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Thesunisanordinarystar,oneofabout100billioninourgalaxy,theMilkyWay.
Thesunhasextremelyimportantinfluencesonourplanet:Itdrivesweather,
oceancurrents,seasons,andclimate,andmakesplantlifepossiblethrough
photosynthesis.Withoutthesun’sheatandlight,everythingthatmakeslife
possibleonEarthwouldnotexist.
About4.5billionyearsago,thesunbegantotakeshapefromamolecularcloud
thatwasmainlycomposedofhydrogenandhelium.Anearbysupernovaemitteda
shockwave,whichcameincontactwiththemolecularcloudandenergizedit.The
molecularcloudbegantocompress,andsomeregionsofgascollapsedunder
theirowngravitationalpull.Asoneoftheseregionscollapsed,italsobeganto
rotateandheatupfromincreasingpressure.Muchofthehydrogenandhelium
remainedinthecenterofthishot,rotatingmass.Eventually,thegasesheatedup
enoughtobeginnuclearfusion,andbecamethesuninoursolarsystem.
Otherpartsofthemolecularcloudcooledintoadiscaroundthebrand-newsun
andbecameplanets,asteroids,comets,andotherbodiesinoursolarsystem.
Thesunisabout150millionkilometers(93millionmiles)fromEarth.Thisdistance,
calledanastronomicalunit(AU),isastandardmeasureofdistancefor
astronomersandastrophysicists.
AnAUcanbemeasuredatlightspeed,orthetimeittakesforaphotonoflightto
travelfromthesuntoEarth.Ittakeslightonthesunabout8minutesand19
secondstoreachEarth.
Theradiusofthesun,orthedistancefromtheverycentertotheouterlimits,is
about700,000kilometers(432,000miles).Thatdistanceisabout109timesthe
sizeofEarth’sradius.ThesunnotonlyhasamuchlargerradiusthantheEarth—
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itisalsomuchmoremassive.Thesun’smassismorethan333,000timesthatof
theEarth,andcontainsabout99.8percentofallofthemassintheentiresolar
system!
Composition
Thesunismadeupofablazingcombinationofgases.Thesegasesareactuallyin
theformofplasma.Plasmaisastateofmattersimilartogas,butwithmostofthe
particlesionized.Thismeanstheparticleshaveanincreasedorreducednumber
ofelectrons.
Aboutthreequartersofthesunishydrogen,whichisconstantlyfusingtogether
andcreatingheliumbyaprocesscallednuclearfusion.Heliummakesupalmost
theentireremainingquarter.Averysmallpercentage(1.69percent)ofthesun’s
massismadeupofothergasesandmetals:iron,nickel,oxygen,silicon,sulfur,
magnesium,carbon,neon,calcium,andchromiumThis1.69percentmayseem
insignificant,butitsmassisstill5,628timesthemassofEarth.
Thesunisnotasolidmass.Itdoesnothaveeasilyidentifiableboundarieslike
rockyplanetssuchasEarth.Instead,thesuniscomposedoflayersmadeup
almostentirelyofhydrogenandhelium.Thesegasescarryoutdifferentfunctions
ineachlayer,andthesun’slayersaremeasuredbytheirpercentageofthesun’s
totalradius.
Thesunispermeatedandsomewhatcontrolledbyamagneticfield.Themagnetic
fieldisproducedbyacombinationofthreecomplexmechanisms:acircular
electriccurrentthatrunsthroughthesun;layersofthesunthatrotateat
differentspeeds;andthesun’sabilitytoconductelectricity.Nearthesun’s
equator,magneticfieldlinesmakesmallloopsnearthesurface.Magneticfieldlines
thatflowthroughthepolesextendmuchfarther,thousandsofkilometers,before
returningtotheoppositepole.
Thesunrotatesarounditsownaxis,justlikeEarth.Thesunrotates
counterclockwise,andtakesbetween25and35daystocompleteasingle
rotation.
ThesunorbitsclockwisearoundthecenteroftheMilkyWay.Itsorbitisbetween
24,000and26,000light-yearsawayfromthegalacticcenter.Thesuntakesabout
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225millionto250millionyearstoorbitonetimearoundthegalacticcenter.
ElectromagneticRadiation
Thesun’senergytravelstoEarthatthespeedoflightintheformof
electromagneticradiation(EMR).
Theelectromagneticspectrumexistsaswavesofdifferentfrequenciesand
wavelengths.Thefrequencyofawaverepresentshowmanytimesthewave
repeatsitselfinacertainunitoftime.Waveswithveryshortwavelengthsrepeat
themselvesseveraltimesinagivenunitoftime,sotheyarehigh-frequency.In
contrast,low-frequencywaveshavemuchlongerwavelengths.
