Aurora极光简介

HuifengGengDefinitionandCauseImagesColorsMythologyContentsAnauroraisanaturallightdisplayinthesky(fromtheLatinwordaurora,“sunrise”ortheRomangoddessofdawn),predominantlyseeninthehighlatitude(ArcticandAntarctic)regions.DefinitionandCause•DefinitionAuroraearecausedbycosmicrays（宇宙辐射线）,solarwindandmagnetosphericplasma（磁能层的等离子体）interactingwiththeupperatmosphere(thermosphere（热大气层）/exosphere（外大气层）).Theirchargedparticles（带电粒子）,mainlyelectrons（电子）andprotons（质子）,entertheatmospherefromabovecausingionization（电离）andexcitationofatmosphericconstituents,andconsequentlightemissions（发光）.Incidentprotonscanalsoproduceemissionsashydrogenatomsaftergaininganelectronfromtheatmosphere.DefinitionandCause•CauseImagesThealtitudeswhereauroraemissionsoccurwererevealedbyCarlStørmerandhiscolleagueswhousedcamerastotriangulatemorethan12,000aurorae.Theydiscoveredthatmostofthelightisproducedbetween90and150kmabovetheground,whileextendingattimestomorethan1000km.Imagesofaurorasaresignificantlymorecommontodaythaninthepastduetotheincreaseinuseofdigitalcamerasthathavehighenoughsensitivities.Filmanddigitalexposuretoauroraldisplaysisfraughtwithdifficulties,particularlyiffaithfulnessofreproductionisanobjective.Duetothedifferentcolorspectrumpresent,andthetemporalchangesoccurringduringtheexposure,theresultsaresomewhatunpredictable.Differentlayersofthefilmemulsionresponddifferentlytolowerlightlevels,andchoiceoffilmcanbeveryimportant.Longerexposuressuperimposerapidlychangingfeatures,andoftenblanketthedynamicattributeofadisplay.Highersensitivitycreatesissueswithgraininess.01020304ColorRedGreenYellowandPinkBlueAtthehighestaltitudes,excitedatomicoxygenemitsat630.0nm(red);lowconcentrationofatomsandlowersensitivityofeyesatthiswavelengthmakethiscolorvisibleonlyundermoreintensesolaractivity.Thelowamountofoxygenatomsandtheirgraduallydiminishingconcentrationisresponsibleforthefaintappearanceofthetoppartsofthecurtains.Scarlet,crimson,andcarminearethemostoften-seenhuesofredfortheaurorae.Atloweraltitudesthemorefrequentcollisionssuppressthe630.0nm(red)mode:ratherthe557.7nmemission(green)dominates.Fairlyhighconcentrationofatomicoxygenandhighereyesensitivityingreenmakegreenaurorasthemostcommon.Theexcitedmolecularnitrogen(atomicnitrogenbeingrareduetohighstabilityoftheN2molecule)playsitsrolehereaswell,asitcantransferenergybycollisiontoanoxygenatom,whichthenradiatesitawayatthegreenwavelength.(Redandgreencanalsomixtogethertoproducepinkoryellowhues.)Therapiddecreaseofconcentrationofatomicoxygenbelowabout100kmisresponsiblefortheabrupt-lookingendoftheloweredgesofthecurtains.Yellowandpinkareamixofredandgreenorblue.Othershadesofredaswellasorangemaybeseenonrareoccasions;yellow-greenismoderatelycommon.Asred,green,andbluearetheprimarycolorsofadditivesynthesis（合成）ofcolors,intheorypracticallyanycolormightbepossible.Atyetloweraltitudes,atomicoxygenisuncommon,andionizedmolecularnitrogentakesoverinproducingvisiblelightemission;itradiatesatalargenumberofwavelengthsinbothredandbluepartsofthespectrum,with428nm(blue)beingdominant.Blueandpurpleemissions,typicallyattheloweredgesofthecurtains,showupatthehighestlevelsofsolaractivity.TheValkyrior（瓦尔基里）arewarlikevirgins,mounted（骑上）uponhorsesandarmedwithhelmetsandspears.Whentheyrideforthontheirerrand（使命）,theirarmourshedsastrangeflickeringlight,whichflashesupoverthenorthernskies,makingwhatMencalltheauroraborealis,orNorthernLights.TheValkyriorFamousAurorastendtobefromSpanishspeakingcountries.ActressesincludeAuroraClavelandAuroraBautista.AuthorsincludeAuroraCaceresandAuroraLevinsMorales.AuroraReyesFloreswasamemberofthemuralistmovementandAuroraEstradaOrozcowasaMexicanAmericancommunityleader.FamouspersonsnamedAurora