get you there much faster.
Henry knows more than his address; he
knows the exact location in the universe.
Comets by Ruth Radlauer and Charles
H. Stembridge, Ph.D. (Childrens Press,
The Sun: Our Neighborhood Star by
David J. Darling (Dillon Press, 1984)
1984)
This book answers questions that you
What are comets? Where do they come
might have about the sun and its
from? This book is full of astounding
information.
connection to the earth. It also tells when
the eclipses of the sun occur from 1984 to
1999.
The Great Lakes by Kathy Henderson
(Childrens Press, 1989)
Did you know that more standing fresh
Why Doesn't the Earth Fall Up? by
water can be found in the Great Lakes Vicki Cobb (Lodestar, 1989)

than anywhere else in the world? That's Find out how the force of gravity keeps
things on earth from floating off into
one-fifth of all the earth's standing fresh
space.
water. Read this book to find out more
about the five Great Lakes.
Ages 9 to 12
The Magic School Bus Inside the
Earth by Joanna Cole (Scholastic, 1987) The Arctic and Antarctic by Cass R.
The magic school bus goes on a field trip Sandak (Franklin Watts, 1987)
inside the earth. Ride along to learn how Explore the polar regions at the top and
the earth formed and find out about bottom of the earth, around the North
different kinds of rocks. and South poles.
 Books to Read 323

Earthquakes: Nature in Motion by My FirstBook of Space by Robert A.

rlershell H. Nixon and .loan Lowery Bell (Simon & Schuster, 1985)
Nixon (Dodd, Mead, L981) This informative book about our universe
Discover why the earth quakes, the is illustrated with NASA photographs and

signalswe look for to predict earthquakes, art.

and even how we might "turn them off"!

101 Questions and Answers About the

Earth Songs by Myra Conn Livingston
Universe by Roy A. Gallant
(Holiday, 1986)
(Macmillan, 1984)
These poems celebrate the earth its — As the director of a planetarium, the
continents, hills, forests, and seas. They
author spent a lot of time talking to
are enhanced by Leonard Everett Fisher's
children. In this book, he answers
beautiful paintings. Also, look for Space
questions that children have asked him
Songs by the same author.
most frequently.

")() Simple Things Kids Can Do to Save

the Earth by The Earth Works Group Satellites and Space Stations by Moira
(Andrews & McMeel, 1990) Butterfield (London, Usborne, 1985)
I .earn what you can do to make the earth Satellites play a vital role in world
a healthy place for people everywhere. communications, astronomy, and many
other areas. Learn what space stations
The Galaxies by David Darling (Dillon, are and how people work and live in
1985) them.
This book tells what galaxies are and how
they were formed.
Science Activities for Children by
Willard J. Jacobson and Abby B.
How Did We Find Out About
Bergman (Prentice-Hall, 1983)
Volcanoes? by Isaac Asimov (Walker, These activities are a fun way to help you
1981)
understand some important ideas in
The author tells how people have viewed
science. Several chapters contain activities
volcanoes from ancient times to the
related to our world and space.
present. He even tells about volcanoes
that are not on earth.
Solids, Liquidsand Gases: From
Mountains by Keith Lye (Silver Burdett, Superconductors to the Ozone Layer
1986) by Melvin Berger (Putnam, 1989)
Are mountains alike? How are they
all
Gain a deeper understanding of the three
formed? Do they ever change? You may forms of matter by performing scientific
be surprised by the answers to these and experiments.
other questions.
Space Laboratories by Gregory Vogt
Mountains and Earth Movement by Ian (Franklin Watts, 1987)
Bain (Bookwright Press, 1984) Laboratories in space help us understand
Learn why the earth moves and what our universe. Learn about past, present,
happens when parts of the earth move. and future space laboratories.
324

New Words
Here are some of the words you have met in this
book. Many them may be new to you. Others
of
are just hard to pronounce. Since you'll see them
again, they're good words to know. Next to each
word you will see how to say the word: ammonia
(uh MOHN yuh). The part shown in capital letters
is said a little more loudly than the rest of the

word. Under each word are one or two sentences

that tell what the word means.

ammonia (uh MOHN yuh) bauxite (BAWK syte or BOH zyt)

Ammonia is a colorless gas. It is Bauxite is a brownish or grayish
often dissolved in water and used for mineral. Its ore is the chief source of
cleaning. aluminum.
anemometer (an uh MAHM uh tuhr) calcite (KAL syt)
An anemometer is an instrument that Calcite is a mineral. It is the
measures the speed of the wind. chief substance in limestone, chalk,
asteroid (AS tuh royd) and marble.
An asteroid one of many small
is carbon dioxide
planets that revolve around the sun. (KAHR buhn dy AHK syd)
astrophysicist (as troh FIHZ uh sihst) Carbon dioxide is a colorless,
An astronomer who studies the odorless gas that is in the earth's
physical and chemical characteristics atmosphere.
of planets and stars is called an carnotite (KAHR nuh tyt)
astrophysicist. Carnotite is a yellow-colored,
atmosphere (AT muh sfihr) powdery, radioactive mineral that
The atmosphere is all the air that is one of the sources of

surrounds the earth. uranium.

aurora australis cartographer (kahr TAHG ruh fuhr)
(aw RAWR uh aw STRAY lihs) A person who makes maps or charts
The aurora australis is bands of light is called a cartographer.
in the night sky in the Southern cassiterite (kuh SIHT uh ryt)
Hemisphere. Cassiterite is a mineral ore. It is the
aurora boreal is chief source of tin.
(aw RAWR uh bawr ee AL ihs) chromium (KROH mee uhm)
The aurora borealis is bands of light Chromium is a shiny, gray metal
in the night sky in the Northern that does not rust.
Hemisphere. cinnabar (SIHN uh bahr)
azurite (AZH yuh ryt) Cinnabar is a mineral. It is the chief
Azurite is a copper mineral that has source of mercury.
a blue color. It is used for jewelry. cirrocumulus (sihr oh KYOO myuh luhs)
basalt (BAS awlt or buh SAWLT) Cirrocumulus clouds are rows of
Basalt is a dark-colored rock that small, fleecy, white clouds, often
was once red-hot lava. called a "mackerel skv."
 New Words :!25

cirrus (SIHR uhs) erosion (ih ROH zhuhn)

A cirrus cloud is a thin, fleecy, white Erosion is the slow wearing away
cloud of ice crystals that forms at a of soil or rock.
high altitude fluorite (FLOO uh ryt)
cobalt (KOH hawlt) Fluorite is a mineral with a glassy
Cobalt is a metal often found with luster.
nickel and copper. fossil (PAHS uhl)
comet (KAHM iht) A the remains or traces of
fossil is

A comet is a bright object in space. an animal or plant that lived long-

It looks like a star with a tail. ago. A fossil may be a footprint, a
condensation trail bone, or the outline of a leaf.