Thevastmajorityofelectromagneticwavesthatcomefromthesunareinvisibleto
us.Themosthigh-frequencywavesemittedbythesunaregammarays,X-rays,
andultravioletradiation(UVrays).ThemostharmfulUVraysarealmost
completelyabsorbedbyEarth’satmosphere.LesspotentUVraystravelthrough
theatmosphere,andcancausesunburn.
Thesunalsoemitsinfraredradiation,whosewavesaremuchlower-frequency.
Mostheatfromthesunarrivesasinfraredenergy.
SandwichedbetweeninfraredandUVisthevisiblespectrum,whichcontainsall
thecolorsweseeonEarth.Thecolorredhasthelongestwavelengths(closestto
infrared),andviolet(closesttoUV)theshortest.
Thesunitselfiswhite,whichmeansitcontainsallofthecolorsinthevisible
spectrum.Thesunappearsorange-ishyellowbecausethebluelightitemitshasa
shorterwavelength,andisscatteredintheatmosphere—thesameprocessthat
makestheskyappearblue.
Astronomers,however,callthesuna“yellowdwarf”starbecauseitscolorsfall
withintheyellow-greensectionoftheelectromagneticspectrum.
EvolutionoftheSun
Thesun,althoughithassustainedalllifeonourplanet,willnotshineforever.The
sunhasalreadyexistedforabout4.5billionyears.
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Theprocessofnuclearfusion,whichcreatestheheatandlightthatmakelifeon
ourplanetpossible,isalsotheprocessthatslowlychangesthesun’scomposition.
Throughnuclearfusion,thesunisconstantlyusingupthehydrogeninitscore:
Everysecond,thesunfusesaround620millionmetrictonsofhydrogeninto
helium.
Atthisstageinthesun’slife,itscoreisabout74%hydrogen.Overthenext5
billionyears,thesunwillburnthroughmostofitshydrogen,andheliumwill
becomeitsmajorsourceoffuel.
Overthose5billionyears,thesunwillgofrom“yellowdwarf”to“redgiant.”
Whenalmostallofthehydrogeninthesun’scorehasbeenconsumed,thecore
willcontractandheatup,increasingtheamountofnuclearfusionthattakesplace.
Theouterlayersofthesunwillexpandfromthisextraenergy.
Thesunwillexpandtoabout200timesitscurrentradius,swallowingMercuryand
Venus.AstrophysicistsdebatewhetherEarth’sorbitwouldexpandbeyondthe
sun’sreach,orifourplanetwouldbeengulfedbythesunaswell.
Asthesunexpands,itwillspreaditsenergyoveralargersurfacearea,whichhas
anoverallcoolingeffectonthestar.Thiscoolingwillshiftthesun’svisiblelighttoa
reddishcolor—aredgiant.
Eventually,thesun’scorereachesatemperatureofabout100milliononthe
Kelvinscale,thecommonscientificscaleformeasuringtemperature.Whenit
reachesthistemperature,heliumwillbeginfusingtocreatecarbon,amuch
heavierelement.Thiswillcauseintensesolarwindandothersolaractivity,which
willeventuallythrowofftheentireouterlayersofthesun.Theredgiantphasewill
beover.Onlythesun’scarboncorewillbeleft,andasa“whitedwarf,”itwillnot
createoremitenergy.
Sun’sStructure
Thesunismadeupofsixlayers:core;radiativezone;convectivezone;
photosphere;chromosphere;andcorona.
Core
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Thesun’score,morethanathousandtimesthesizeofEarthandmorethan10
timesdenserthanlead,isahugefurnace.Temperaturesinthecoreexceed15.7
millionKelvin(also15.7milliondegreesCelsius,or28milliondegreesFahrenheit).
Thecoreextendstoabout25%ofthesun’sradius.
Thecoreistheonlyplacewherenuclearfusionreactionscanhappen.Thesun’s
otherlayersareheatedfromthenuclearenergycreatedthere.Protonsof
hydrogenatomsviolentlycollideandfuse,orjointogether,tocreateahelium
atom.
Thisprocess,knownasaPP(proton-proton)chainreaction,emitsanenormous
amountofenergy.Theenergyreleasedduringonesecondofsolarfusionisfar
greaterthanthatreleasedintheexplosionofhundredsofthousandsofhydrogen
bombs.
Duringnuclearfusioninthecore,twotypesofenergyarereleased:photonsand
neutrinos.Theseparticlescarryandemitthelight,heat,andenergyofthesun.
Photonsarethesmallestparticleoflightandotherformsofelectromagnetic
radiation.Neutrinosaremoredifficulttodetect,andonlyaccountforabout2%of
thesun’stotalenergy.Thesunemitsbothphotonsandneutrinosinalldirections,
allthetime.
