g5 lsr 1g 5.17 earth in space

8/12/2019 G5 LSR 1G 5.17 Earth in Space

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Scott Foresman Science 5.17

Genre Comprehension Skill Text Features Science Content

Nonction Make Inferences • Captions• Charts• Diagrams• Glossary

The Solar System

ISBN-13:ISBN-10:

978-0-328-34246-40-328-34246-7

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9 0 0 0 0

by Donna Latham

Space and Technology



Illustration: 1, 4, 6, 7, 21 Bob KayganichPhotographs: Every effort has been made to secure permission and provide appropriate credit forphotographic material. The publisher deeply regrets any omission and pledges to correct errors called to itsattention in subsequent editions. Unless otherwise acknowledged, all photographs are the property of ScottForesman, a division of Pearson Education. Photo locators denoted as follows: Top (T), Cente r (C), Bottom(B), Left (L), Right (R) Background (Bkgd)Opener: (B) NASA Image Exchange, (TC) Getty Images; 2 NASA; 3 ©Lowell Georgia/Corbis; 4 ©DaveRobertson/Masterfile Corporation; 8 (CL, CC, CR) Getty Images, (CL) JPL/NASA, (CC) Corbis, (CR)©Comstock, Inc.; 9 (CC) JPL/NASA, (CL) ©NASA/Roger Ressmeyer/Corbis; 10 (CC) Corbis, (Bkgd)©Handout/Reuters/Corbis; 12 ©Phil Degginger/Color-Pic, Inc.; 13 ©GSFC/NASA; 14 ©NASA/DKImages; 15 (BR) ©JPL/TSADO/Tom Stack & Associates, Inc., (CC) ©TSADO/NASA/Tom Stack &

Associates, Inc.; 16 ©Charles & Josette Lenars/Corbis; 18 (TR, BR) NASA Image Exchange; 19 GettyImages; 20 Getty Images; 21 ©Eckhard Slawik/Photo Researchers, Inc.; 22 (CL, B) Jeff Newbery; 23 (TR)NASA, (CL) Getty Images, (TC) ©Eckhard Slawik/Photo Researchers, Inc.

ISBN 13: 978-0-328-34246-4; ISBN 10: 0-328-34246-7

Copyright © Pearson Education, Inc.

All Rights Reserved. Printed in the United States of America. This publication isprotected by Copyright and permission should be obtained from the publisher priorto any prohibited reproduction, storage in a retrieval system, or transmission in anyform by any means, electronic, mechanical, photocopying, recording, or likewise. Forinformation regarding permissions, write to: Permissions Department, Scott Foresman,1900 East Lake Avenue, Glenview, Illinois 60025.

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Vocabulary asteroid

axis

comet

Moon phase

revolution

rotation

satellite

solar system

space probe

Earth in Spaceby Donna Latham



In what ways doesEarth move?Earth’s Orbit

The solar system is made up of the Sun, its eight planets,many moons, asteroids, and comets. Earth is a small, blue,ball-shaped planet in the solar system. It has one moon. Eachof the planets follows its own path around the Sun. This path,called an orbit, is not exactly round. It is elliptical, or shapedlike a flattened circle.

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A revolution is one orbit. It takes Earth just a little morethan 365 days to make its revolution around the Sun. Does365 sound like a familiar number to you? It should! It’s a year . The Moon’s revolution around Earth doesn’t take nearly thatlong. It takes about 28 days, or about a month .

What keeps the planets in their orbits around the Sun? It’sgravity. Gravity is the force that keeps you on the Earth. Thepull of gravity is very strong. Gravity also keeps the Moonorbiting around the Earth.



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Day and NightPlanets spin. This causes any part of the planet to face the

Sun for a while. Then that part turns away from the Sun. Whenour part of Earth faces the Sun, we have day. When it turnsaway from the Sun, we havenight. The spinning of Earth

causes the changes of dayand night.

Look at the picture of thespinning top. You can seethat it tilts, or leans as itmoves. A top spins around animaginary line called an axis. Earth spins, or rotates, on anaxis too.

This diagram shows Earth’stilt. It also shows its spin. TheNorth Pole is at the top of theaxis. The South Pole is at thebottom.