(kahn dehn say shuhn trayl) gauge (gayj)

A condensation trail, or contrail. A gauge is a measuring instrument.
is stream of water droplets or
a Geiger counter (GY guhr KOWN tuhr)
ice crystals that can be seen The Geiger counter is an instrument
forming behind highflying aircraft in that detects radioactivity.
the upper atmosphere. geyser (GY zuhr or GY suhr)
constellation (kahn stub LAV shuhn) A geyser is a spring that shoots
A constellation is a group of stars up hot water and steam.
that appears to have special shape glacier (GLAY shuhr)
when viewed from the earth. A glacier is a huge mass of gritty
corundum (kuh RUHN duhm) ice that slides slowly over the land.
Corundum is a very hard mineral. graphite (GRAF yt)
Rubies and sapphires are kinds of Graphite is a soft, black mineral used
corundum. with clay to make the "lead" for
Crux (kruhks) pencils.
Crux, a Latin word that means halite (HAL yt or HAY ryt)

"cross," is a constellation in the Common table salt is the mineral

Southern Hemisphere. It is usually called halite.
called the Southern Cross. hematite (HEHM uh tyt or HEE muh tyt)
crystal (KRIHS tuhl) Hematite is iron ore that is
A crystal is something that has sometimes called blood ironstone
hardened into a shape that has because of its red color.
smooth, flat surfaces that meet in igneous (IHG nee uhs)
sharp edges and corners. Rock that was formed when it was
cumulonimbus heated to a liquid state is called
(kyoo myuh loh NIHM buhs) igneous rock. See also metamorphic;
Cumulonimbus is a heavy cloud mass sedimentary.
with high peaks: a thundercloud. indigo (IHX duh goh)
cumulus (KYOO myuh luhs) Indigo is a deep violet-blue color.
A cumulus cloud has a rounded top magma (MAG muh)
and a flat bottom. It is usually seen Magma is the hot, melted rock
in fail' weather. beneath the earth's crust.
detail (dih TAYL or DEE tayl) malachite (MAL uh kyt)
A detail is a picture of a small part Malachite is a green mineral.
of something. It is sometimes shown meridian (muh RIHD ee uhn)
larger than the whole thing. A meridian is an imaginary line
diatom (DY uh tahm) around the earth. Meridians meet
A diatom is a tiny water plant. at the North and South poles. We use
326

meridians to measure distance east or studies the plants and animals of

west. See also parallel. long ago.
metamorphic (meht uh MAWR fihk) parallel (PAR uh lehl)
Metamorphic means changed. A Lines that are parallel are the
metamorphic rock is one that has same distance apart everywhere.
been changed by heat and pressure. The imaginary lines circling the earth
See also igneous; sedimentary. above and below the equator are
meteor (MEE tee uhr) called parallels. We use these
A meteor is a chunk of metal or parallels to measure distance north or
stone (a meteoroid) that has entered south. See also meridian,
the earth's atmosphere from outer patina (PAT uh nuh)
space and is burning up from friction. Patina is a coating often found on
It is often called a shooting star. the surface of old bronze or copper.
meteorite (MEE tee uh ryt) petrified (PEHT ruh fyd)
A meteorite is a meteor that has Something that is petrified has
reached the earth without burning up. been changed into stone.
meteoroid (MEE tee uh roihd) petroleum (puh TROH lee uhm)
A meteoroid .is a chunk of rock that Petroleum is a dark, oily liquid found
is moving through space. in the earth. Gasoline and oil are

meteorologist (mee tee uh RAHL uh jihst) made from petroleum.

A meteorologist is a person who Polaris (poh LAIR ihs)
studies the atmosphere and its effect Polaris, the North Star, is in the
on weather. northern constellation Ursa Minor,
molecule (MAHL uh kyool) usually called the Little Dipper.
A the tiniest part into
molecule is Polaris is above the North Pole. It is

which any substance, such as water, used in the Northern Hemisphere to

can be divided without changing into find north.
something else. pulsar (PUHL sahr)
nebula (NEHB yuh luh) A pulsar is a very tiny star that
A nebula is a huge cloud of gas or sends out short, regular bursts of
dust in space. radio waves.
nimbostratus (nihm boh STRAY tuhs) pyrite (PY ryt)
Nimbostratus is a low, dark-gray Pyrite is a yellow mineral that looks
layer of rain or snow clouds. like gold.
nitrogen (NY truh juhn) quadruplet (KWAHD roo pliht)
Nitrogen is a gas that has no color, A quadruplet is any group or
odor, or taste. It makes up almost combination of four.
80 per cent of the air we breathe. quartz (kwawrts)
obsidian (ahb SIHD ee uhn) Quartz is a very hard mineral.
Obsidian is a hard, dark, glassy rock refinery (rih FY nuhr ee)
that forms when lava cools. A refinery is a place where metal,
oceanographer petroleum, or sugar is made as pure
(oh shuh NAHG ruh fuhr) as possible.
A person who studies the ocean and saltpeter (sawlt PEE tuhr)
the different kinds of ocean life is Saltpeter is a salty, white mineral
called an oceanographer. used in making gunpowder.
paleontologist satellite (SAT uh lyt)
(pay lee ahn TAHL uh jihst) A satellite is a natural or artificial
A paleontologist is a person who object that revolves around a planet.
 Wu Words 327

sedimentary (sehd uh MEHN tuhr ee) stalactite (stuh LAK tyt)

Anything that is sedimentary is made A stalactite an icicle-shaped
is

from sediment —
small bits of matter deposit of calcite hanging from
left by water, wind, or ice. Rocks the roof or sides of a cave.
formed from minerals that settle in stalagmite (stuh LAG myt)
this way are sedimentary rocks. Set A stalagmite is a deposit of calcite
also igneous; met amorphic. forming a stone column that rises up
seismograph (SYZ nnih graf) from the floor of a cave.
A seismograph is an instrument that titanium (ty TAY nee uhm)
measures and records movements in Titanium is a metal used in making
the earth, especially earthquakes. steel.
seismologist isyz MAHL uh jihst) turquoise (TUR koyz or TUR kwoyz)
A seismologist is a person who Turquoise is a blue-to-green
studies earthquakes and other gemstone.
movements of the earth. uranium (yu RAY nee uhm)
selenite (SEHL uh nyt) Uranium is a radioactive metal.
Selenite is a form of the mineral volcanologist
gypsum. It is used in making plaster (vahl kuhn NAHL uh jihst)

and cement. A scientist who studies volcanoes

sonar (SOH nahr) is called a volcanologist.
Sonar is an instrument that uses wulfenite (WUL fuh nyt)
sound waves to find the direction and Wulfenite is a mineral that contains
distance of objects under water. a metal used in making steel.
speleologist (spee lee AHL uh jihst) zircon (ZUR kahn)
A speleologist is a person skilled Zircon is a mineral often used as
in the studv of caves. a gem.
328

Illustration
acknowledgments

The publishers acknowledge the

of Chitdcraft gratefully
following artists, photographers, agencies, and corporations
for illustrations in this volume. Page numbers refer to two-

page spreads. The words "(left)," "(center)," "(top),"

"(bottom)," and "(right)" indicate position on the spread.
All illustrations are the exclusive property of the publishers
of Childcraft unless names are marked with an asterisk (*).

