Therainbowisaverycommonphenomenonofphysicaloptics.Usuallywhenwewillappearinthesunshineaftertheraintoseetheskyabove,colorfulspectrum,willbetheformationofvaultedcurvedshapes,verybrightcolors.Youknowwhytherainbowisformed?Howistherainbowformed? 　　Infact,aslongasthewaterdropletsintheair,andthesunisbehindtheobserveratalowangleradiation,mayproducetherainbowphenomenoncanbeobserved.Therainbowisbecausesunlightnearlyroundairdroplets,resultingindispersionandreflectionlightinto.Thesunlightwillalsodropunderdifferentincidentangle,withinthewaterdropletsistoreflectthedifferentangle.Withthereflectionbetween40to42degreeisthemostintense,theformationofpeoplemayseetherainbow.Therainbowaftertherainintheafternoonappearsmostoften,justturnwhentheweatherisfine.Whentheairinlessdustandfullofsmallwaterdroplets,theskysidebecausetherearestillcloudsanddark.Andtheobserverhasnoheadorbehindthecloudocclusionsvisiblesunlight,itwillbeeasiertobeseenrainbow. 　　Thegeneralappearanceoftherainbowiscloselyrelatedwiththeweather,peoplefromtherainbowappearsintheskypositioncanbepresumedthattherewillbesunnyorrainydays.Iftherainbowappearsintheeastern,thelocalwillnoteasilyrain,whilewesternrainbow,itwillhaveagreatpossibilitytorainlocal.