California Leveled Science Readers (Grade 5) Content leveled readers teach science concepts, vocabulary, and reading skills – at each student’s reading level – and allow students to read and explore the wonders of nonfiction. Leveled science readers deliver science content to help address the individual needs of all students. They reinforce reading skills and strategies while promoting science understanding. Each grade 5 science reader is a richly illustrated, selfcontained little book with 10 to 14 double pages. BELOW 5.1 Building Blocks of Matter (Physical Sciences) 5.2 Changes in Matter (Physical Sciences) 5.3 Basic Structures of Organisms (Life Sciences) 5.4 MISSING 5.5 Water on Earth (Earth Sciences) 5.6 Weather (Earth Sciences) 5.7 The Solar System (Earth Sciences) ON 5.1 Understanding Matter (Physical Sciences) 5.2 How Matter Changes (Physical Sciences) 5.3 The Building Blocks of Organisms (Life Sciences) 5.4 Systems of the Human Body (Life Sciences) 5.5 Earths Hydrosphere (Earth Sciences) 5.6 How Weather Works (Earth Sciences) 5.7 Earths Solar System (Earth Sciences) ADVANCED 5.1 Atoms (Physical Sciences) 5.2 Acids and Bases at Work (Physical Sciences) 5.3 MISSING 5.4 MISSING 5.5 MISSING 5.6 Hurricanes (Earth Sciences) 5.7 The Red Planet (Earth Sciences)
Trang 1Standards Preview
Genre Comprehension Skill Text Features Science Content
Nonfi ction Make Inferences • Captions
• Diagrams
• Tables
• Glossary
Solar System
Scott Foresman Science 5.7
Standard Set 5 Earth Sciences
5 The solar system consists of planets
and other bodies that orbit the Sun
in predictable paths As a basis for
understanding this concept:
5.a Students know the Sun, an average
star, is the central and largest body
in the solar system and is composed
primarily of hydrogen and helium.
5.b Students know the solar system
includes the planet Earth, the Moon, the Sun, eight other planets and their satellites, and smaller objects, such as asteroids and comets.
5.c Students know the path of a
planet around the Sun is due to the gravitational attraction between the Sun and the planet.
ISBN 0-328-23471-0
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by Martin E Lee
Earth Sciences
Trang 2asteroid
comet
ellipse
planet
satellite
solar system
star
Picture Credits
Every effort has been made to secure permission and provide appropriate credit for photographic material
The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions.
Unless otherwise acknowledged, all photographs are the copyright © of Dorling Kindersley, a division of Pearson.
10 ©USGS/Photo Researchers, Inc.; 11 JPL/NASA; 12 Getty Images; 16 NASA; 17 JPL/NASA; 19 ©Mark Garlick/Photo
Researchers, Inc.
ISBN: 0-328-23471-0
Copyright © Pearson Education, Inc All Rights Reserved Printed in the United States of America
This publication is protected by Copyright, and permission should be obtained from the publisher prior to any
prohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic,
mechanical, photocopying, recording, or likewise For information regarding permission(s), write to
Permissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025.
1 2 3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06
by Martin E Lee
Trang 3What is the Sun?
The Star of Our Solar System
A star is a huge ball of very hot gas that gives off
energy Our Sun is a star It is the center of the solar system
The solar system is the Sun and its planets It also
includes many moons, asteroids, and comets
The Sun is the largest object in our solar system It has
almost 99 percent of all the mass in our solar system The
Sun also has about one million times the volume of Earth
The Sun’s size is average for a star Stars called giants
can be 8 to 100 times larger in diameter than the Sun
Supergiants can be more than 500 times larger than the
Sun Other smaller stars are only around the size of Earth
The Sun gives off lots of energy The temperature in
the Sun’s center is very high The hydrogen particles move
quickly because of this When these particles hit each other,
they can combine into helium The fusion of hydrogen into
helium makes most of the Sun’s energy
The Sun is the central and largest body in our solar system.
3
The Explosive Sun
The Sun is like a ball of hot gases The Sun has no hard
surfaces, but it does have layers The photosphere is the part
of the Sun that gives off the light energy we can see The
layer above that is called the chromosphere The corona is
the outermost layer of the Sun
If you looked at the Sun through scientifi c instruments, you would see a lot of activity Galileo saw dark spots moving along the face of the Sun We now call these dark
spots sunspots They look dark because they are cooler than
the rest of the photosphere
The number of sunspots does not stay the same The number changes in cycles of about 11 years Sometimes there are many sunspots, at other times there are few
Sunspots may be the size
of Earth or larger.
Trang 4Solar Eruptions
Hot gases may leap out of the
chromosphere They can shoot far into the
corona These glowing ribbons of gas are
called prominences Prominences may
appear and then disappear over a few
days or months
Other explosive things happen
in the chromosphere Parts of the
chromosphere sometimes erupt like
a volcano This is called a solar fl are
A solar fl are looks like a bright spot
in the chromosphere It may last
for minutes or hours A solar fl are
sends out energy into space that
can affect electronics on Earth The
energy can disturb radio signals
and damage electrical systems
Prominences rise with great speed and power Some may get as high as one million kilometers.