(top left) NASA *; (top right) Rare Coin Co ol America, 78-79: Childcraft photos
Chitdcraft photo; (center left) NASA '; (center right) 80-81 Field Museum of Natural History, Childcraft photo
Childcraft photo; (bottom left) James Conahan; (bottom 82-83: Erich Lessing. Magnum '

right) E S. Ross * 84-85; (left) Field Museum of Natural History, Childcraft photo,
4-5: James Conahan Robert Weldon, Gemological Institute of America *;

6-19: Herb Hernck Robert Weldon. Gemological Institute of America *, Field

20-21 James Conahan Museum of Natural History, Childcraft photo, Robert
22-23: George Suyeoka Weldon, Gemological Institute of America ', Jeffrey
24-25: Ray Atkeson, DPI '
Kurtzeman, (right) Field Museum of Natural History,
26-27: (left) Alan Band Associates *; (right) R N Mariscal, Childcraft photo, T Hammid, Gemological Institute of
"
Bruce Coleman Inc. America "; Childcraft photo; Childcraft photo; Robert
"
28-29 James Conahan Weldon, Gemological Institute of America
*
30-31 Paolo Koch, Rapho Guillumette 86-87: (left) Museum of Natural History, Childcraft photo;
Field
*
32-33 James Conahan; Alan Band Associates (right) Rare Coin Co of America, Childcraft photo

34-35 (left) C. Bonongton, Woodfm Camp. Inc. *; 88-89: (left) E R Degginger *; David R. Frazier; (right) Shaw
*
(center) Walter Bonatti, Pictorial Parade "; McCutcheon. Superstock
(right) B Kielczynski, Bruce Coleman Inc. * 90-91: James Conahan. Field Museum of Natural History,
36-37 (left) Paul X. Scott. Sygma *; (right) James Conahan Childcraft photo
*
38-39 Bruce Coleman Inc. 92-93: Childcraft photo, James Conahan
40-41 (left) Alan Band Associates '; (right) Esther Henderson, 94-95: Childcraft photo
*
Rapho Guillumette 96-97. (left) Field Museum of Natural History, Childcraft photo;
42-43: (left) B|orn Bolstad, from Peter Arnold *; (right) Leonard (right) Kaiser Aluminum
& Chemical Corp
Lee Rue III, Bruce Coleman Inc. *
98-99: James Conahan
*
44-45: Giorgio Gualco, Bruce Coleman Inc * 100-101 James Conahan. David Muench
*
46-47: (left) Norman Myers. Bruce Coleman Inc. *; 102-103: (top) E R Degginger \ (bottom) Bill Ratcliffe
*
(center photo) J R Brownlie. Bruce Coleman Inc *; 104-105 David Muench
John Moss, Colorific ";
(right) James Conahan 106-107: (left) Thomas Henley, Tom Stack & Assoc *;
*
48-49 & Press Service
Icelandic Photo (right) Marvin E Newman. Woodfm Camp, Inc '

50-51 Guy Mannering, Bruce Coleman Inc "; James Conahan 108-109 (top) Robert H Glaze. Artstreet ". (bottom) David
' *
52-53 J Alex Langley, DPI Muench
54-55 James Conahan;
(left) (center) J M Brunley. Bruce 110-111: James Conahan
Coleman Inc *, (right) J. Verheyden, Bruce 112-113: Henry Monroe, DPI '; James Conahan
Coleman Inc. * 114-115 James Conahan
'
56-57: (left) Deirdre Wroblewski *; (right) Childcraft photos by 116-117: David R Frazier
Hoppock Associates 118-1 19 Kirsty McLaren
58-59 James Conahan 120-121 James Conahan
*
60-63 Bill Ratchtfe 122-123 Francisco Erize, Bruce Coleman Inc *; James Conahan
64-65 Field Museum of Natural History, Childcraft photos 124-125. (left) Peter Fronk, Van Cleve Photography *; (right) Bill
* *
66-67 (top) H Glaze, Artstreet
Robert '; (bottom) John Gerard Brooks, Bruce Coleman Inc.
'
68-69 (left) James Conahan; (right) James Conahan. 126-127 (left) Aerofilms. Ltd. *, (right) Artstreet
'
Childcraft photo 128-129: (left) Morion Beebe, DPI *; (right) Ed Barans, DPI
70-71: (left) Metropolitan Museum of Art '; (right) Field 130-131 (left) Claude Haycraft, Van Cleve Photography ';
Museum of Natural History, Childcraft photo (right) Ray Atkeson. DPI
'

72-73 Field Museum of Natural History. Childcraft photo 132-133 Oregon State Highway Division "; James Conahan
74-75: (top) Early Japan by Jonathan Norton Leonard and the 134-135. G R. Roberts
*

Editor of Time-Life Books c 1968 Time Inc (Paulus 136-137 APWide World '

*
Leeser) *; (bottom) Field Museum of Natural History, 138-139 James Conahan, Vance Henry, Taurus
Childcraft photo 1 40- 1 4 1 (top) Rodney Allin. Bruce Coleman Inc '; James
'
(left) James Conahan; (right) Department of Energy ', Conahan. (right) Ray Atkeson, DPI
*
Field Museum of Natural History. Childcraft photo 142-143: Barbara Van Cleve
 Illustration acknowledgments 329

144-145 James Conahan 250-251 (upper left) NASA •; (lower left) A. McEwen, U.S.G.S..
•
146-147: NASA Flagstaff Image Processing Facility; (right) Jet Propulsion
'
148-149: James Conahan Laboratory
150-151: (top) Barbara Van Cleve •; (bottom) Grant Heilman
'
252-253 NASA '. James Conahan
152-153 Roman Vishniak '; James Conahan 254-255 James Conahan: NASA '