RadiativeZone
Theradiativezoneofthesunstartsatabout25%oftheradius,andextendsto
about70%oftheradius.Inthisbroadzone,heatfromthecorecools
dramatically,frombetween7millionto2millionK.
Intheradiativezone,energyistransferredbyaprocesscalledthermalradiation.
Duringthisprocess,photonsthatwerereleasedinthecoretravelashort
distance,areabsorbedbyaclose-byion,releasedbythation,andabsorbedagain
byanother.Onephotoncancontinuethisprocessforalmost200,000years!
Aneutrino’stripthroughtheradiativezoneandtherestofthesun’slayersis
muchquicker:Inabout2.3seconds,neutrinospassthroughmorethan643,738
kilometers(400,000miles)ofthesun’slayers.NeutrinosaimedatEartheasily
passthroughEarth’satmosphere,water,land,ice,animals,plants,andhumans.
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Thisispossiblebecauseneutrinosdonotcarryanelectriccharge.Theydonot
interactwithmostparticlesthattheycomeincontactwith.
TransitionZone:Tachocline
Betweentheradiativezoneandthenextlayer,theconvectivezone,thereisa
transitionzonecalledthetachocline.Thisregioniscreatedasaresultofthesun’s
differentialrotation.
Differentialrotationhappenswhendifferentpartsofanobjectrotateatdifferent
velocities.Thesunismadeupofgasesundergoingdifferentprocessesat
differentlayersanddifferentlatitudes.Thesun’sequatorrotatesmuchfasterthan
itspoles,forinstance.
Therotationrateofthesunchangesrapidlyinthetachocline.
ConvectiveZone
Ataround70%ofthesun’sradius,theconvectivezonebegins.Inthiszone,the
sun’stemperatureisnothotenoughtotransferenergybythermalradiation.
Instead,ittransfersheatbythermalconvectionthroughthermalcolumns.
Similartowaterboilinginapot,orhotwaxinalavalamp,gasesdeepinthesun’s
convectivezoneareheatedand“boil”outward,awayfromthesun’score,
throughthermalcolumns.Whenthegasesreachtheouterlimitsoftheconvective
zone,theycooldown,andplungebacktothebaseoftheconvectivezone,tobe
heatedagain.
Photosphere
Thephotosphereisthebrightyellow,visible"surface"ofthesun.Thephotosphere
isabout400kilometers(250miles)thick,andtemperaturestherereachabout
6,000K(5,700°C,10,300°F).
Thethermalcolumnsoftheconvectionzonearevisibleinthephotosphere,
bubblinglikeboilingoatmeal.Throughpowerfultelescopes,thetopsofthe
columnsappearasgranulescrowdedacrossthesun.Eachgranulehasabright
center,whichisthehotgasrisingthroughathermalcolumn.Thegranules’dark
edgesarethecoolgasdescendingbackdownthecolumntothebottomofthe
convectivezone.
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Althoughthetopsofthethermalcolumnslooklikesmallgranules,theyareusually
morethan1,000kilometers(621miles)across.Mostthermalcolumnsexistfor
about8to20minutesbeforetheydissolveandformnewcolumns.Therearealso
“supergranules”thatcanbeupto30,000kilometers(18,641miles)across,and
lastforupto24hours.
Thesunisconstantlycoveredbyabout4,000granules.
Sunspots,solarflares,andsolarprominencestakeforminthephotosphere,
althoughtheyaretheresultofprocessesanddisruptionsinotherlayersofthe
sun.
Photosphere:Sunspots
Asunspotisjustwhatitsoundslike—adarkspotonthesun.Asunspotforms
whenintensemagneticactivtiyintheconvectivezonerupturesathermalcolumn.
Atthetopoftherupturedcolumn(visibleinthephotosphere),temperatureis
temporarilydecreasedbecausehotgasesarenotreachingit.Thiscooler
temperature(still6,000K,or2,727°C,or4,940°F)causesthetopofthecolumn
toappearmuchdarkerthanthesurroundingarea.
Photosphere:SolarFlares
Theprocessofcreatingsunspotsopensaconnectionbetweenthecorona(the
veryouterlayerofthesun)andthesun’sinterior.Solarmattersurgesoutofthis
openinginformationscalledsolarflares.Theseexplosionsaremassive:Inthe
periodofafewminutes,solarflaresreleasetheequivalentofabout160billion
megatonsofTNT,oraboutasixthofthetotalenergythesunreleasesinone
second.