Solar fl ares give off more light than other parts of the Sun They also give off more X-rays and other kinds of energy.
5
Trang 5Why do planets
revolve around
the Sun?
The Solar System
Our solar system includes the Sun, the planets, their
moons, and other objects Every object in the solar system
moves around the Sun Their path of movement is called an
orbit The planets’ orbits are shaped like ellipses An ellipse
is a shape like an oval
Remember that our Sun is a star A planet is a large,
round object that moves around a star Planets are cooler
and smaller than stars are Some planets seem to shine, but
they don’t give off their own light A planet shines because
it refl ects the light given off from its star
Venus
Jupiter
Earth
Asteroid belt
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Gravity keeps planets in their orbits Gravity is a force
of attraction between objects The Sun and the planets are attracted to each other by gravity The force of gravity between the Sun and a planet is strong enough to move the mass of the planet But it is not strong enough to move the Sun Planets do not move in straight lines Gravity makes them move in an ellipse around the Sun
The picture below shows the eight known planets of the solar system The four planets nearest to the Sun are called the inner planets The four planets farthest from the Sun are the outer planets Asteroids and comets also revolve around the Sun
Neptune
Uranus Saturn
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Trang 6Gravity and the Moon
The Moon is a satellite of Earth A satellite is an object
that orbits another object in space Most planets in the solar
system have at least one moon Mercury and Venus do not
Our Moon moves in an elliptical orbit around Earth
The force of gravity keeps the Moon in its orbit The Moon’s
mass is much less than that of Earth So gravity between
the Moon and Earth keeps the Moon orbiting Earth
Why doesn’t gravity make the Moon crash into Earth?
The reason is that the Moon is always moving forward
At the same time, the gravity of Earth is always pulling
inward This balance keeps the Moon in a steady orbit
Orbiting the Sun
The Moon orbits Earth while both the Moon and Earth
orbit the Sun This is the same with other planets and their
moons too Gravity between a planet and its moons holds
its moons in orbit And gravity keeps planet-moon systems
in orbit around the Sun
Gravity keeps the Moon in
orbit around Earth.
8
Free Falling
Astronauts in space look weightless But they are really falling in space This effect is called free fall
Gravity on Earth pulls objects toward Earth’s center
Gravity makes a thrown ball follow a curved path The ball moves forward, but it also curves as gravity pulls it down
A ball thrown hard enough would go all the way around Earth This is what happens when a spaceship orbits Earth
The spaceship falls all the way around Earth in an orbit It
is moving forward and downward at the same time
Suppose you are going down a hill in a roller coaster
It feels like you could fl oat out of your seat This is because you and the roller coaster are falling at the same rate The same thing happens in a spaceship orbiting Earth The ship and the astronauts fall together in their orbit Gravity pulls
on them both, but the astronauts can’t feel the effect The astronauts feel weightless inside the spaceship
Astronauts are weightless because they are in free fall.
9
Trang 7What are the inner
planets?
Mercury
Mercury is the planet nearest to the Sun It is a bit
bigger than the Moon Mercury has thousands of low spots
called craters on its surface They were made long ago when
meteorites crashed into Mercury A meteorite is a rock from
space that has hit the surface of a planet or a moon
Scientists sent a space probe called Mariner 10 to
Mercury in 1973 It arrived at Mercury in 1974 A space
probe is a vehicle that studies objects in space using
cameras and other tools
Mercury’s average
surface temperature
is 117°C (243°F).
11
Too Hot and Too Cold
Mercury is blazing hot during the day This is because
it is so near the Sun Its daytime temperatures are over
fi ve times higher than anywhere on Earth But Mercury has almost no atmosphere Without atmosphere, the heat escapes This makes Mercury very cold at night
Venus
Venus is the second planet from the Sun It is about the same size as Earth Venus is very hot and dry, like Mercury
But Venus has an atmosphere of thick clouds These clouds are burning hot and poisonous! There are strong
winds and lightning The clouds refl ect the Sun’s light very well This makes Venus one of the brightest objects you can see in the night sky on Earth
Trang 8Earth is the third planet from the Sun It is the solar
system’s largest rocky planet It is the only planet with
liquid water on its surface
Earth’s atmosphere is about 150 kilometers thick This
thick layer of gas makes life possible on Earth It contains
nitrogen, oxygen, carbon dioxide, water vapor, and other
gases Earth’s plants and animals need these gases The
atmosphere fi lters out some of the Sun’s harmful rays So
far, scientists think Earth is the only planet in the solar
system that can support life
The Moon
Moons are satellites of planets Moons revolve around
planets in the same way that planets revolve around the
Sun Both happen because of gravity And gravity between
a planet and its moons keeps the moons in their orbits
Earth has one large moon It is about one-fourth the size
of Earth The Moon has almost no atmosphere It has many
craters from when meteorites crashed into its surface
Earth’s average surface temperature
is 15°C (59°F).
