Illustrations: RebeccaW.Keller,PhD,JanetMoneymaker,MarjieBasslerEditor: MarjieBassler

Copyright©2013GravitasPublications,Inc.

Allrightsreserved.Nopartofthispublicationmaybereproduced,storedinaretrievalsystem,ortransmitted,inanyformorbyanymeans,electronic,mechanical,photocopying,recording,orotherwise,withoutpriorwrittenpermissionfromthepublisher.Nopartofthisbookmaybeusedorreproducedinanymannerwhatsoeverwithoutwrittenpermission.

Focus On Middle School Astronomy Student Textbook (softcover)

ISBN#978-1-936114-47-4

PublishedbyGravitasPublications,Inc.www.gravitaspublications.com

PrintedinUnitedStates

iiiCONTENTS

ContentsCHAPTER 1: WHAT IS ASTRONOMY? 1 1.1 Introduction 2 1.2 EarlyAstronomers 2 1.3 ModernAstronomers 4 1.4 ChangingViewsoftheCosmos 5 1.5 Summary 7

CHAPTER 2: ASTRONOMERS’ TOOLBOX 8 2.1 Introduction 9 2.2 Telescopes 10 2.3 SpaceTools 12 2.4 Summary 13

CHAPTER 3: EARTH IN SPACE 14 3.1 Introduction 15 3.2 TheEarthinSpace 15 3.3 TheEarthandtheMoon 18 3.4TheEarthandtheSun 20 3.5 Eclipses 21 3.6 Summary 23

CHAPTER 4: THE MOON AND THE SUN 24 4.1 Introduction 25 4.2 TheMoon 25 4.3 TheSun 28 4.4 ChemistryandPhysicsofStars 29 4.5 Summary 31

CHAPTER 5: PLANETS 32 5.1 Introduction 33 5.2TypesofPlanets 33 5.3 Earth-likePlanets 34 5.4 Jupiter-likePlanets 36 5.5 WhatHappenedtoPluto? 39 5.6 Summary 41

CHAPTER 6: OUR SOLAR SYSTEM 42 6.1 Introduction 43 6.2 PlanetaryPosition 43 6.3 PlanetaryOrbits 44 6.4 Asteroids,Meteorites,andComets 46 6.5 HabitableEarth 48 6.6 Summary 49

iv CONTENTS

CHAPTER 7: OTHER SOLAR SYSTEMS 50 7.1 Introduction 51 7.2 Closeststars 51 7.3 Constellations 53 7.4 BrightestandLargestStars 54 7.5 PlanetsNearOtherStars 55 7.6 TheCircumstellarHabitableZone 56 7.7 Summary 57

CHAPTER 8: OUR GALAXY 58 8.1 Introduction 59 8.2 TheMilkyWay 60 8.3 ShapeandSize 61 8.4 GalacticHabitableZone 64 8.5 Summary 65

CHAPTER 9: OTHER GALAXIES 66 9.1 Introduction 67 9.2 SpiralGalaxies 68 9.3 BarredSpiralGalaxies 69 9.4 EllipticalGalaxies 71 9.5 IrregularGalaxies 71 9.6 Summary 72

CHAPTER 10: THE UNIVERSE 73 10.1 Introduction 74 10.2 RedGiantsandWhiteDwarfs 74 10.3 NovaeandSupernovae 75 10.4 BlackHolesandNebulae 77 10.5 AUniverseWeCanDiscover 81 10.6 Summary 81

Glossary - Index 82

2FOCUSONMIDDLESCHOOLASTRONOMY

1.1IntroductionAstronomyisconsideredbymanytobetheoldestscience.Sincelongbeforetheinventionofthetelescope,humanbeingshavebeenlookingatthestars.Thewordastronomy(ǝ-strä’-nǝ-mē)comesfromtheGreekwordasterwhichmeans“star”andtheGreekwordnomaswhichmeans“toassign,distribute,orarrange.”Thewordastronomyliterallymeans“toassignorarrangethestars.”Astronomersarescientistswhoassignnamestoallthecelestial(sǝ-les’-chǝl)bodiesinspace,includingstars,andstudyhowtheyexistandmoveinspace.

