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_ Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. L 1 _ 8 8 9 4 0 edn setas h oa ytm The System Solar Reading Essentials The Sun System intheSolar Objects What isthesolar system? System The oftheSolar Structure SystemThe Solar in thesolarsystemtomovearound,ororbit,Sun. Sun’s gravitationalforce causestheplanetsandotherobjects day.as light.Thislightshinesonalloftheplanetsevery The a huge amountofenergy. TheSunemitssomeofthisenergy 99 percent ofthemassentiresolarsystem. mostly ofhydrogengas.TheSun’s massmakesupabout system. Itsdiameterisabout1.4millionkm.TheSunmade Venus, Mars,Jupiter, andSaturn. hadseenonlyfiveplanets—Mercury,Before then,observers ofseveralplanetsandmanyotherspaceobjects. discovery away thananyobjectsinoursolarsystem. Stars arenotpartofthesolarsystem.Theymuchfarther system, butmostarestars.Itishardtotellthedifference. that youcanseeinthenightskyareplanetssolar make upthesolarsystem.Afewoftinyspeckslight 7 this lesson,reread thestatements to seeifyou have changedyour mind. if you agree withthestatement oraDifyou disagree. After you’ve read whether you agree ordisagree withthem.Place anAintheBefore column What doyou think? . i n eoeSaeetAfter Statement Before d d Inside theSun,aprocesscallednuclearfusionproduces The Sunisastarandthelargestobjectinsolar The inventionofthetelescopein1600sledto The Sunandthegroupofobjectsthatmovearoundit

1 2. 1. Gravitational force keepsplanetsinorbit around theSun. usingastronomicalspace units. objects Astronomers measure distances between Readthetwo statements below anddecide this lesson. have reading learnedafter third column, write whatyou you wantto know. the In second column, write what the solarsystem. the In of aboutthestructure know first column, write whatyou into three columns. the In K-W-L • • • Key Concepts S CIENCE around acommoncenter usually hasfiveorsixpoints Common Use that emitenergy nuclear fusionreactionsoccur space madeofgasesinwhich Science Use star planet’s orbit? What istheshapeofa unit andwhy isitused? What isanastronomical planets? different from theouter How are theinnerplanets 3TUDY#OACH Fold asheetof paper U SE

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CHAPTER 21 . C an objectin ashapethat LESSON 1 OMMON U SE

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0 1 / 9 1 / Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. 22/19/10 1:57:33 PM Sun Mercury . Unlike orbit the asteroids Neptune Mars The inner planets are the Earth Venus Uranus . Comets come from the outer parts is made of gas, dust, and ice and moves around the around and moves dust, and ice is made of gas, A dwarf planet is a spherical object that orbits Inner planets Millions of small, rocky objectsMillions called of small, comet A The figure below shows the eight planets in the the eight planets below shows The figure Planets, dwarf planets, asteroids, and comets orbit the orbit comets and asteroids, planets, dwarf Planets, Sun. These objects do not emit light. Instead, they reflect Instead, they reflect emit light. objects do not Sun. These light. the Sun’s solar system. An object is a planet only if it orbits the Sun if it orbits the is a planet only An object solar system. also have spherical shape. The object must and has a nearly of all other larger than the total mass a mass that is much nearby. orbits objects in Comets Dwarf Planets Asteroids Inner Planets and Outer Planets Objects That Orbit the Sun Orbit That Objects Planets Sun—Jupiter, Saturn, Uranus (YOOR uh nus), and Neptune. Saturn, Uranus (YOOR uh nus), Sun—Jupiter, The outer planets are made of ice and gases. four planets closest to the Sun—Mercury, Venus, Earth, and Venus, four planets closest to the Sun—Mercury, of solid, rocky materials. Mars. The inner planets are made planets farthest from the The outer planets are the four Sun in the asteroid belt between the orbits of Mars and Jupiter Sun in the asteroid planets, asteroids usually are not spherical. Sun in an oval-shaped orbit Sun in an oval-shaped orbit the Sun. 1 trillion comets of the solar system. Possibly, the Sun and is not a moon of another planet. Unlike a planet, a dwarf planet does not have more mass than all the objects in nearby orbits. The figure on the next page locates the dwarf planets Ceres (SIHR eez), Eris (IHR is), Pluto, and Makemake (MAH kay MAH kay). Dwarf planets are made of rock and ice and are much smaller than Earth. Jupiter Saturn On the 2