Earth’s axis is an imaginary line.It is not really there. But if youpicture it in your mind, you cansee how Earth spins.

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A rotation is one spin of an objecton its axis. Earth completes a rotationin 24 hours. That’s one day. Earth’stilt causes some parts of the planetto receive more daylight than others.Depending on where people live, thelength of day and night changes allyear. The change is greater in some

places than others. On one day inspring and one day in fall, day

and night are the same length.

Earth’s ComfortableTemperature

Because of the speed ofEarth’s rotation, day followsnight quickly. So, the Earthdoes not get too hot or toocold. Earth also has an

atmosphere, or layer of gases,to help control temperature. It

reflects some of the Sun’s raysto keep us cool, but also traps

some to keep us warm. Some

planets and our Moon have littleor no atmosphere. Their temperaturechanges are too extreme for livingthings to survive.



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The Pattern of SeasonsThe pattern of changes which we call the seasons is caused

by Earth’s tilt. Earth always tilts the same way during its orbit.So at different times of year, different parts of Earth tilt towardthe Sun. Those parts receive more daylight hours. They are alsowarmer, because sunlight hits them at a more direct angle.

Daylight lasts longer in the summer. It is shorter in the winter.Look at the diagram below. It shows Earth’s revolution

around the Sun. Do you see how the Sun is not exactly in themiddle of Earth’s orbit? The distance between Earth and the Sunchanges throughout the year. But this distance does not affectour seasons.

January

147,500,000 km

152,600,000 km

Earth

Sun

July

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Around June 21,Summer:The NorthPole tilts toward theSun. The Sun’s mostdirect rays fall on theNorthern Hemisphere.So it has the mostdaylight hours andbecomes warmer.

Around September 21,Fall:The hours of daylightand night are equal.

Around December 21, Winter:The NorthPole has its greatestslant away fromthe Sun. Daylight isshorter than on anyother day of the year.

Around March 21, Spring:The hours of daylight and nightare equal.

Earth’s SeasonsThis diagram shows the seasons for the Northern Hemisphere, where theUnited States is located. The seasons change as the Earth orbits the Sun.But the tilt of Earth’s axis never changes.

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Our solar system is made up of the Sun and its eight planets.This diagram shows the position of the planets in the solarsystem. The diagram is not to scale, because if it were, it wouldnot fit on the page. The planets are too far apart. Planets closeto the Sun move quickly and have small orbits. Planets far fromthe Sun move slowly and have large orbits. Their revolutionstake many Earth years.

What are the partsof the solar system?

Mercury

Venus

Earth

asteroid belt

Mars

Jupiter

Saturn

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Because the planetsare so far away fromone another, and spaceis so huge, the unitsof measure we use onEarth don’t work verywell. They are muchtoo small. Scientists useAUs, or astronomicalunits, instead of milesor kilometers. OneAU is the averagedistance between Earthand the Sun.

Uranus Neptune

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Planet Diameter(Compared to Earth)

Mercury 0.4

Venus 0.9

Mars 0.5

Jupiter 11.0

Saturn 10.0

Uranus 4.0

Neptune 4.0

Planet Diameters



Visiting the PlanetsSpace probes have been used to explore the planets for years.

Space probes are spacecraft that can gather data withoutany people aboard to run them. But they do carry specialinstruments. With them, space probes find out about planetsurfaces and what they are made of.

Mariner 10, a space probe,has given us pictures ofMercury’s surface.

In 2004, the Mars roversSpirit and Opportunity werelanded on Mars. They sentcolor pictures back to Earth.

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Mercury Scientists think Mercury’s core is mostly

made of iron. Mercury has almost noatmosphere. Mercury’s surface temperaturecan go from –170°C to 430°C .

VenusVenus is the closest planet to Earth. Venusis just as hot during the night as it is duringthe day. That’s because the Sun’s heat getstrapped in the planet’s thick clouds. Venus’satmosphere is made up of poisonous gases.

MarsMars has a very thin atmosphere. It looks

red because of the reddish-brown iron in itssoil. Mars has giant volcanoes. It also has icecaps at its poles.

The Gas GiantsPast Mars are four “gas giant” planets.