1.2EarlyAstronomersTheearliestrecordedhistoryrevealsaninterestinthestars.Cavedrawingsshowprimitivehumansrecordingobservationsfromtheskies,andlatertheBabylonians(ba-bǝ-lō’-nyǝnz)recordeddetailedplanetarypositions,eclipses,andotherastronomicalobservations.EgyptianandGreekobserversexpandedontheinformationcollectedbytheBabylonians.ThealignmentofthepyramidswiththeNorthStarsuggeststhattheEgyptiansacquiredsophisticatedabilitiestoobservethesky.TheAncientGreekswerethefirstastronomerstoaddmathematicstoastronomy.

Manyearlycivilizationsusedthestarsandthemovementsofcelestialbodiesastoolstomeasuretime.TheSumerians(sü-mer’-ē-ǝnz)ofBabyloniausedthephasesoftheMoontocreatethefirstlunarcalendar,and

CHAPTER1:WHATISASTRONOMY?3

theEgyptians,Greeks,andRomanscopiedandrevisedthiscalendar.TodayourcalendarisderiveddirectlyfromtheSumeriancalendarandisconnectedtothemonthlyandyearlyorbitsoftheMoonandEarth.Ontheothersideoftheocean,theIncanandMayancivilizationscreatedsophisticatedcalendarsbyobservingtheplanetarycycles.TheMayancalendariscircularandhasaspectsthatrelatethemovementoftheSun,Moonandplanets.

Earlyastronomersnamedindividualstarsaswellasgroupsofstarsthatformconstellations(kän-stǝ-lā’-shǝnz).Aconstellationisanygroupofstarsthatfit

togethertoformapatterninthenightsky.SomeofthemajorconstellationsthatcomefromGreekmythologyarefamiliartomanypeople.Orion(ǝ-rī’-ǝn)theHunterisaconstellationofstarsthatcanbeseenfromthenorthernhemispherefromDecemberthroughMarch.Orionhasa“belt”ofthreebrightstarsinastraightrow.Oncethe“belt”islocated,itiseasytofindthe“club”and“shield”bylookingforneighboringstars.

Orion

4FOCUSONMIDDLESCHOOLASTRONOMY

TheconstellationnamesderivedfromGreekmythologyhavechangedverylittlesince1000BC(BCE).Therearecurrently88constellationsthatarerecognizedbytheInternationalAstronomicalUnion(IAU),andoverhalfofthosewereobservedbytheancientGreeks!

1.3ModernAstronomersToday,astronomerscanseemanymorestarsthantheirancientpredecessorscould.Modernastronomerscanalsoseedetailsabouttheplanetsandstarsthatwerenotvisibleinancienttimes.

InChapter2wewilllookcloselyatthetoolsamodernastronomerusestolookatcelestialbodies.Telescopes,radios,andcamerasarejustsomeofthetoolsastronomersusewhenstudyingtheplanetsandstars.Modernastronomersalsousechemistryandphysicstounderstandastronomicaldata.Understandinghowplanetsmoverequiresknowingthephysicsbehindgravity,inertia,andmass.Understandinghowstarsgiveoffheatandlightenergyrequiresknowingthechemistrybehindnuclearreactions.AndunderstandinghowtheSunaffectsourweatherrequiresknowledgeofmagneticandelectricfields.Modernastronomersnotonlyhavesophisticatedtoolstoexploretheuniverse,theyalsohavecenturiesofcomplicatedmathematics,chemistry,andphysicstohelpthemunderstandhowtheuniverseworks.