Cloudsofions,atoms,andelectronseruptfromsolarflares,andreachEarthin
abouttwodays.Solarflaresandsolarprominencescontributetospaceweather,
whichcancausedisturbancestoEarth’satmosphereandmagneticfield,aswell
asdisruptsatelliteandtelecommunicationssystems.
Photosphere:CoronalMassEjections
Coronalmassejections(CMEs)areanothertypeofsolaractivitycausedbythe
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constantmovementanddisturbanceswithinthesun’smagneticfield.Eruptions
fromCMEstravelfrom20to3,200kilometers(12to2,000miles)persecond.
AlthoughCMEstypicallyformneartheactiveregionsofsunspots,thecorrelation
betweenthetwohasnotbeenproven.ThecauseofCMEsisstillbeingstudied,
anditishypothesizedthatdisruptionsineitherthephotosphereorcoronaleadto
theseviolentsolarexplosions.
Photosphere:SolarProminence
Solarprominencesarebrightloopsofsolarmatter.Theycanburstfarintothe
coronallayerofthesun,expandinghundredsofkilometerspersecond.These
curvedandtwistedfeaturescanreachhundredsofthousandsofkilometersin
heightandwidth,andlastanywherefromafewdaystoafewmonths.
Solarprominencesarecoolerthanthecorona,andtheyappearasdarkerstrands
againstthesun.Forthisreason,theyarealsoknownasfilaments.
Photosphere:SolarCycle
Thesundoesnotconstantlyemitsunspotsandsolarejecta;itgoesthrougha
cycleofabout11years.Duringthissolarcycle,thefrequencyofsolarflares
changes.Duringsolarmaximums,therecanbeseveralflaresperday.During
solarminimums,theremaybefewerthanoneaweek.
Thesolarcycleisdefinedbythesun’smagneticfields,whichlooparoundthesun
andconnectatthetwopoles.Every11years,themagneticfieldsreverse,causing
adisruptionthatleadstosolaractivityandsunspots.
ThesolarcyclecanhaveeffectsonEarth’sclimate.Forexample,thesun’s
ultravioletlightsplitsoxygeninthestratosphereandstrengthensEarth’s
protectiveozonelayer.Duringthesolarminimum,therearelowamountsofUV
rays,whichmeansthatEarth’sozonelayeristemporarilythinned.Thisallows
moreUVraystoenterandheattheEarth’satmosphere.
SolarAtmosphere
Thesolaratmosphereisthehottestregionofthesun.Itismadeupofthe
chromosphere,thecorona,andatransitionzonecalledthesolartransitionregion
thatconnectsthetwo.
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Thesolaratmosphereisobscuredbythebrightlightemittedbythephotosphere,
anditcanrarelybeseenwithoutspecialinstruments.Onlyduringsolareclipses,
whenthemoonmovesbetweentheEarthandthesunandhidesthephotosphere,
cantheselayersbeseenwiththeunaidedeye.
Chromosphere
Thepinkish-redchromosphereisabout2,000kilometers(1,250miles)thickand
riddledwithjetsofhotgas.
Atthebottomofthechromosphere,whereitmeetsthephotosphere,thesunis
atitscoolest,atabout4,400K(4,100°C,7,500°F).Thislowtemperaturegives
thechromosphereitspinkcolor.Thetemperatureinthechromosphereincreases
withaltitude,andreaches25,000K(25,000°C,45,000°F)attheouteredgeof
theregion.
Thechromospheregivesoffjetsofburninggasescalledspicules,similartosolar
flares.Thesefierywispsofgasreachoutfromthechromospherelikelong,
flamingfingers;theyareusuallyabout500kilometers(310miles)indiameter,and
moveoutwardfromthesunatabout20kilometers(12miles)persecond.
Spiculesonlylastforabout15minutes,butcanreachthousandsofkilometersin
heightbeforecollapsinganddissolving.
SolarTransitionRegion
Thesolartransitionregion(STR)separatesthechromospherefromthecorona.
BelowtheSTR,thelayersofthesunarecontrolledandstayseparatebecauseof
gravity,gaspressure,andthedifferentprocessesofexchangingenergy.Above
theSTR,themotionandshapeofthelayersaremuchmoredynamic.Theyare
dominatedbymagneticforces.Thesemagneticforcescanputintoactionsolar
eventssuchascoronalloopsandthesolarwind.
Thestateofheliuminthesetworegionshasdifferencesaswell.BelowtheSTR,
heliumispartiallyionized.Thismeansitstillhasoneelectron.AroundtheSTR,
heliumabsorbsabitmoreheatandlosesitslastelectron.Itstemperaturesoars
toalmost1millionK(1million°C,1.8million°F).
