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THE EARTH AND BEYOND(天地之间).doc

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THE EARTH AND BEYOND(天地之间).doc

THEEARTHANDBEYONDThesolarsystemTheuniversecontainsover100billiongalaxies.Agalaxyisagroupofbillionsofstars.OurowngalaxyiscalledtheMilkyWay,anditcontainsabout100billionstars,includingourSun.TheSunisatthecentreofthesolarsystem.ThesolarsystemcontainsdifferenttypesofobjectsincludingastartheSunplanets,whichgoaroundtheSunsatellites,whichgoaroundplanetssmallerobjectssuchasasteroidsandcometsHeliocentricmodelPeopleusedtothinkthattheEarthwasatthecentreoftheuniverse,witheverythinggoingaroundit.Wenowknowthatthisisnotcorrect.Theideathatfitsscientificobservationsandallowsustopredictthemovementoftheplanetsiscalledtheheliocentricmodel.ThisjustmeansthattheSunisatthecentreofthesolarsystem,andtheEarthandotherplanetsgoaroundit.WesaythattheplanetsareinorbitaroundtheSun.TheplanetsinorderfromtheSunMercurytoPlutoAlthoughscientistshavediscoveredsomeextraobjectsorbitingtheSunthatmaybeplanets,normallyweassumethattherearenineplanetsinthesolarsystem.Inorder,workingawayfromtheSun,theseareMercury,Venus,Earth,Mars,Jupiter,Saturn,Uranus,NeptuneandPluto.Ifyoucantrememberthecorrectorder,trythissentence,ormakeoneupofyourownMyVeryEasyMethodJustSpeedsUpNamingPlanetsGravitationalforcesAllobjectshaveaforcethatattractsthemtowardseachother.Thisiscalledgravity.Gravityonlybecomesnoticeablewhenthereisareallymassiveobjectlikeamoon,planetorstar.YoucanfindoutmoreaboutgravityintheRevisionBiteForcesandmotion/Massandgravity.GravityandthesolarsystemGravitationalforcesbetweentheSunandplanetskeeptheplanetsmovinginorbitaroundtheSun.Withouttheseforces,theplanetswouldflyoffintodeepspace.Theirorbitsareslightlysquashedcirclescalledellipses.Diagramsoftenshowtheorbitsasverysquashed,butthisisjusttogetasenseofperspectiveandtofitthediagramsontothepage.AstheplanetsgetfurtherfromtheSunthespeedthattheplanetmovesdecreasesthetimetocompleteanorbitincreasesOrbitgraphForexample,Mercurytakesjust88Earthdaystocompleteanorbit,whilePlutotakes248Earthyearstocompleteanorbit.TheplanetsfurthestfromtheSunarealsothecoldestbecausetheyreceivetheleastheatenergyfromtheSun.DaysandnightsTheplanetsspinastheyorbittheSun.Adayisthetimetakenforaplanettomakeonecompleteturnonitsaxis.Differentplanetstakedifferentamountsoftimetodothis.AnEarthdayis24hoursittakestheEarth24hourstomakeonecompleteturnonitsaxis.ItisdaytimeforuswhenourpartoftheplanetisfacingtheSun,anditisnighttimeforuswhenourpartoftheplanetisfacingawayfromtheSun.OnewaytorememberwhichwaytheEarthturnsistorememberWEspin,whichmeanstheEarthspinsfromwesttoeast.DaysDuringtheday,theSunappearstomovethroughthesky.RememberthatthishappensbecausetheEarthisspinningonitsaxis.IfwelooksouthandplottheSunintheskyduringtheday,wefindthatitappearstomovelikethisSunintheskyPTheSunappearstomovefromeasttowest.Itrisesintheeastandsetsinthewest.Atmiddaywefacesouthtoseeit.NightsDuringthenight,wecannotseetheSun.ButtheEarthisstillspinningonitsaxis.Thismeansthatthestarsappeartomovefromeasttowestinthesky,justastheSundoesintheday.StartrailsmadebyleavingthecamerashutteropenduringthenightYearsandseasonsYearsAplanetsyearisthetimetakenforittomakeonecompleteorbitaroundtheSun.TheEarthtakes365EarthdaystoorbittheSun.RememberthatdifferentplanetstakedifferentlengthsoftimetodothisthefurtherfromtheSun,thesloweraplanettravelsandthelongeritsorbittakes.SeasonsTheEarthsaxisistiltedslightlycomparedtothewayitorbitstheSun.BecauseofthistiltingoftheEarthsaxis,wegetthedifferentseasonswinter,spring,summerandautumn.WhenitissummerintheUK,theNorthernHemisphereistiltedtowardstheSun.WhenitiswinterintheUK,theNorthernHemisphereistiltedawayfromtheSun.SeasonsintheNorthernHemisphereThingstonoteWhenitissummerintheNorthernHemisphere,itiswinterintheSouthernHemisphere.TheSunappearstobehigherintheskyinthesummerthanitdoesinthewinter.SeasonsintheNorthernHemisphereTheMoonTheMoonisthenaturalsatelliteoftheEarth.ItorbitstheEarthbutnoonebuiltitorlauncheditintospace.GravitationalforcesbetweentheMoonandtheEarthkeeptheMooninorbit.TheMoonisnotaluminousobject,soitdoesnotmakeitsownlight.Instead,itreflectslightfromtheSunwhich,liketheotherstars,isaluminousobject.Asatellitehastotravelatthecorrectspeedtostayinorbitataparticulardistancefromaplanet.IttakestheMoon28daystomakeacompleteorbitoftheEarth.Asitorbits,weseedifferentamountsoftheMoon,soweseedifferentphasesoftheMoon.RememberthatwecanonlyseethepartoftheMoonthatreflectstheSunslight.HowmuchofthatwecanseedependsuponthepositionoftheMooninitsorbit.ThephasesoftheMoon,seenfromtheEarthAcommonmistakeistothinkthatthephasesoftheMoonhappenbecausetheEarthgetsintheway,andcastsashadow.However,ifthisdoeshappen,wegetaneclipseoftheMoonThephasesoftheMoon,seenfromtheEarth.ArtificialsatellitesandspaceprobesArtificialsatellitesArtificialsatellitesarebuiltbypeopleandlaunchedintoorbitaroundtheEarth.Theyareveryusefultous.ThesearesomeofthethingsthatartificialsatellitesareusedforCommunications,includingbroadcastingtelevisionprogrammesandrelayingtelephonecallsGlobalPositioningSystemGPSandGalileosatellitesfornavigationCollectinginformationtohelpwithweatherforecastsScientificsurveysoftheEarthssurfaceMapmakingSpyingSomesatellitesareusedtocollectinformationabouttheplanetsandstars.TheHubbleSpaceTelescopecanseefurtherintospacethantelescopesbasedontheground.Itsviewisnotblockedbycloudsanditdoesnthavetowaitfornighttime.However,itisdifficultandexpensivetolaunchandmaintain.Ifanythinggoeswrong,onlyastronautscanfixit.SpaceprobesSpaceprobesdonotorbittheEarth.Instead,theytraveltootherplanetstocollectscientificinformation.PeoplehavebeentotheMooninthelastcentury,butitwouldtaketoolongtosendpeopletootherplanets.Somespaceprobesgointoorbitaroundotherplanets,somelandonthem,andsomeevenjourneyoutofthesolarsystem.

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