CHAPTER1:WHATISASTRONOMY?5

1.4ChangingViewsoftheCosmosThepracticeofastronomychangeddramaticallyaftertheinventionofthetelescope,ascientifictoolthatuseslensestomagnifydistantobjects.Inthe1600’sGalileo(ga-lǝ-lā’-ō),anItalianscientistconsideredtobethefirstmodernastronomer,usedthetelescopetolookattheplanets.GalileowasalsoabletoseethemoonsofJupiterandtherotationoftheSun.Basedonhisobservations,Galileoconfirmedaradicalnewviewofthecosmos(käz’-mōs).Thecosmos,orsolarsystem,includesourSunandtheplanetsaroundit.

InancienttimesmostpeoplebelievedthattheEarthwasthecenteroftheuniverse.TheseancientsbelievedthattheplanetsandtheSunmovedinacircularorbit,orpath,aroundtheEarth.Thisviewoftheworldiscalledgeocentric(jē-ō-sen’-trik).GeocomesfromtheGreekwordgewhichmeans“earth”or“land”andcentriccomesfromtheGreekwordkentronwhichmeans“point”or“center.”AgeocentricviewisonethatconsiderstheEarthasthetruecenteroftheuniverse.

Geocentric Cosmos

6FOCUSONMIDDLESCHOOLASTRONOMY

Itisnothardtounderstandwhythisviewwasheld.SteppingoutsideatanygiventimeofthedayandobservingthemotionoftheSun,itlooksliketheSunrotatesaroundtheEarth.AgeocentricviewoftheuniversewasfirstproposedbyAristotle(a’-rǝ-stä-tǝl)(384-322BC[BCE])andwasthedominantbeliefheldbymostpeopleformanycenturies.

However,noteveryoneagreedwithAristotle.AristarchusofSamos(a-rǝ-stär’-kǝsofsā’-mäs),wholivedfrom310-230BC(BCE),wasanexpertGreekastronomerandmathematicianwhodidnotbelievethattheSunandplanetsrevolvedaroundtheEarth.Hewasthefirsttoproposeaheliocentric(hē-lē-ō-sen’-trik)cosmos.ThewordheliocentriccomesfromtheGreekwordhelioswhichmeans“sun.”AheliocentriccosmosisaviewoftheuniversewiththeSunasthecentralpointandtheEarthandplanetsorbitingtheSun.

Heliocentric Cosmos

CHAPTER1:WHATISASTRONOMY?7

AlthoughtodayweknowthatAristarchuswasright,hisproposalwasrejectedbyhiscolleaguesbecauseitseemedtocontradicteverydayobservation.IftheEarthwasnotstable(centralandnotmoving),howdideverythingnotbolteddownkeepfromflyingofftheEarthasitrotatedaroundtheSun?ThephysicsofAristotlewasthescientificconsensusviewduringAristarchus’lifetimeandthatmeantthataheliocentriccosmoswouldhaveviolatedthelawsofphysics!Itwasalmost2000yearsbeforetheideaofaheliocentriccosmoswasreintroducedbyNicolausCopernicus(kō-pǝr’-ni-kǝs)(1473-1543)andconfirmedbythescientificobservationsofGalileo.

Today,astronomersdonotbelieveinageocentriccosmosandknowthatourEarthorbitstheSunandthatweliveinaheliocentricsolarsystem.Moderntechnologies,adeeperunderstandingofphysics,andawillingnesstochallengeprevailingscientifictheorieswereneededbeforethegeocentricviewcouldbereplacedbythemoreaccurateheliocentricviewofthecosmos.

1.5Summary

• Astronomyisthefieldofsciencethatstudiescelestialbodiesandhowtheyexistandmoveinspace.

• Earlyastronomerswereabletomapthemovementsoftheplanetsandstarsandusedcelestialmotionstocreatecalendars.

• Modernastronomersusechemistryandphysicstogetherwithmoderntechnologiestostudytheuniverse.

• Ancientpeoplesoncebelievedinageocentriccosmos,orEarth-centereduniverse.TodayweknowthatweliveinaheliocentricsolarsystemwiththeSunatthecenter.