thEEArth
powEr AnD light
CompArED to thE rEst oF thE univErsE, thEEArth is vEry smAll. our plAnEt AnD sEvEn othErs orBit thE sun, whiCh is only onE oF ABout 200 Billion stArs in our gAlAxy. our gAlAxy, thE milky wAy, is pArt oF thE univErsE, whiCh inCluDEs millions oF othEr gAlAxiEs AnD thEir stArs AnD plAnEts.By CompArison, thEEArth is miCrosCopiC、
CompArED to A pErson, on thE othEr hAnD, thEEArth is Enormous. it hAs A DiAmEtEr oF 7,926 milEs ( 12,756 kilomEtErs) At thE EquAtor, AnD it hAs A mAss oF ABout 6 ~ 1024 kilogrAms. thEEArth orBits thE sun At A spEED oF ABout 66,638 milEs pEr hour (29.79 kilomEtErs pEr sEConD).Don’t DwEll on thosE numBErs too long, though; to A lot oF pEoplE, thEEArth is inConCEivABly, minD-Bogglingly Big.AnD it’s just A FrACtion oF thE sizE oF thE sun.
From our pErspECtivE onEArth, thE sun looks vEry smAll. this is BECAusE it’s ABout 93 million milEs AwAy From us. thE sun’s DiAmEtEr At its EquAtor is ABout 100 timEs BiggEr thAnEArth’s, AnD ABout A millionEArths CoulD Fit insiDE thE sun. thE sun is inConCEivABly, minD-Bogglingly BiggEr.
But without thE sun, thEEArth CoulD not Exist. in A sEnsE, thEEArth is A giAnt mAChinE, Full oF moving pArts AnD ComplEx systEms.All thosE systEms nEED powEr, AnD thAt powEr ComEs From thE sun.
thE sun is An Enormous nuClEAr powEr sourCE--through ComplEx rEACtions, it trAnsForms hyDrogEn into hElium, rElEAsing light AnD hEAt.BECAusE oF thEsE rEACtions, EvEry squArE mEtEr oF our plAnEt’s surFACE gEts ABout 342 wAtts oF EnErgy Fi’om thE sun EvEry yEAr. this is ABout 1.7 x 1017 wAtts totAl, or As muCh As 1.7 Billion lArgE powEr plAnts CoulD gEnErAtE. you CAn lEArn ABout how thE sun CrEAtEs EnErgy in how thE sun works.
whEn this EnErgy rEAChEs thEEArth, it proviDEs powEr For A vAriEty oF rEACtions, CyClEs AnD systEms. it DrivEs thE CirCulAtion oF thE AtmosphErE AnD thE oCEAns. it mAkEs FooD For plAnts, whiCh mAny pEoplE AnD AnimAls EAt. liFE onEArth CoulD not Exist without thE sun, AnD thE plAnEt itsElF woulD not hAvE DEvElopED without it.
to A CAsuAl oBsErvEr, thE sun’s most visiBlE ContriButions to liFE ArE light, hEAt AnD wEAthEr. night AnDDAy
somE oF thE sun’s BiggEst impACts on our plAnEt ArE Also its most oBvious.As thEEArth spins on its Axis, pArts oF thE plAnEt ArE in thE sun whilE othErs ArE in thE shADE. in othEr worDs, thE sun AppEArs to risE AnD sEt. thE pArts oF thE worlD thAt ArE in DAylight gEt wArmEr whilE thE pArts thAt ArE DArk grADuAlly losE thE hEAt thEy ABsorBED During thE DAy.
you CAn gEt A sEnsE oF how muCh thE sun AFFECts thEEArth’s tEmpErAturE By stAnDing outsiDE on A pArtly ClouDy DAy. whEn thE sun is BEhinD A ClouD, you FEEl notiCEABly CoolEr thAn whEn it isn’t. thE surFACE oF our plAnEt ABsorBs this hEAt From thE sun AnD Emits it thE sAmE wAy thAt pAvEmEnt ContinuEs to givE oFF hEAt in thE summEr AFtEr thE sun goEs Down. our AtmosphErE DoEs thE sAmE thing--it ABsorBs thE hEAt thAt thE grounD Emits AnD sEnDs somE oF it BACk to thEEArth.
thEEArth’s rElAtionship with thE sun Also CrEAtEs sEAsons. thEEArth’s Axis tips A littlE—ABout 23.5 DEgrEEs. onE hEmisphErE points towArD thE sun As thE othEr points AwAy. thE hEmisphErE thAt points towArD thE sun is wAnnEr AnD gEts morE light—it’s summEr thErE, AnD in thE othEr hEmisphErE it’s wintEr. this EFFECt is lEss DrAmAtiC nEAr thE EquAtor thAn At mE polEs, sinCE thE EquAtor rECEivEs ABout thE sAmE Amount oF sunlight All yEAr. thE polEs, on thE othEr hAnD, rECEivE no sunlight At All During thEir wintEr months, whiCh is pArt oF thE rEAson why thEy’rE FrozEn.
most pEoplE ArE so usED to thE DiFFErEnCEs BEtwEEn night AnD DAy (or summEr AnD wintEr) thAt thEy tAkE thEm For grAntED、But thCsE ChAngEs in light AnD tEmpErAturE hAvE An Enormous impACt on othEr systEms on our plAnEt. onE is thE CirCulAtion oF Air through our AtmosphErE. For ExAmplE:
thE sun shinEs