'
154-163: James Conahan 256-257 (left) James Conahan, (right) Jet Propulsion Laboratory
164-165: (left) James Conahan: (nght) Childcraft pholo 258-259 Herb Hemck
'
166-167 John Stanford. Iowa State University (R D Dockendorff)
'

260-261 Patrick Michaud, Astronomy Magazine

'
168-169: National Oceanic & Atmospheric Administration 262-263 (left) Field Museum of Natural History, Childcraft photo;
' '
170-171: James Conahan: Daniel Farber, Rapho Guillumerte (right) Arizona Office of Tourism
'
172-173 Rod Borland. Bruce Coleman Inc. 264-265: (left) Department of Astronomy. University of Michigan;
" *
174-175 John Deeks (right) Astronomical Society of the Pacific
-
176-177: (left) E R. Degginger ': (right) Tom Stack 266-267 James Conahan
'
178-179: Hubbard Scientific Company {J. A. Day) '
268-269 James Conahan; Minolta Corporation
180-181 (left) James Conahan; (nght) Childcraft photo 270-271 (top) Product Illustration. Inc ;
(bottom) James Conahan
182-183: San Francisco Convention & Visitors Bureau (Sandor 272-273 (top) Product Illustration. Inc ; (bottom) James Conahan
"
Balatoni) 274-275 Herb Hemck
184-185: (left) Childcraft photo: (nght) Grant Heilman
"
276-277 US Naval Observatory
*

*
186-187 E R Degginger
"
278-279 Herb Hemck: U S Naval Observatory
1 88- 1 89 Childcraft photo 280-281 (left) c California Institute of Technology and Carnegie
*
190-191 James Conahan: John Deeks Institution of Washington, from Hale Observatones ':
192-193: John Deeks ': James Conahan US Naval Observatory
(right)
"

194-195: (top) Rural Life Photo Service '; (bottom) National 282-283 World Book photo
'
Center for Atmosphenc Research 284-285 F Yasuhara
196-197: (left) Clyde H. Smith *; (nght) Teisaku Kobayashi 286-287 James Conahan
198-199: Gram Heilman 288-289 (left) NASA •; (right) Childcraft photo by Brent Jones
200-201 Robert H Glaze 290-291 Chicago Aerial Survey ': Childcraft art
202-203: James Conahan 292-293 (left) c Cameramann Intl. Ltd '; (right) Childcraft photo
*
204-205: Onen Ernest. Astronomy Magazine by Brent Jones
206-207 Glenn Van Nimwegen ": James Conahan 294-297 Childcraft art
208-209: US Naval Research Laboratory
'
298-299 Childcraft photos: James Conahan
210-211: Herb Hemck 300-301 (left) Childcraft James Conahan
art; (right)

212-215: James Conahan 302-305 James Conahan

216-217: Tom Stack
"
306-307 Standard Oil Co. (Ind )

218-219: James Conahan 308-309 (left) 5 Peter A. Silva, Picture Group •; (right) E. S.
" '
220-221 Tom Stack Ross
222-223: James Conahan 310-311: (lop) Jed Spiegel, Black Star ', (bottom) Leo Choplin.
'
224-225: James Conahan; George East Black Star
'
226-227: Dan Marrill. Van Cleve Photography 312-313: Childcraft photo by Kyodo News Service
228-229 T. C. Brandt, Van Cleve Photography 314-315: US Geological Survey
'

"
230-231: James Conahan: (top) NASA "; Lick Observatory 316-317: (left) Flip Schulke, Black Star *; (nght) Childcraft photo
232-233: James Conahan by Kyodo News Service
234-235: James Conahan: Steve Larson 318-319: (top) Stephen Krasemann, Science Photo Library *;
*
236-237: NASA \ James Conahan (bottom) Hank Morgan. Science Photo Library
-
238-241 NASA 320-321 (left) NASA •; Douglas Kirkland. Contact Stock •; (nght)
242-243: Herb Hemck; Roberta Polfus NASA •

•
244-245: James Conahan; NASA
246-247: James Conahan; NASA '
Cover: Roberta Polfus
248-249: Technology and Carnegie
E California Institute of
Institution of Washington, from Hale Observatories
';

'
(top) James Conahan; (bottom) NASA
:;::u

calcite (mineral), 67 (picture)

Index in caves, 108
Canopus (star), 272 (with picture)

This index is an alphabetical list of the important topics covered in this canyon, 39-40 (with pictures)

book. It will in both words and pictures.

help you find information given on Mars, 251
To help you understand what an means, there is often a helping
entry Canyon de Chelly (Arizona), 40-
word in parentheses, for example. Achernar (star). If there is 41 (picture)
information in both words and pictures, you will see the words (with Capella (star). 271 (picture)
pictures) after the page number. If there is only a picture, you will see Carina (star group). 272 (with
the word (picture) after the page number. If you do not find what you picture)
want in this index, please go to the General Index in Volume 15, Carlsbad Caverns (New Mexico),
which is a key to all of the books. 109 (picture)
carnotite (mineral), 77
cartographer, work of, 291
Achernar (star), 273 (picture) astrophysicist, work of, 320 Cascade Mountains
Africa Atacama Desert (Chile), 47 (Washington), 24-25 (picture)
land features (picture) Cassiopeia (star group). 271
Nile River, 1 32 (picture) Atlantic Ocean, 13 1 (picture). 272
Sahara, 45 (with picture) atmosphere cassiterite (mineral), 72 (with
Serengeti Plain, 43 (picture) of Earth, 19, 147 (with picture) picture)
air, 148-149 (with pictures) color of sky, 151 (with pictures) cat's-eye (gemstone), 85
see also atmosphere; development of. 35, 153 (with cave
precipitation; water vapor; pictures) formation of, 107 (with pictures)
wind of Jupiter, 252-253 names of

airplane of Mars, 248-251 Carlsbad Caverns (New

contrail of, 185 (with picture) of Venus, 246-247 Mexico), 109 (picture)
in jet stream, 158 see also air Russell Cave (Alabama), 106
air pressure, 154-155 (with Atomic Age, 76 (picture)
pictures) Auriga (star group), 271 (picture). stalactites and stalagmites in,

Alabama 272 1 08 (with pictures)

Russell Cave, 106 (picture) aurora australis and aurora study of, 310 (with pictures)

Alberta (Canada) borealis, 284 (with picture) Cepheus (star group). 271
Mount Rundle, 26-27 (picture) Australia (picture). 272
Algeria Nullarbor Plain, 46-47 (picture) Cer^s (asteroid), 259
Sahara, 45 (with picture) Snowy Mountains, 26 (picture) Chalbi Desert (Kenya), 46
Alpha Centauri (star), 273 autumn, 221-222 (with pictures) (picture)