They are Jupiter, Saturn, Uranus, andNeptune. These huge planets are giganticballs of gas. These planets all have many

moons and rings.

PlutoPluto is a dwarf planet. Scientists think

it is made of ice and rock. Pluto’s moon,Charon, is about half the size of the planetitself! Some scientists call Pluto and Charona “double planet.”



What are cometsand asteroids?Comets

Comets are icy, dusty masses orbiting the Sun. Theremay also be rocky matter inside them. Much smaller thanplanets, comets come from beyond Pluto. Their paths arevery stretched out.

Each year, a few comets enter our solar system and circlethe Sun. But only the very largest ones can be seen withouta telescope.

Nucleus A comet’s nucleus has an unevenshape. Scientists call it a “dirtysnowball.” Made of dust andice, the nucleus grows blackand solid over time. The nucleusis very small, sometimes only afew kilometers across.

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A comet is made up of a solid core called a nucleus and acloud of dust and gas called a coma. Look at the diagram tolearn more about each part of a comet.

Coma Around the nucleus is a giant cloud of dust andgases. The coma can be even larger than theplanet Jupiter. The fine dust reflects sunlightbrightly. The gases take in energy and glow.It’s the coma that gives a comet its fuzzy look.The coma and tail form only when the cometgets close to the Sun. There, sunlight melts partof the nucleus.

Two TailsComets have two tails. They stream out in adirection away from the Sun. The tails may beup to 80 million kilometers long! The ion tail ismade of tiny, magnetic particles of gas. It is thinand blue in color and sticks straight out from thecomet. The dust tail is wide and yellow. It is madeof dust that is released by the melting nucleus.

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AsteroidsAn asteroid is a rocky mass that revolves around the Sun

and is much smaller than a planet. Asteroids can be severalhundred kilometers wide, but some are as tiny as pebbles.Many asteroids have odd, uneven shapes. And some even havesmaller asteroids that orbit them. Jupiter’s gravity holds most

asteroids in a belt beyond Mars, but occasionally one will hitEarth. Take a look at these images of asteroids.

By a noseHere’s an asteroid with an odd shape!Some people think it looks like a flyingnose. The largest asteroids, though, aremore ball-shaped, like the planets.

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Asteroid ErosLook at the surface of Eros. Can youspot the craters, boulders, and rocklayers? More than 33 kilometers longand 13 kilometers thick, Eros is thefirst asteroid to be landed on

by a spacecraft.

Asteroid IdaIda is about 58 kilometers longand 23 kilometers wide. It is inthe asteroid belt between Marsand Jupiter.

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Meteors, Meteoroids, and MeteoritesSmall asteroids are called meteoroids. They are usually the

size of a grain of sand but can be as big as a boulder. Whenmeteoroids hit Earth’s atmosphere, they become meteors. Theyheat up and make a glowing streak across the night sky. Youmay have seen this happen but called it a shooting star. Very

bright meteors are called fireballs. When Earth passes throughthe orbit of a comet, we see many meteors at once. This is calleda meteor shower.

Arizona’s Meteor Crater

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Although most meteors burn up before they crash intoEarth, some do not. Then, pieces of them may fall to Earth.A meteorite is a piece of rock or metal that lands on Earth.Most are very small, but sometimes a large one lands, causinggreat damage.

This crater was caused by a small meteorite.It is about two hundred meters deep andtwelve hundred meters across.

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What is knownabout the Moon?Traveling with Earth

At about 384,000 kilometers(238,000 miles) away, the Moonis Earth’s closest neighbor. Youmight not think that sounds veryclose. But compared to everythingelse in our solar system, the Moonis quite close.

The Moon is the only place,other than Earth, where peoplehave stood. It is also Earth’s onlynatural satellite. A satellite is an object in orbit aroundanother object.

Looking at the MoonAs the Moon orbits Earth, we

can see only one side. Called thenear side, this half of the Moonfaces Earth at all times. That’sbecause the Moon spins and orbitsat about the same speed. It takesthe Moon about 27 days to orbit theEarth. In the same amount of time,it rotates once.

