能量的来源(The source of Energy)

asummaryofthephysicalandchemicalnatureoflifemustbegin,notontheearth,butinthesun;infact,atthesunsverycenter.itisherethatistobefoundthesourceoftheenergythatthesunconstantlypoursoutintospaceaslightandheat.

thisenergyislibratedatthecenterofthesunasbillionsuponbillionsofnucleiofhydrogenatomscollidewitheachotherandfusetogethertoformnucleiofhelium,andindoingso,releasesomeoftheenergythatisstoredinthenucleiofatoms.theoutputoflightandheatofthesunrequiresthatsome600milliontonsofhydrogenbeconvertedintoheliuminthesuneverysecond.thisthesunhasbeendoingforseveralthousandsofmillionsofyear.

thenuclearenergyisreleasedatthesunscenterashigh-energygammaradiation,aformofelectromagneticradiationlikelightandradiowaves,onlyofverymuchshorterwavelength.thisgammaradiationisabsorbedbyatomsinsidethesuntobereemittedatslightlylongerwavelengths.thisradiation,initsturnisabsorbedandreemitted.

astheenergyfiltersthroughthelayersofthesolarinterior,itpassesthroughthex-raypartofthespectrumeventuallybecominglight.atthisstage,ithasreachedwhatwecallthesolarsurface,andcanescapeintospacewithoutbeingabsorbedfurtherbysolaratoms.averysmallfractionofthesunslightandheatisemittedinsuchdirectionsthatafterpassingunhinderedthroughinterplanetaryspace,ithitstheearth.