(picture) azurite (mineral). 64 (picture) Chile

aluminum, 96 (with pictures) Atacama Desert, 47 (picture)
anemometer (weather instrument) China (country)
how to make, 162-165 (with ancient sword of, 73 (picture)
pictures) balloon, weather, 318 (with chlorophyll (plant coloring)
Antarctica, 50-51 (with picture) picture) sunlight used by, 213
Antarctic Circle, 303 (with basalt (rock), formation of, 105 Ciardi, John (poet)

picture) bauxite (mineral), 96 (with Why the Sky Is Blue, 151

Antarctic Ocean, 1 13 picture) cinnabar 78 (picture)
(ore),

Ara (star group), 273 (picture) bay, 1 26 (with picture) cirrus cloud, 178 (with picture)
Arctic Circle, 303 (with picture) beach, formation of, 125 (with cloud, 174-185 (with pictures)
Arctic Ocean, 50-51, 113 pictures) experiment in making, 180-181
Arizona Beaufort Island (Antarctica), 50 (with pictures)
Canyon de Chelly, 40-41 (picture) kinds of, 176-178 (with pictures)
(picture) beryl (mineral), 84 fog, 183 (with picture)
Meteor Crater, 263 (picture) Beta Centauri (star), 273 (picture) from breathing in cold air, 184
asteroid, 243 (with picture), 259 Big Dipper (star group), 271 (with picture)
(with picture) (picture). 272, 299 from jet airplane, 185 (with
astronaut breathing picture)
on moon, 239 (picture), 241 making clouds, 1 84 (with picture) coal. 91 (with picture)
(picture) breeze, 160-161 (with pictures) color
astronomer, work of, 320 (with brimstone, 80 (with picture) in nature
pictures) bronze, 72 (with picture) rainbow, 192-193 (with pictures)
 331

color (continued) day, length of (continued) Earth (continued)

in nature (continued) on Uranus. 256 study of (continued)
sky, 151 (with pictures) on Venus. 247 oceanographers, 317 (with
Colorado Dead Sea (Israel-Jordan) pictures)
Las Animas River. 130 (picture) valley of. 42 (with picture) paleontologists. 308 (with

Columbia River (Washington- degrees of longitude and pictures)

Oregon), 132-133 (picture) latitude. 300 (with pictures) seismologists, 312 (with picture)

waterfall of, 131 (picture) Deimos (moon of Mars), 251 speleologists. 310 (with
comet, 264 (with picture) delta of river, 1 34 (with picture) pictures)
compass, 298 (with picture) Deneb (star), 271 (picture) volcanologists, 315 (with

how to make, 299 (with pictures) desert, 45-46 (with pictures) picture)
condensation. 180-181 (with names of surface of. 18-19 (with picture)
pictures) Atacama Desert (Chile), 47 caves, see cave
see also precipitation (picture) deserts. 45-46 (with pictures),
constellation (star group). 269- Chalbi Desert (Kenya), 46 172
272 (with pictures) (picture) earthquakes, 36-37, 312
constellation (star picture) Nullarbor Plain (Australia), 46 glaciers, 52-55 (with pictures)
charts of, 270-272 (with pictures) (picture) highest place. 31 (with picture)
continents, movement of, 23 Sahara (Africa). 45 (with lakes. 1 38 (with pictures)
(with pictures) picture) lowest place, 42 (with picture)
contrail,185 (with picture) storms in, 172 mountains, see mountain
copper, 71-72 (with pictures) dew, 1 87 (with picture) oceans, see ocean
core of Earth, 17 (with picture) diamond, 66. 83-85 (with picture) plains. 43 (with picture)
Cornwall, Barry (poet) diatom (plant) polar regions, see polar
Sea. The. 112 making oxygen, 153 (with regions
corundum (mineral), 83-84 (with picture) rivers, see river

pictures) dinosaur rock layers, 1 05 (with picture)

cosmic ray, 282 fossils of. 98-100 (with pictures) valleys, 39-42 (with pictures)

crater direction, finding, 298 volcanoes, see volcano

on Earth, 262 (with picture) Draco (star group). 271 (picture). tilt of

on Mercury. 244-245 (pictures) 272 causing seasons, 221-222 (with

on moon. 238. 240 (picture) dust, 56 (with picture) pictures)
crown dust devil, 1 72 (with picture) length of day. 302-303 (with
Holy Roman Empire. 82-83 dust storm, 172 pictures)
(picture) see also atmosphere; map
crust of Earth, 17-19 (with earthquake, 36-37 (with pictures)
pictures) measuring, 312 (with pictures)
see also Earth (surface of) Earth (planet), 6-7 (with picture) eclipse
Crux (star group). 272 (with atmosphere. 1 53 (with picture) lunar, 234 (with pictures)

picture) formation of. 14-15 (with picture) solar, 224 (with pictures)

crystal, 66 (with pictures) oceans, 1 14 electricity

growing, 68-69 (with pictures) inside of, 1 7 (with picture) in lightning, 190 (with picture)

cumulus cloud, 176 (with in solar system, 243 (picture) emerald, 84 (with picture)
picture) orbit of, 10-11 (with picture) energy from sun, 212-215
cyclone, see hurricane causing seasons. 221-222 (with equator, 302 (with pictures)
Cygnus (star group), 271 pictures) seasons on, 222
(picture). 272 photographed from space, 288 erosion
(picture) by glaciers, 53-55 (with pictures)
plates, movement of, 23 (with of mountains, 28 (with picture)
day, length of pictures) valleys formed by, 39-40 (with
on Earth, 9, 217-219. 302-303 spinof, 9 pictures)
(with pictures) causing day and night, 217-219 eruption, volcanic, see volcano
on Jupiter, 253 (with pictures) Escalante Canyon (Utah), 104
on Mars. 251 causing tides, 1 1 9 (with (picture)
on Mercury. 244 pictures) experiments
on moon. 238 study of air, 148-149 (picture)
on Neptune. 257 geologists, 307 (with picture) air pressure. 154-155 (with
on Pluto. 257 meteorologists, 318 (with pictures)
on Saturn, 254 picture) floating ice, 123 (picture)
332

experiments (continued) gold, 86 (with pictures) insect

phases of moon, 232-233 gorge. 39-40 (with pictures) fossil, 103 (picture), 309 (picture)
(pictures) granite (rock), 61, 62 (picture) lo (moon of Jupiter), 252-253
water trom air, 180-181 (with graphite (mineral), 66, 88-89 (with Iran
pictures) pictures) copper sculpture from, 70
see also projects gravity (picture)
effect on atmosphere, 148 iron, 74 (with pictures)
effect on moon, 227 islands, 48 (with pictures)
fall (season), see autumn in formation of solar system, 13- names of