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Corona
Thecoronaisthewispyoutermostlayerofthesolaratmosphere,andcanextend
millionsofkilometersintospace.Gasesinthecoronaburnatabout1millionK(1
million°C,1.8million°F),andmoveabout145kilometers(90miles)persecond.
Someoftheparticlesreachanescapevelocityof400kilometerspersecond(249
milespersecond).Theyescapethesun’sgravitationalpullandbecomethesolar
wind.Thesolarwindblastsfromthesuntotheedgeofthesolarsystem.
Otherparticlesformcoronalloops.Coronalloopsareburstsofparticlesthat
curvebackaroundtoanearbysunspot.
Nearthesun’spolesarecoronalholes.Theseareasarecolderanddarkerthan
otherregionsofthesun,andallowsomeofthefastest-movingpartsofthesolar
windtopassthrough.
Electromagneticradiationthatescapesfromthecoronaisclassifiedintothree
types:K-corona,F-corona,andE-corona.
ThelightfromtheK-coronacomesfromsunlightscatteringfreeelectrons.Light
fromtheF-coronaiscausedbysunlightbouncingoffofcosmicdustparticles.
LightfromtheE-coronaresultsfromchangesinthequantityofphotonsinan
otherwiseuniformarea.TheE-coronasuppliesinformationaboutthecorona’s
composition.
SolarWind
Thesolarwindisastreamofextremelyhot,chargedparticlesthatarethrownout
fromtheupperatmosphereofthesun.Enormousamountsofmaterialare
releasedfromthesun:about4-6billionmetrictonseveryhour.Thismeansthat
every150millionyears,thesunlosesamassequaltothatoftheEarth.However,
evenatthisrateofloss,thesunhasonlylostabout0.01%ofitstotalmassfrom
solarwind.
Thesolarwindblowsinalldirections,atabout1millionkph(620,000mph).It
continuesmovingatthatspeedforabout10billionkilometers(6billionmiles).
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SomeoftheparticlesinthesolarwindslipthroughEarth’smagneticfieldandinto
itsupperatmospherenearthepoles.Astheycollidewithatmosphere,these
chargedparticlessettheatmosphereaglowwithcolor,creatingauroras,colorful
lightdisplaysknownastheNorthernandSouthernLights.Solarwindscanalso
causesolarstorms.Thesestormscaninterferewithsatellitesandknockout
powergridsonEarth.
Thesolarwindfillstheheliosphere,themassivebubbleofchargedparticlesthat
encompassesthesolarsystem.
Thesolarwindeventuallyslowsdownneartheborderoftheheliosphere,ata
theoreticalboundarycalledtheheliopause.Thisboundaryseparatesthematter
andenergyofoursolarsystemfromthematterinneighboringstarsystemsand
theinterstellarmedium.
Theinterstellarmediumisthespacebetweenstarsystems.Thesolarwind,having
traveledbillionsofkilometers,cannotextendbeyondtheinterstellarmedium.
StudyingtheSun
Thesunhasnotalwaysbeenasubjectofscientificdiscoveryandinquiry.For
thousandsofyears,thesunwasknowninculturesallovertheworldasagod,a
goddess,andasymboloflife.
TotheancientAztecs,thesunwasapowerfuldeityknownasTonatiuh,who
requiredhumansacrificetotravelacrossthesky.InBalticmythology,thesunwas
agoddessnamedSaule,whobroughtfertilityandhealth.Chinesemythologyheld
thatthesunistheonlyremainingof10sungods.
In150CE,GreekscholarClaudiusPtolemycreatedageocentricmodelofthesolar
systeminwhichthemoon,planets,andsunrevolvedaroundtheEarth.Thiswas
themodelforalmost1,200years,reachingpeopleinWesternEurope,North
Africa,andtheMiddleEast.
Itwasnotuntilthe16thcenturythatPolishastronomerNicolausCopernicusused
mathematicalandscientificreasoningtoprovethatplanetsrotatedaroundthe
sun.Thisheliocentricmodelistheoneweusetoday.
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Inthe17thcentury,thetelescopeallowedpeopletoexaminethesunindetail.The
sunismuchtoobrighttoallowustostudyitwithoureyesunprotected.Witha
telescope,itwaspossibleforthefirsttimetoprojectaclearimageofthesunonto
ascreenforexamination.
EnglishscientistSirIsaacNewtonusedatelescopeandprismtoscatterthelight
ofthesun,andprovedthatsunlightwasactuallymadeofaspectrumofcolors.
In1800,infraredandultravioletlightwerediscoveredtoexistjustoutsideofthe
visiblespectrum.Anopticalinstrumentcalledaspectroscopemadeitpossibleto
separatevisiblelightandotherelectromagneticradiationintoitsvarious
wavelengths.Spectroscopyalsohelpedscientistsidentifygasesinthesun’s
atmosphere—eachelementhasitsownwavelengthpattern.