The Moon’s Surface

The Moon is covered withmountains, craters, andsmooth plains. Craters werecaused by rocks or cometscrashing into the Moon.The Moon has no air orwater, but it does havesome ice. At one timelava flowed on theMoon, creatinglarge areas ofsmooth rock.

Visiting the MoonOn July 20, 1969, Neil Armstrong

became the first person to stepon the Moon. From 1969 to 1972,twelve people walked on the Moon.

This is the near side ofthe Moon. That’s thehalf that faces Earth,and the side we see.

A satellite took thisphoto of the farside of the Moon.

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Neil Armstrong



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Phases of the MoonHave you noticed that the

Moon appears to changeshape at different timesof the month? Thesedifferent shapes are

called Moon phases.Although the Moonoften looks very brightin the sky, it doesn’treally produce any light.“Moonlight” is reallysunlight reflecting off theMoon’s surface. Only one sideof the Moon is lit by the Sun.

At different times of the month,different amounts of the litside face Earth. This is why theMoon seems to change shape.

When we see the Moon fromEarth, we see its lit side. As the

Moon orbits Earth, differentamounts of this side can be seen.

Over a month, the Moon appears indifferent shapes. We call them phases.

View from Earth

New MoonYou can hardly see a new Moon!It passes between the Earth andthe Sun. The side in shadow facesEarth. The sunlit side faces away.

Crescent MoonFor a few days after the newMoon, you can see a crescentMoon. It is a little slice of theMoon’s sunlit side.

Full MoonYou can see the full Moonabout a week after the firstquarter. Earth is between theMoon and the Sun.

First Quarter MoonThe first quarter Moon is seenabout a week after the new Moon.Half of the Moon’s sunlit sidefaces Earth.

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High and Low TidesIf you’ve ever spent a day at an ocean beach, you know that

the ocean has high and low tides. The water level rises and thengoes back down. There are two high tides and two low tideseach day.

The Moon’s gravity causes the tides. It makes the ocean

bulge out toward the Moon. Tides are high in the areas thatbulge out, and low in the areas that don’t. As the Moon movesaround Earth, the bulge moves with it, causing the high tides totravel around the world.

The Bay of Fundy isfamous for its tides. Theyare the highest in the

world, reaching 15 meters(50 feet). At low tide,boats end up sittingin the mud!

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The Sun’s gravity affects the tides too. But it is a muchsmaller effect than the Moon’s. During a full Moon or newMoon, the Sun and Moon both pull on the Earth. At this timethe highest tides take place. At the first quarter or third quarterMoon, things are different! The Sun pulls on Earth at one angle.The Moon pulls at another. This causes the lowest tides.

In this short journey around the solar system, you’ve learnedmany things. You have learned that it is made up of the Sunand its planets —including Earth. You have also learned thatthe Moon, meteors, comets, and asteroids are also part of thesolar system.

You have learned that Earth’s orbit causes many things tohappen. For example, day becomes night. Seasons change.Tides rise and fall. And the phases of the Moon occur eachmonth. Our neighbors in the solar system may be far away,but they have a big effect on our world!

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Glossary asteroid a rocky mass orbiting the Sun that can be

several hundred kilometers wide

axis the imaginary line around which Earthrotates, or spins

comet a frozen mass of ice and dust that orbitsthe Sun

Moon phase the changes in shape the Moon goes throughin a month as seen from Earth

revolution one full orbit of an object around anotherobject

rotation one whole spin of an object on its axis.

satellite an object that orbits another

solar system the Sun and all the bodies that orbit it

space probe a spacecraft that gathers data without a crew

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What Did You Learn?1. What is one cycle that is caused by Earth’s movement in

space?

2. What caused the Moon’s craters?

3. Most of the asteroids in our solar system are located in a belt

between Mars and Jupiter. Why is this?4. The motion of objects in space

causes cycles to take place. One cycle, for example, is the year that passes as Earth makes its way around the Sun. On your own paper, write about another cycle that takes place.Include examples and details from the book to support youranswer.

5. Make Inferences Look back at the diagram onpage 7. Study the facts about each season in the NorthernHemisphere. When would each season begin in the SouthernHemisphere? Why do you think this is so?

g5 lsr 1g 5.17 earth in space

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