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1、ZQ国国PaSSaHe1TheLayersoftheSunConsidertheearth,themoon,andalltheotherplanetsinoursolarsystem.Thinkaboutthemassthatallthoseobjectsmusthavewhentheyarealladdedtogether.Counter-intuitively,addedalltogethertheyaccountforonly0.2%ofthetotalmassofthesolarsystem.Thesunmakesuptheremaining99.8%ofallthemassinthe
2、solarsystem!Thesunisthecenterofthesolarsystemandthelargestobjectinthesolarsystem.OursunisastarthatprovideslightandheatandsupportsalmostalllifeonEarth.Thesunisasphere,butunliketheearthandthemoonzitisnotsolid.Mostatomsinthesunexistasplasmazorafourthstateofmattermadeupofsuperheatedgaswithanelectricalch
3、arge.Oursunconsistsalmostentirelyoftheelementshydrogenandheliumzandbecausethesunisnotsolid,itdoesnothaveadefinedouterboundary.Itdoes,however,haveadefiniteinternalstructure.Thereareseveralidentifiablelayersofthesun:Thecoreistheinnermostorcentrallayerofthesun.Thecoreisplasmazbutmovessimilarlytoagas.It
4、stemperatureisaround27milliondegreesCelsius.Inthecore,nuclearreactionscombinehydrogenatomstoformhelium,releasingvastamountsofenergyintheprocess.Theenergyreleasedthenbeginstomoveoutwardztowardstheouterlayersofthesun.Justoutsidethecoreistheradiativezone,whichhasatemperatureofabout7milliondegreesCelsiu
5、s.Theenergyreleasedinthecoretravelsextremelyslowlythroughtheradiativezone.Particlesoflightcalledphotonscanonlytravelafewmillimetersbeforetheyhitanotherparticleinthesun,areabsorbedandthenreleasedagain.Itcantakeaphotonaslongas50millionyearstotravelallthewaythroughtheradiativezone.Surroundingtheradiati
6、vezoneistheconvectionzone.Here,hotmaterialfromnearthesunscenterrises,coolsatthesurface,andthenplungesbackdownwardtoreceivemoreheatfromtheradiativezone.Thismovementhelpstocreatesolarflaresandsunspots.Thesefirstthreelayersmakeupwhatwewouldactuallycallthesun.Thenextthreelayersmakeupthesunsatmosphere.Of
7、course,therearenosolidlayerstoanypartofthesun,sotheseboundariesarefuzzyandindistinct.Thevisiblesurfaceofthesunisknownasthephotosphere.Thisistheregionofthesunthatemitssunlight.Itsalsooneofthecoolestlayersofthesun-onlyabout6700oC.Lookingataphotographofthesunssurface,youcanseethatithasseveraldifferentc
8、olors:oranges,yellowandredszgivingitagrainyappearance.Wecannotseethiswhenweglancequicklyatthesunasoureyescantfocusthatquicklyandthesunistoobrightforustolookatformorethanabriefmoment.Lookingatthesunforanylengthoftimecancauseblindness,sodonttryit!Sunlightisemittedfromthesunsphotosphere.Afractionofthel
9、ightthattravelsfromthesunreachesEarth.Ittravelsaslightinarangeofwavelengths,includingvisiblelight,ultraviolet,andinfraredradiation.Visiblelightisallthelightwecanseewithoureyes.Wecantseeultravioletorinfraredradiation,buttheireffectscanDD国BIstillbedetected.Forexample,sunburniscausedbyultravioletradiat
10、ionwhenyouspendtoomuchtimeinthesun.Thechromosphereisthezoneabout2,000kilometersthickthatliesdirectlyabovethephotosphere.Thechromosphereisathinregionofthesunsatmospherethatglowsredasitisheatedbyenergyfromthephotosphere.Temperaturesinthechromosphererangefromabout4000oCtoabout10,000oC.Jetsofgasfireupth
11、roughthechromosphereatspeedsupto72,000kilometersperhour;reachingheightsashighas10,000kilometers.Theoutermostlayerofthesunzandtheoutermostpartofitsatmosphere,iscalledthecorona.Itisthesunshaloorcrown.Ithasatemperatureof2to5milliondegreesCelsiusandismuchhotterthanthevisiblesurfaceofthesunzorphotosphere
12、.Thecoronaextendsmillionsofkilometersintospace.Ifyoueverhavethechancetoseeatotalsolareclipse,youwillbeabletoseethesunscorona,shiningoutintospace.Toconclude,inthesunscore,nuclearfusionreactionsgenerateenergybyconvertinghydrogentohelium,andtherestofthesunisheatedbythemovementofthisenergyoutwardfromthe
13、core.Lightenergyfromthesunisemittedfromthephotosphere,andittravelsthroughspace,andsomeofitreachestheearth.ThesunisthesourceofalmostalltheenergyonEarthandsunlightpowersphotosynthesis,aswellaswarmingandilluminatingourEarth.Adaptedfrom:https:en.wikibooks.orq/Wiki/HiqhSChOOlEarthSCienCe/TheSUcSS国IELTSADVANTAGEDailySkillsClinic:LabellingaDiagramPracticeQuestions1-4Labelthediagrambelowwiththenamesofthelayersofthesun.ChooseNOMORETHANTWOWORDSfromthereadingpassageforeachanswer.
