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1、WHYISTHESKYBLUE"Iseeskiesofblueandcloudsofwhite,"LouisArmstrongcroonedinhis1968song"WhataWonderfulWorld."Andheprobablydid,giventhathissongisanodetooptimism.Europeanresearchershavediscoveredthatlightfromthebluepartofthespectruminfluencestheemotionsinapositiveway,maki
2、ngusmoreresponsivetoemotionalstimuliandmoreadaptabletoemotionalchallenges[source:Opfocus].Butwedigress.Thereasontheskyappearsblueisbecauseofaneffectcalledscattering.SunlighthastopassthroughtheEarth'satmosphere,whichisfilledwithgasesandparticlesthatactlikethebumperso
3、napinballmachine,bouncingsunlightallovertheplace.Butifyou'veeverheldaprisminyourhands,youknowthatsunlightactuallyismadeupofabunchofdifferentcolors,allofwhichhavedifferentwavelengths.Bluelighthasarelativelyshortwavelength,soitgetsthroughthefiltermoreeasilythancolorsw
4、ithlongerwavelengths,andasaresultarescatteredmorewidelyastheypassthroughtheatmosphere.That'swhytheskylooksblueduringthepartsofthedaywhentheSunappearstobehighinthesky(thoughit'sactuallythespotontheplanetwhereyouarestandingthatismoving,relativetotheSun).HOWOLDISTHEEAR
5、THAtsunriseandsunset,though,thesun'srayshavetotravelalongerdistancetoreachyourposition.Thatcancelsoutbluelight'swavelengthadvantageandallowsustoseetheothercolorsbetter,whichiswhysunsetsoftenappearred,orangeoryellow[sources:NASA,ScienceDaily].TheEarth'sageissomething
6、thatpeoplehavebeenarguingabout,attimesbitterly,foralong,longtime.Backin1654,ascholarnamedJohnLightfoot,whosecalculationswerebasedupontheBookofGenesisintheBible,proclaimedthattheEarthhadbeencreatedatprecisely9a.m.Mesopotamiantime,onOct.26,4004B.C.Inthelate1700s,ascie
7、ntistnamedtheComtedeBuffonheatedupasmallreplicaoftheplanetthathehadcreatedandmeasuredtherateatwhichitcooled,andbaseduponthatdata,estimatedthattheEarthwasabout75,000yearsold.Inthe19thcentury,thephysicistLordKelvinuseddifferentequationstosettheEarth'sageat20to40millio
8、nyears[source:Badash].Butallthatwastrumpedinthelate1800sandearly1900sbythediscoveryofradioactivity,whichwassoonfollowedbycalculationofther