However,themethodbywhichthesungenerateditsenergyremainedamystery.
Manyscientistshypothesizedthatthesunwascontracting,andemittingheat
fromthatprocess.
In1868,EnglishastronomerJosephNormanLockyerwasstudyingthesun’s
electromagneticspectrum.Heobservedbrightlinesinthephotospherethatdid
nothaveawavelengthofanyknownelementonEarth.Heguessedthattherewas
anelementisolatedonthesun,andnameditheliumaftertheGreeksungod,
Helios.
Lockyer’sdiscoveryrevolutionizedsolarscience.Overthenext30years,
astronomersconcludedthatthesunhadahot,pressurizedcorethatwascapable
ofproducingmassiveamountsofenergythroughnuclearfusion.
Technologycontinuedtoimproveandallowedscientiststouncovernewfeatures
ofthesun.Infraredtelescopeswereinventedinthe1960s,andscientists
observedenergyoutsideofthevisiblespectrum.Twentieth-centuryastronomers
usedballoonsandrocketstosendspecializedtelescopeshighabovetheEarth,
andexaminedthesunwithoutanyinterferencefromtheEarth'satmosphere.
Solrad1wasthefirstspacecraftdesignedtostudythesun,andwaslaunchedby
theUnitedStatesin1960.Thatdecade,NASAsentfivePioneersatellitestoorbit
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thesunandcollectinformationaboutthestar.
In1980,NASAlaunchedamissionduringthesolarmaximumtogather
informationaboutthehigh-frequencygammarays,UVrays,andX-raysthatare
emittedduringsolarflares.
TheSolarandHeliosphericObservatory(SOHO)wasdevelopedinEuropeandput
intoorbitin1996tocollectinformation.SOHOhasbeensuccessfullycollecting
dataandforecastingspaceweatherfor12years.
Voyager1and2arespacecrafttravelingtotheedgeoftheheliosphereto
discoverwhattheatmosphereismadeofwheresolarwindmeetstheinterstellar
medium.Bothspacecraftarescheduledtoreachthisboundaryin2014!
Anotherdevelopmentinthestudyofthesunishelioseismology,thestudyofsolar
waves.Theturbulenceoftheconvectivezoneishypothesizedtocontributeto
solarwavesthatcontinuouslytransmitsolarmaterialtotheouterlayersofthe
sun.Bystudyingthesewaves,scientistsunderstandmoreaboutthesun’sinterior
andthecauseofsolaractivity.
EnergyfromtheSun
Photosynthesis
Sunlightprovidesnecessarylightandenergytoplantsandotherproducersinthe
foodweb.Theseproducersabsorbthesun’sradiationandconvertitintoenergy
throughaprocesscalledphotosynthesis.
Producersaremostlyplants(onland)andalgae(inaquaticregions).Theyarethe
foundationofthefoodweb,andtheirenergyandnutrientsarepassedontoevery
otherlivingorganism.
FossilFuels
PhotosynthesisisalsoresponsibleforallofthefossilfuelsonEarth.Scientists
estimatethatabout3,000millionyearsago,thefirstproducersevolvedinaquatic
settings.Sunlightallowedplantlifetothriveandadapt.Aftertheplantsdied,they
decomposedandshifteddeeperintotheEarth,sometimesthousandsofmeters.
Thisprocesscontinuedformillionsofyears.
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Underintensepressureandhightemperatures,theseremainsbecamewhatwe
knowasfossilfuels.Thesemicroorganismsbecamepetroleum,naturalgas,and
coal.
Peoplehavedevelopedprocessesforextractingthesefossilfuelsandusingthem
forenergy.However,fossilfuelsareanonrenewableresource.Theytakemillions
ofyearstoform.
SolarEnergyTechnology
Solarenergytechnologyharnessesthesun’sradiationandconvertsitintoheat,
light,orelectricity.
Solarenergyisarenewableresource,andmanytechnologiescanharvestit
directlyforuseinhomes,businesses,schools,andhospitals.Somesolarenergy
technologiesincludesolarvoltaiccellsandpanels,solarthermalcollectors,solar
thermalelectricity,andsolararchitecture.
Photovoltaicsusethesun’senergytospeedupelectronsinsolarcellsand
generateelectricity.Thisformoftechnologyhasbeenusedwidely,andcan
provideelectricityforruralareas,largepowerstations,buildings,andsmaller
devicessuchasparkingmetersandtrashcompactors.
Thesun’senergycanalsobeharnessedbyamethodcalled“concentratedsolar
power,”inwhichthesun’sraysarereflectedandmagnifiedbymirrorsandlenses.