how the inner how

d d n i . Location 7 0 4 9 8 8 Key Concept Check Concept Key _

1 Object L Visual Check Visual _ Solar System The Reading Essentials E R Outer planets _ 4 planets differ from the outer the outer from planets differ planets. 364

2. Describe 1. Interpret 1. Interpret summarize information about information summarize the types objects of that the solar system. make up Make a tri-fold book to Make a tri-fold diagram, circle the inner circle diagram, planet that orbits the Sun Earth.closest to 0 0 _ 1 0 0 _ 4 9 1 CC194_001_004_RE_L1_889407.indd 2 CC194_001_004_RE_L1_889407.indd 3 1 9 4 _ 0 0 1 _ 0 0 4 _ R E

_ Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. L 1 _ 8 8 9 4 0 edn setas h oa ytm The System Solar Reading Essentials OrbitsandSpeeds Planetary Revolution andRotation The MotionofthePlanets The Astronomical Unit 12 timeslongerthanEarthtorevolvearoundtheSun. have longerperiodsofrevolution.Forexample,Jupitertakes moves. ThisalsomeansthatplanetsfartherfromtheSun as itorbits.TheclosertheplanetistoSun,faster moves alongitsellipticalorbit.Aplanet’s speedalsochanges Sun isatonefocus,andtheotherfocusemptyspace. focus points,orfoci,controltheshapeofellipse.The special points,eachcalledafocus,areinsidetheellipse.The of oneday. rotation is its they orbittheSun. of revolutionisoneyear. Theobjectsalsospin,orrotate,as travel once around theSunisits orbit, orrevolve,aroundtheSun. path aroundtheSun. the Sun. Thisforce keepseachplanetmovingalongacurved is theaverage distance from Ear system. Theyuseastronomicalunits. measure thegreatdistancesbetweenobjectsinsolar 0.39 AU,orabout58millionkm. example, theaveragedistanceofMercury fromtheSunis 7 planets . i n Inner d Asteroid d Astronomers needaunitlargerthanthekilometerto A planet’s distancefromtheSunchangesasplanet A planet’s orbitisanellipse—astretched-outcircle. Two Objects inthesolarsystemmovetwoways.Theobjects The Sun’s gravitationalforce pullseachplanettoward

belt 3 Jupiter

period ofrotation. Mars The timeittakes tocomplete foranobject one th to theSun—

Ceres period ofrevolution. Earthhasaperiodofrotation The timeittakes to anobject An about 150

astronomical unit Makemake Pluto Earth’s period million km Neptune . For

(AU) (AU) Saturn Uranus Ceres Kuiper belt explain why itisused. an astronomical unitisand 4 Identify 4. 3. Specify 5. Describe a planet’sorbit. Sun? from the planet isfarthest Visual Check Key Concept Check Key Concept Check Which dwarf Which dwarf Define what the shapeof Eris 365 22/19/10 1:57:40PM / 1 9 / 1 0