12
Mars
Mars is the fourth planet from the Sun Its soil has a reddish-brown material in it called iron oxide It makes up rust Mars has two moons Both of them have many craters
Mars has an atmosphere But the atmosphere doesn’t have enough oxygen for plants or animals to live Winds
on Mars cause dust storms that can cover the whole planet!
Mars has ice caps at its poles These ice caps grow in the winter and shrink in the summer Mars has many volcanoes It also has a canyon that is almost ten times longer than Arizona’s Grand Canyon
The Viking I probe landed on Mars in 1976 The
Sojourner robot explored part of Mars in 1997 In 2004,
two robot rovers landed there They were named Spirit and
Opportunity They gathered data and sent it back to Earth
Scientists hope that the data will tell them more about the rocks and soil there They also want to fi nd out if
Mars has or once had water
This is one of the Mars rovers that landed in 2004.
13
Trang 9An asteroid is a rocky object up to several hundred
kilometers wide that revolves around the Sun Sometimes
asteroids are called minor planets Most asteroids are found
in the asteroid belt This area is between Mars and Jupiter
Most asteroids take three to six Earth years to orbit the Sun
Asteroids have uneven shapes Some have smaller asteroids
that orbit them The smallest asteroids are like pebbles
Asteroids have hit Earth You can still see some of the
craters that formed But don’t worry; it happens very rarely
Jupiter’s gravity keeps most asteroids within the space
beyond Mars
Asteroid Eros In 2001,
Eros became the fi rst
asteroid to be landed upon
by a spacecraft Eros is 33
kilometers long and 13
kilometers thick.
Nucleus The nucleus of
a comet may be just a few kilometers wide.
14
Comets
A comet is a frozen mass of different kinds of ice and
dust A comet orbits around the Sun Comets are much smaller than planets Many of them come from parts of the solar system past Pluto They travel through the solar system in very elliptical paths Every year, several comets may enter our solar system and orbit the Sun But you are unlikely to see them You need a telescope to see all but the largest comets
Coma A giant cloud of dust and gases surrounds the nucleus This is called the coma.
Two Tails A comet’s two tails may be up to 80 million kilometers long!
15
Trang 10What do we know
about the outer
planets and beyond?
Jupiter
Jupiter is the fi fth planet from the Sun It is the largest
planet in our solar system It is a gas giant A gas giant is a
very large planet made up mostly of gases Hydrogen and
helium make up most of Jupiter’s atmosphere In 1610,
Galileo used his telescope to see Jupiter’s four largest moons
The diameter of Jupiter
is 142,984 kilometers
(88,846 miles).
17
Saturn
The sixth planet from the Sun is also a gas giant
Saturn’s atmosphere is mostly hydrogen and helium Saturn
is very large but not as dense as the other planets
Saturn is orbited by bright rings The Voyager space
probe found that the rings are made of bits of ice, dust, and rock The bits range in size from tiny grains to large boulders
Uranus
Uranus was discovered in 1781 by William Herschel
It is the seventh planet from the Sun Uranus is the most distant planet you can see without a telescope Uranus is a gas giant Its atmosphere is made up of hydrogen, helium, and methane Uranus is cold enough to make methane condense into a liquid Drops of liquid methane cover Uranus in a cloud They give it a fuzzy blue-green color
Like other gas giants, Uranus has rings and many moons The rings were fi rst seen by a space probe in 1977
Uranus rotates on its side Scientists think that something large may have hit Uranus when the solar system was forming This hit may have
knocked the planet onto its side
Besides rings, Saturn has
at least thirty-four moons.
Trang 11Neptune is the eighth planet from the Sun It is the
smallest of the gas giants You need a telescope to see
Neptune Neptune has a long orbit because it is very far
from the Sun It takes over one hundred Earth years for
Neptune to travel around the Sun
Neptune’s atmosphere is like that of Uranus Methane
in its atmosphere gives it a bluish color Neptune also has
bands of clouds and storms like Jupiter has Neptune had
one huge storm named the Great Dark Spot The Voyager 2
probe saw it in 1989 Five years later, the storm was gone
Neptune was discovered in 1846 Its largest moon,
Triton, was seen just days later Triton may be the coldest
body in the solar system It has a surface temperature of
about -235°C Neptune has at least thirteen moons
Neptune, like Uranus, has rings.
Neptune‘s ring
system
18
Pluto
In 1930, Clyde Tombaugh found a small, rocky object
in space Sometimes it orbits beyond Neptune This object is called Pluto
Pluto is about the same size as Earth’s moon It has a moon called Charon that is just a little smaller than Pluto Pluto has at least two other moons They are called Nix and Hydra
In 2006, scientists decided to call Pluto a dwarf planet
A dwarf planet is a small, round or ball-shaped object that revolves around the Sun
Other Dwarf Planets
In 2005, scientists found a dwarf planet that is a little larger than Pluto The dwarf planet is at least three times farther from the Sun than Pluto It has at least one moon This dwarf planet is called Eris
There is also a dwarf planet called Ceres in the
asteroid belt
Charon is very close to Pluto.
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