Theintensifiedrayofsunlightheatsafluid,whichcreatessteamandpowersan
electricgenerator.
Solarpowercanalsobecollectedanddistributedwithoutmachineryor
electronics.Forexample,roofscanbecoveredwithvegetationorpaintedwhiteto
decreasetheamountofheatabsorbedintothebuilding,therebydecreasingthe
amountofelectricityneededforairconditioning.Thisissolararchitecture.
Sunlightisabundant:Inonehour,theEarth’satmospherereceivesenough
sunlighttopowertheelectricityneedsofallpeopleforayear.However,solar
technologyisexpensive,anddependsonsunnyandcloudlesslocalweathertobe
effective.Methodsofharnessingthesun’senergyarestillbeingdevelopedand
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improved.
Vocabulary
Term
Partof
Speech
astronomer
noun
astronomical
unit
noun
Definition
personwhostudiesspaceandtheuniversebeyond
Earth'satmosphere.
(AU)(150millionkilometers/93millionmiles)unitof
distanceequaltotheaveragedistancebetweenthe
Earthandthesun.
brightlycoloredbandsoflight,visiblearoundEarth's
geomagneticpoles,causedbysolarwindinteractingwith
particlesinEarth'smagneticfield.
transparentlayerofgassurroundingthephotosphere
(visibledisc)ofastar.
allweatherconditionsforagivenlocationoveraperiod
oftime.
topresstogetherinasmallerspace.
aurora
noun
chromosphere
noun
climate
noun
compress
verb
convection
noun
core
noun
corona
coronalmass
ejection
noun
transferofheatbythemovementoftheheatedpartsof
aliquidorgas.
theextremelyhotcenterofEarth,anotherplanet,ora
star.
outermostpartofthesunoranotherstar'satmosphere.
noun
hugeburstofsolarwindandotherchargedparticles.
dense
differential
rotation
dust
electricity
havingpartsormoleculesthatarepackedclosely
adjective
together.
patternwheredifferentpartsofanobjectrotateat
noun
differentspeedsorvelocities.
microscopicparticlesofrocksormineralsdriftingin
noun
space.Alsocalledcosmicdustorspacedust.
setofphysicalphenomenaassociatedwiththepresence
noun
andflowofelectriccharge.
electromagnetic
noun
spectrum
continousbandofallkindsofradiation(heatandlight).
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Term
Equator
Partof
Speech
noun
escapevelocity noun
foodweb
noun
fossilfuel
noun
frequency
noun
galaxy
noun
generator
noun
granule
noun
gravitational
pull
noun
heliopause
noun
helioseismology noun
infrared
radiation
interstellar
medium
noun
noun
ionize
verb
IsaacNewton
noun
Kelvinscale
noun
magneticfield
noun
Definition
imaginarylinearoundtheEarth,anotherplanet,orstar
runningeast-west,0degreeslatitude.
speedandforcethatanobjectmusthavetoescapethe
gravityofalargerbody,insteadoforbitingaroundit.
allrelatedfoodchainsinanecosystem.Alsocalleda
foodcycle.
coal,oil,ornaturalgas.Fossilfuelsformedfromthe
remainsofancientplantsandanimals.
rateofoccurrence,orthenumberofthingshappening
inaspecificareaoverspecifictimeperiod.
collectionofstars,planets,gases,andothercelestial
bodiesboundtogetherbygravity.
machinethatconvertsonetypeofenergytoanother,
suchasmechanicalenergytoelectricity.
topofaconvectivecellonthesun'sphotosphere,where
hotgasesriseandquicklydissipate.
physicalattractionbetweentwomassiveobjects.
outerboundaryofthesolarsystem,wherethesolar
windisstoppedbytheinterstellarmedium.
studyofthesun'sinteriorbyanalysisofthe(mostly
acoustic)wavesitemits.
partoftheelectromagneticspectrumwithwavelengths
longerthanvisiblelightbutshorterthanmicrowaves.
materialinthespacebetweenstarsystems,mostly
hydrogenplasmaandcosmicdust.
toaddorremoveanelectrontoanatomorgroupof
atoms,givingthemanelectriccharge.
(1642-1727)Englishphysicist,mathematician,and
philosopher.
scaleformeasuringtemperaturewherezeroKelvinis
absolutezero,theabsenceofallenergy.
areaaroundandaffectedbyamagnetorcharged
particle.