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END OF LESSON

d. the time it takes an object to travel an object travel the time it takes to the time it takes an object to complete an object complete the time it takes to ED onnect C once around the Sun around once one rotation Log on to ConnectED.mcgraw-hill.com ConnectED.mcgraw-hill.com on to Log find this to textbook your and access resources. lesson’s

period of revolution: revolution: period of period of rotation: c. Sun

b. the average distance from Earth from distance to the average 4

d d n i . 7 0 one of millions of small, rocky objects orbit the rocky that of small, one of millions 4 9 a mixture of gas, dust, and ice that moves around the the around moves that and ice dust, a mixture of gas, 8 8 _ 1 L Sun in an oval-shaped orbit Sun in an oval-shaped Sun in the asteroid belt between the orbits of Mars and Jupiter the orbits of belt between Sun in the asteroid the Sun—about 150 million km the Sun—about 150 million _ Solar System The Reading Essentials E Based on your K-W-L chart, summarize the new facts you learned from this lesson. chart, summarize the new facts you learned Based on your K-W-L Fill in the blanks below to identify the inner planets in the order of their distance from Fill in the blanks below to identify the Sun. explains the difference between an asteroid and a comet. between an asteroid and explains the difference Review the terms and their definitions in the Mini Glossary. Write a sentence that Write Mini Glossary. and their definitions in the Review the terms agree with the statement or a D if you disagree. disagree. or a D if you the statement with agree mind? change your Did you Reread the statements at the beginning of the at the beginning the statements Reread with an A if you column in the After lesson. Fill R What do you think

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Content Vocabulary LESSON 1 The Structure of the Solar System Directions: On each line, write the term from the word bank that correctly replaces the underlined words in each sentence. Use each term only once. NOTE: You may need to change a term to its plural form.

asteroid astronomical unit comet orbit period of revolution period of rotation star

1. Many objects, including planets, travel around the Sun.

2. Orbiting objects made of gas, dust, and ice come from the outer parts of the solar system.

3. The Sun is a(n) structure in space made of gases in which nuclear fusion reactions occur.

4. In 365 days, Earth completes a(n) full journey around the Sun.

5. In 24 hours Earth completes a(n) full turn, also called a complete spin.

6. Millions of small, rocky objects orbit the Sun between the orbits of Mars and Jupiter.

7. A(n) distance equal of about 150 million km is the average distance from Earth to the Sun. Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. The McGraw-Hill of a division © Glencoe/McGraw-Hill, Copyright

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Lesson Outline LESSON 1 The Structure of the Solar System

A. What is the solar system? 1. The in the solar system orbit the Sun. 2. The Sun and the objects that orbit it make up the . B. Objects in the Solar System 1. The largest object in the solar system is the . a. The Sun is a star made up mostly of gas. b. produces enormous amounts of energy in the Sun. c. Objects orbit the Sun because it applies forces on them. 2. Objects that orbit the Sun include planets, dwarf planets, asteroids, and . These objects the Sun’s light. 3. A planet has a nearly shape. a. The mass of a planet is much than the mass of nearby objects. b. There are planets in the solar system. Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. c. The four planets closest to the Sun are called the planets. d. Inner planets are made mainly from materials. e. The four planets farthest from the Sun are called the planets. f. Outer planets are made mostly of ice and . g. Because the outer planets are much larger than the inner planets, they are sometimes called . 4. A(n) is a spherical object that orbits the Sun, is not the moon of another planet, and has less mass than any of the eight planets. 5. Millions of small, rocky objects called orbit the Sun in a belt between Mars and Jupiter. 6. A(n) orbits the Sun in an oval-shaped orbit and is made of dust, gas, and ice.

10 The Solar System

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Lesson Outline continued

7. The is used to measure long distances in the solar system. 8. One astronomical unit (AU) is the average distance from Earth to the . C. The Motion of the Planets 1. One way an object in the solar system moves is by orbiting, or , around another object. 2. The amount of time it takes an object to revolve once around the Sun is its . 3. Objects in the solar system also spin, or . 4. The time it takes an object to rotate once is its . 5. The shape of a planet’s orbit is a(n) , which is a stretched-out circle. a. The Sun is at one of the of the ellipse, so the distance between a planet and the Sun changes as the planet moves. b. A planet moves when it is closer to the Sun than when it is farther away. Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc. The McGraw-Hill of a division © Glencoe/McGraw-Hill, Copyright

The Solar System 11

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