falling star, 259, 260-262 (with 15 (with pictures). 211 Beaufort, 50 (picture)
pictures) of Jupiter, 252-253 Surtsey, 48-49 (pictures)
False Cross (star group), 273 of moon, 240 Isle of Man, 1 26 (picture)
(picture) causing tides, 1 19 Israel
fish of sun, 11, 243 Dead Sea, 42 (with picture)

fossil,103 (picture) Great galaxy, 280 (picture)

flood, 136-137 (with picture) Great Nebula, 277 (picture)
fluorite (mineral), 64 (picture) Grotto Geyser (Wyoming), 142- jade, 85
fog, 183 (with picture) 1 43 (picture) Japan
Follen, Eliza Lee (poet) Grus (star group), 272 (with iron helmet from, 75 (picture)
Oh! Look moon, 230
at the picture) jetstream (wind), 158
Fomalhaut (star), 273 (picture) Guatemala jobs
food chain, 213-215 (with San Pedro volcano, 35 (picture) astronomer, 320 (with pictures)
pictures) astrophysicist, 320
fossil, 98-100 (with picture) geologist, 307 (with picture)
formation of, 1 02 (with pictures) hail, 194 (with pictures) meteorologist,318 (with picture)
study of, 308 (with pictures) halite (mineral), 95 (with picture) oceanographer, 317 (with
frost, 1 98 (with picture) crystals, 66 pictures)
poem about growing crystals, 68-69 (with paleontologist, 308 (with picture)
Jack Frost, 1 98 pictures) seismologist, 312 (with picture)
fuel Halley's comet, 265 (picture) speleologist, 310 (with pictures)
coal, 91 (with picture) hematite (iron ore), 74-75 volcanologist, 315 (with picture)
oil, 92 (with pictures) (picture) Jordan
Hillary, Sir Edmund (mountain Dead Sea, 42 (with picture)
climber), 31 Jupiter (planet), 243 (picture),
galaxy, 280 (with pictures) Hubble space telescope, 320 253 (with pictures)
Milky Way, 278-279 (with (picture)
pictures) hurricane, 161, 169-170 (with
gale (weather), 161 (with pictures) pictures) Kenya (African country)
gamma 282 ray, causing floods, 137 Chalbi Desert, 46 (picture)
Ganymede (moon of Jupiter), on Jupiter. 252-253 (with picture)
252-253 Hydrus (star group), 273 (picture)
gas lake, 138 (with pictures)
in air, 148-149 (with pictures) made by glacier, 55 (with
in nebula, 276 (with pictures) picture)
in solar system, 13-15 (with glaciers, 52-55 (with pictures) Land of the Midnight Sun, 303
pictures) hail and sleet, 194 (with pictures) (with picture)
in sun, 207-208 (with pictures), icicles, 200 (with picture) Las Animas River (Colorado),
21 1 (with pictures) in polar regions, 50-51 (with 1 30 (picture)

nitrogen, 148, 153 picture) latitude, 300 (with picture)

oxygen, 148-149, 153 iceberg, 122-123 (with pictures) lava (melted rock), 32-35 (with
Geiger counter (instrument), 76 Iceland pictures)
gemstones, 83-85 (with pictures) Mount Hekla, 33 (picture) light

geologist, work of, 307 (with Surtsey Island, 48-49 (pictures) speed of, 207-208, 212
picture) 200 (with picture)
icicle, see also sunlight
geyser, 142 (with picture) igneous rock, 61-62 (with lightning, 190 (with picture)
glacier, 52-55 (with pictures) picture) limestone, 61
forming lakes, 138 Indian Ocean, 1 13 caves, 107, 310 (with pictures)
globe (map), 289 (with picture) inlet, 126 formation of, 105
 333

LittleDipper (star group). 271 mine mountain (continued)

(picture).272 salt. 95 Snowy Mountains (Australia), 26
longitude, 300 (with picture) mineral, 65 (with picture) (picture)
lunar eclipse, 234 (with pictures) crystals of, 66 (with pictures) river in, 128-132 (with pictures)

names of see also volcano

azurite, 64 (picture) Mount Everest (Nepal-Tibet), 31
mackerel sky, 178 bauxite. 96 (with picture) (with picture)
magma (melted rock), 32 (with beryl, 84 Mount Hekla (Iceland), 33
pictures) calcite, 67 (picture), 108 (picture)
magnet carnotite, 77 Mount Rundle (Alberta. Canada).
incompass, 298 (with picture) cassiterite, 72 (with picture) 26-27 (picture)
malachite (mineral). 64 (picture) cinnabar, 78 (picture) Musca (star group), 272 (with
mammoth (prehistoric animal), corundum, 83-84 (with pictures) picture)
308 (picture) 64 (picture)
fluonte,
man in the moon, 227 gemstones. 83-85 (with
mantle of earth, 17 (with picture) pictures) navigation
map, 289-297 (with pictures) graphite. 66, 88-89 (with by stars, 268
Earth pictures) nebula, 276 (with pictures)
millions of years ago, 22 halite, 95 (with picture), see Neptune (planet), 242 (picture),

(picture) halite 257 (with picture)

kinds of, 293 (with pictures) hematite, 74-75 (picture) New Mexico
globe, 289 (with picture) iron, 74 (with picture) Carlsbad Caverns, 109 (picture)
treasure, 301 (picture) malachite. 64 (picture) New Zealand
longitude and latitude. 300 (with pitchblende. 77 (with picture) Tongariro River Delta. 135
pictures) pynte. 66 (picture)
marble (rock), 62 (with picture) quartz, 66 (with picture) night and day, see day, length
Mariana Trench (Pacific Ocean), selenite, 64 (picture) of
121 sulfur, 80 (with picture) Nile River (Africa), 132 (picture)
Mars (planet). 243 (picture), 248- uranium, 76-77 (with pictures) nitrogen in atmosphere, 148,
251 (with pictures) wulfenite, 64 (picture) 153
mercury (metal). 79 (with see also metal; rock Norgay, Tenzing (mountain
pictures) moon of Earth, 6-7 (with picture), climber), 31
Mercury (planet). 243 (picture), 227-240 (with pictures) Northern Hemisphere
244-245 (with pictures) causing tides, 1 19 constellations of. 270-272 (with
meridian, 300 (with pictures) eclipse of moon, 234 (with picture)
metal pictures) length of day in, 302-303 (with
aluminum, 96 (with pictures) eclipse of sun, 224 (with pictures)
bronze. 72 (with picture) pictures) seasons in, 222 (with pictures)
copper, 71-72 (with pictures) poem about northern lights, 284 (with
gold.86 (with pictures) Oh! Look at the Moon, 230 picture)
iron.74 (with pictures) moons of other planets, 242-243 North Pole, 50-51. 113. 222 (with
mercury, 79 (with pictures) (with picture) pictures)
silver, 86 (with pictures) Jupiter, 252-253 northern lights, 284 (with picture)