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Term
Partof
Speech
Definition
molecularcloud noun
regionofgas,plasma,andcosmicdustwheremolecules
(usuallymolecularhydrogen)form.
neutrino
noun
subatomicparticlethatcarriesnoelectricalchargeand
interactsweaklywithallothermatter.
nonrenewable
resource
noun
naturalresourcethatexistsinalimitedsupply.
nuclearfusion
noun
processwherethenucleiofoneelement,usually
hydrogen,fusewitheachothertoformthenucleiof
anotherelement,usuallyhelium.
nutrient
noun
orbit
noun
ozonelayer
noun
photon
noun
photosphere
noun
photosynthesis noun
photovoltaic
noun
powergrid
noun
radiativezone
noun
radius
noun
redgiant
noun
resource
rotate
whichthestar'sdiameterismeasured.
processbywhichplantsturnwater,sunlight,and
carbondioxideintowater,oxygen,andsimplesugars.
adjectiveabletoconvertsolarradiationtoelectricalenergy.
plasma
renewable
substanceanorganismneedsforenergy,growth,and
life.
pathofoneobjectaroundamoremassiveobject.
layerintheatmospherecontainingthegasozone,which
absorbsmostofthesun'sultravioletradiation.
smallestunitoflight,orelectromagneticradiation.
lowestvisiblelayerofastarandtheboundaryfrom
noun
verb
stateofmatterwithnofixedshapeandmolecules
separatedintoionsandelectrons.
networkofcablesorotherdevicesthroughwhich
electricityisdeliveredtoconsumers.Alsocalledan
electricalgrid.
areaofastar'sinteriorwhereenergyistransferred
throughthermalradiation.
rayextendingfromthecenterofacircleorspheretoits
surfaceorcircumference.
"mainsequence"starwithhugesurfacearea,low
surfacetemperature,andreddishcolor.
resourcethatcanreplenishitselfatasimilarratetoits
usebypeople.
toturnaroundacenterpointoraxis.
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Term
rupture
satellite
solar
architecture
solarcycle
Partof
Definition
Speech
verb
tobreakortear.
objectthatorbitsaroundsomethingelse.Satellitescan
noun
benatural,likemoons,ormadebypeople.
theplanninganddesignofbuildingstomakethemost
noun
useofthesun'sheatandlight.
fairlypredictablechangesinsolaractivity(suchas
noun
sunspotsandsolarflares)overan11-yearperiod.
solareclipse
noun
solarenergy
noun
solarflare
noun
solar
prominence
noun
solarstorm
noun
solarsystem
noun
solarwind
noun
spaceweather noun
spectroscopy
noun
spicule
noun
star
noun
sunspot
noun
supernova
noun
eventwhenthesunisblockedbythemoonpassing
betweenitandtheEarth.
radiationfromthesun.
explosioninthesun'satmosphere,whichreleasesa
burstofenergyandchargedparticlesintothesolar
system.
hugeeruptionofcoolgasesfromthesurfaceofthe
sun,oftenshapedlikeagiantloop.
suddenchangeintheEarth'smagnetosphere,caused
bythesolarwindinteractingwiththeEarth'smagnetic
field.Alsocalledageomagneticstorm.
thesunandtheplanets,asteroids,comets,andother
bodiesthatorbitaroundit.
flowofchargedparticles,mainlyprotonsandelectrons,
fromthesuntotheedgeofthesolarsystem.
changesintheenvironmentoutsidetheEarth's
atmosphere,usuallyinfluencedbythesun.
scienceofthemeasurementoflightthatisreflected,
absorbed,oremittedbydifferentmaterials.
thin,dynamicjetofsolarmaterialejectedfromthe
chromosphere(upperatmosphere)ofthesun.
largeballofgasandplasmathatradiatesenergy
throughnuclearfusion,suchasthesun.
dark,coolerareaonthesurfaceofthesunthatcan
move,change,anddisappearovertime.
sudden,violentexplosionofamassivestar.
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Term
tachocline
Partof
Speech
noun
transitionzone noun
ultraviolet
radiation
noun
wavelength
noun
whitedwarf
noun
Definition
transitionzoneinthesun,betweeninner,radiativezone
andtheouter,convectivezone.
areabetweentwonaturalorartificialregions.
powerfullightwavesthataretooshortforhumansto
see,butcanpenetrateEarth'satmosphere.Ultravioletis
oftenshortenedtoUV.
thedistancebetweenthecrestsoftwowaves.
small,dense"mainsequence"starthathasusedup
mostofitsnuclearfuel.
Articles&Profiles
NationalGeographicNews:SunisRoundestNaturalObjectKnown
Images
NationalGeographicScience:SunPhotos
Video
NationalGeographicVideo:Sun101
Websites
NationalGeographicScience:TheSun—LivingWithaStormyStar
NASA:SolarSystemExploration—Sun
NASA:SolarandHeliosphericObservatory(SOHO)
NASA:Heliophysics
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