tin,72 (with picture) Mars, 251 (with picture) sun in, 302-303 (with pictures)
uranium, 76-77 (with pictures) Neptune, 257 North Star
metamorphic rock, 61-62 (with Pluto, 257 finding, 299
picture) Saturn. 254-255 nova (exploding star), 274
meteor, 260-262 (with pictures) Uranus, 256 Nullarbor Plain (Australia), 46-47
meteor crater, see crater mountain, 25-35 (with pictures) (picture)
meteorite, 262 (with picture) formation of, 28 (with pictures)
meteoroid, 259. 260-262 (with highest, 31 (with picture)
pictures) in ocean, 120-121 (with picture) oasis in desert, 45 (with picture)
in solar system. 243 names of observatory, 323 (with picture)
moon crater, 238 Cascade Mountains ocean, 112-121 (with pictures)
meteorologist, work of, 318 (with (Washington), 25 (picture) bays. 1 26 (with picture)

picture) Everest (Asia), 31 (with picture) beaches. 125 (with pictures)

Milky Way Galaxy, 278-279 (with Rundle (Alberta, Canada), 26-27 bottom of. 120-121 (with picture)
pictures) (picture) formation of, 153
334

ocean (continued) planet (continued) projects (continued)

icebergs, 122-123 (with pictures) solar system, 242-243 (with compass, 299 (picture)
poem about picture) crystal growing, 68-69 (with
Sea, The, 112 Uranus. 256 (with picture) pictures)
salt water, 1 27 (with picture) Venus, 246-247 (with pictures) rain gauge, 188 (with picture)
study of, 317 (with pictures) see also moon see also experiments
waves, 1 1 6 (with picture) plant pyrite (mineral), 66
oceanographer, work of, 317 food making process of, 213-214
(with pictures) plate (geology), movement of, 23
oil, 92 (with pictures) (with pictures) quartz (mineral), 66 (with picture)
Oneonta Gorge (Oregon), 38 Plough (star group), 271 (picture), quicksilver, 79 (with pictures)
(picture) 272
opal, 84 (with picture) Pluto (planet), 242 (picture), 257
orbit (path in space) (with pictures) radar
of Earth, 10-11 (with picture), poems and rhymes in weather forecasting, 318
221-222 (with pictures) Jack Frost, 1 98 radiation
of other planets, 242 Oh! Look at the Moon, 230 from space, 282
ore, see metal Sea, The. 112 radio telescope, 283 (picture)
Oregon Why the Sky Is Blue, 151 use of, 320
Columbia River, 132-133 poets radio waves, 282
(picture) Ciardi, John, 151 rain
Oneonta Gorge, 38 (picture) Cornwall, Barry, 1 12 cause of, 174
Orion (star group), 268 (with Follen, Eliza Lee, 230 clouds, 176-178
pictures) Setoun, Gabriel, 198 hurricane, 169-170 (with picture)
oxygen in atmosphere, 148-149, Polaris 271 (picture)
(star). in deserts, 45
153 polar regions, 50-51 (with measuring, 188 (with picture)
picture) rainbow, 192-193 (with pictures)
day and night, 302-303 (with rain gauge, 188 (with picture)
pictures) rapids, river,1 30 (with picture)

PacificOcean, 113 glaciers, 53 red planet, see Mars

Mariana Trench, 121 icebergs, 122-123 (with pictures) Rhone Valley (Switzerland), 40
paleontologist, work of, 308 northern and southern lights, 284 (picture)
(with pictures) (with picture) Ring Nebula, 277 (picture)
parallels of latitude, 300 (with pollution ring of Jupiter, 252-253 (with
pictures) mercury, 79 picture)
Pavo (star group), 272 (with pond, 138 rings of Saturn, 254-255 (with
picture) precious stones, 83-85 (with picture)
peat, 91 pictures) river, 128-132 (with pictures)
Perseus (star group), 271 precipitation (water in air) beaches, 125
(picture), 272 dew, 187 (with picture) 1 34 (with picture)
delta,
petroleum, 92 (with pictures) experiment in making, 180-181 dumping salt in ocean, 127
phases of moon, 231-232 (with (with pictures) flood, 136-137 (with picture)
pictures) hail and sleet, 1 94 (with pictures) forming lakes. 138
Phobos (moon of Mars), 251 see also rain; snow forming valleys, 39-40 (with
(with picture) prehistoric animals pictures)
Phoenix (star group), 273 fossils of, 98-100, 102 (with names of
(picture) 308 (with
pictures). pictures) Columbia (Washington-Oregon),
pitchblende (mineral), 77 (with prehistoric people 131 (picture), 132-133
picture) tools used by, 71-72 (with (picture)
plain, 43 (with picture) pictures) Las Animas (Colorado), 130
planet, 6 (with picture) prehistoric plants (picture)
asteroids, 243, 259 (with picture) coal made from, 91 (with picture) 132 (with picture)
Nile (Africa),
Earth, see Earth oil made from, 92 Tonganro (New Zealand), 135
Jupiter, 252-253 (with pictures) pressure, air, 154-155 (with (picture)
Mars, 248-251 (with pictures) pictures) rock, 61-62 (with pictures)
Mercury, 244-245 (with pictures) prime meridian, 300 beach of, 1 25 (with picture)
Neptune, 257 (with picture) projects layers of, 1 05 (with picture)
Pluto, 257 (with pictures) anemometer, 162-165 (with study of, 307 (with picture)
Saturn, 254 (with pictures) pictures) see also limestone; mineral
ruby (gemstone), 84 (with picture) solar system, 242-243 (with stream, mountain, 128-129 (with
Russell Cave (Alabama), 106 picture) pictures)
(picture) asteroids,259 (with picture) sulfur, 80 (with picture)
comets, 264 (with pictures) summer
Sahara (desert in Africa), 44 (with meteoroids, 260-262 (with cause of, 221-222 (with pictures)
picture) pictures) sun, 6-7, 207-208 (with pictures)
salt in seawater, 127 (with see also moon of earth; moons day and night, 217-219 (with

picture) of other planets; planet; star; pictures)

salt, table, see halite sun Earth's orbit, 10-11 (with picture)
sand, 56 (with picture) sonar, 317 (picture) eclipse of moon, 234 (with

beach of, 1 25 (with picture) Southern Cross (star group), 272 pictures)
sand pillar, 172 (with picture) (with picture) eclipse of sun, 224 (with

sandstone, 61. 63 (picture) finding south with, 299 pictures)

formation of, 105 Southern Hemisphere finding direction with, 298
sandstorm, 172 constellations of. 270-272 (with formation of, 1 3 (with pictures),
San Francisco (California) picture) 21 1 (with picture)
earthquake damage, 36 (picture) length of day in, 302-303 (with in polar regions, 51
San Pedro volcano (Guatemala). pictures) seasons caused by, 221-222
35 (picture) seasons in, 222 (with pictures) (with pictures)
sapphire, 83-84 (with picture) southern lights, 284 (with see also solar system
satellite, artificial picture) sunlight
weather, 318 South Pole, 50-51, 113 energy from, 212-215
satellite, natural, see moon glacier, 53 rainbow, 192-193 (with pictures)
Saturn (planet), 242 (picture), southern lights. 284 (with picture) reflected by moon, 228 (with
254-255 (with pictures) sun 302-303 (with pictures)
in, picture)
sea, see ocean space, outer, 204 sunrise and sunset, 217-219
sea level, measuring from, 31 see also universe (with pictures)
seasons space probe, 252-256 supernova (exploding star), 274
cause of, 221-222 (with pictures) speed of light, 207-208, 212 surface of Earth, see Earth
sedimentary rock, 61 63 ,
speleologist, work of, 310 (with (surface of)

(picture) pictures) Surtsey Island (Iceland), 48-49

seismograph (instrument), 312 spider (pictures)
(with picture), 315 web, 186 (picture) Switzerland
seismologist, work of, 312 (with spring (season), 221-222 (with Rhone Valley, 40 (picture)

picture) pictures)
selenite (mineral), 64 (picture) spring (water), 141 (with pictures)
Serengeti Plain (Tanzania), 43 stalactites and stalagmites, 108 Tanzania (Africa)

(picture) (with pictures) Serengeti Plain, 43 (picture)

Setoun, Gabriel (poet) star, 267-280 telescope
Jack Frost, 198 constellations, 268-272 (with radio, 283 (picture), 320
shooting star, 259, 260-262 (with pictures) use of, 320 (with picture)
pictures) finding direction with, 299 temperature
silver (metal). 86 (with pictures) formation of, 21 1 (with picture) highest recorded, 47
sinkhole, 138 galaxies, 278-280 (with pictures) lowest recorded, 51
sky nebula, 276 of sun, 208
color of, 151 (with pictures) nova, 274 thermometer
poem about twinkling, 267 mercury in, 79 (with picture)
Why the Sky Is Blue, 151 see also sun thunder, 190
slate (rock), 62 steel, 74 tide, 1 1 9 (with pictures)
sleet, 194 Steel Age, 74 tiltmeter (instrument), 315
snow Stone Age, 71-72 tin, 72 (with picture)
icicles, 200 (with picture) storm (weather), 161 Titan (moon of Saturn), 254-255
snowflakes, 196 (with pictures) clouds, 176-178 Tongariro River (New Zealand),
Snowy Mountains (Australia). 26 sand and dust. 172 135 (picture)
(picture) thunder and lightning, 190 (with tornado, 1 67 (with picture)
soil picture) treasure map, 301 (picture)
composition 56 (with pictures)
of, tornado, 1 67 (with picture) trench (ocean), 121 (with picture)
made from 35 lava, see also hurricane Triangulum Australe (star group),
solar eclipse, 224 (with pictures) stratus cloud, 1 76 (with picture) 272 (with picture)
336

Tropic of Cancer, 302-303 (with Venus (planet), 243 (picture), waves

pictures) 246-247 (with pictures) ocean, 1 16 (with picture)
Tropic of Capricorn, 302-303 volcano, 32-35 (with pictures) radiation, 282
(with pictures) forming atmosphere, 153 weather
turquoise, 85 forming islands, 48 (with anemometer (instrument), 162-
twister (tornado), 167 (with pictures) 1 65 (with pictures)

picture) forming oceans, 1 14 forecasting, 318 (with picture)

typhoon, see hurricane lakes in, 138 (with picture) see also cloud; precipitation;
names of rain; snow; storm
Mount Hekla, 33 (picture) Whirlpool galaxy, 281 (picture)
San Pedro (Guatemala), 35 whirlwind (tornado), 167 (with
universe, 204 (with picture)
(picture) picture)
nebula, 276 (with pictures)
study of, 315 (with picture) wind, 156-172 (with pictures)
radiation in,282 (with picture) anemometer (instrument), 162-
volcanologist, work of, 315 (with
study of, 320 (with pictures)
picture) 65 (with pictures)
1

see also galaxy; moon; planet; hurricane, 169-170 (with

Voyager 1 and Voyager 2 (space
solar system; star; sun
probes), 252-256 pictures)
uranium (mineral), 76-77 (with strength of. 160-161 (with
pictures)
pictures)
Uranus (planet), 242 (picture),
tornado, 167 (with picture)
Washington (state)
256 (with picture)
Cascade Mountains, 24-25 winter
Ursa Major (star group), 271
221-222 (with pictures)
(picture) cause of,
(picture), 272
Columbia River, 131 (picture), wulfenite (mineral), 64 (picture)
Ursa Minor (star group), 271
132-133 (picture) Wyoming
(picture), 272
water Grotto Geyser, 142 (picture)
Utah
geysers, 142 (with picture)
Escalante Canyon, 104 (picture)
in air, see precipitation; water

vapor
X ray, 282
in caves, 107 (with pictures)
valley, 39 (with pictures) seawater, 1 27 (with picture)

names of underground, 141 (with picture)

Canyon de Chelly (Arizona), 40- waves in ocean, 116 (with year
41 (picture) picture) on Earth, 1
Dead Sea, 42 (with picture) waterfall, 131 (with picture) on Jupiter, 253
Escalante (Utah), 104 (picture) water table, 141 (with picture) on Mars, 251
Oneonta Gorge (Oregon), 38 water vapor on Mercury, 244
(picture) breathing clouds, 184 (with on Neptune. 257
Rhone Valley (Switzerland), 40 picture) on Pluto.257
(picture) experiment with, 180-181 (with on Saturn,254
vapor trail, 1 85 (with picture) pictures) on Uranus, 256
Vega (star), 271 (picture) in clouds, 174 (with picture) on Venus, 247
Veil Nebula, 276 (picture) in dew, 187 (with picture)
Vela (star group), 272 (with in fog, 183 (with picture)
picture) in snowflakes, 196 (with pictures) zircon (gemstone), 85
 r-zxffif

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