TheMoonisEarth?closestneighbourinspace.ItsorbitaroundEarthiselliptical,ratherthancircular,whichmeansthatitsdistancefromusvaries.AtitsclosestpointstoEarth(itsperigee),theMoonis363,300kmaway.However,atitsfurthestdistancefromtheplanet(itsapogee)itis405,500kmaway.Incredibly,theMoon?orbitisslowlycarryingitawayfromEarthatarateofaround5cmayear.
WhatistheMoonmadeof?
AlthoughtheMoon?interiorstructureisdifficulttostudy,scientistsbelievethatithasasmallironcore.Surroundingthisisapartiallymoltenzonecalledthelowermantle.Abovethisliesthemantle,whichismadeupofrock,andthecrust,whichisalsomadeofrock.Together,themantleandthecrustformthelithosphere,whichcanbeupto800kmthick.ThereareonlytwobasicregionsontheMoon?surface—darkplainscalledmariaandlighterhighlands.TheseheavilycrateredhighlandsaretheoldestpartsoftheMoon?crust,datingbackoverfourbillionyears.Thedarkerplainsarecrateredthatwerefilledwithlava.
Whydowealwaysseethesamesideofthemoon?
TheMoontakesthesametimetorotateonitsaxisasitdoestoorbittheEarth.Becauseofthis,wealwaysseethesamesideoftheMoon.Thefarsideremainedamysterytoastronomersuntil1959,whentheRussianLuna3spaceprobetraveledbehindtheMoonandsentbackphotographs.
HowdoestheMoonaffectEarth?
DespitebeingmuchsmallerthantheEarth,theMoonstillhasagreatdealofinfluenceonitsparentplanet.ItsgravityisconstantlypullingonEarth?surface.Thisisnotnoticeableinrelationtosolidground,butcanclearlybeseeninthemovementofEarth?tides.Twiceaday,theoceansonEarthriseandfall.ThisisbecausetheMoon?gravitationalpullisstrongestonthesideifEarththatisfacingtheMoon.Oceansonthissidewillbepulledintoabulge—hightide.WaterontheoppositesideisleastaffectedbytheMoon?gravity,soitflowsawayfromEarthinanotherbulge,resultinginanotherhightide.AreasofEarthatrightanglestotheMoon,willhavelowtide.
IstheMoonhotorcold?
TheMoonexperiencestemperaturesbothhotterandcolderthanthoseonEarth.WhentheSunisdirectlyoverhead,thetemperatureontheMoon?surfaceishigherthantheboilingpointofwater—1000C.However,atnight,theMoonbecomesverycold,withtemperaturesdroppingto-1730C.EarthandtheMoonareapproximatelythesamedistancefromtheSun,andthereforereceivethesameamountofheat.ButthelackofanatmosphereontheMoonmeansthatitstemperaturerangeismuchmoreextreme.TheSun?radiationisnotfilteredoutbygasesintheatmosphere,andtherearenocloudstostopheatescapingatnight.
HowdidtheMoonfrom?
NobodyknowsexactlyhowtheMoonformed.ThemostcommontheoryisthatshortlyafterEarthformed,itwashitbyanobjectthesizeofMars.Theimpactwassopowerfulthatitsentbillionsoftonesofmoltenmaterialintospace.ThisdebriswasheldinorbitaroundEarth,andeventuallysolidifiedtoformtheMoon.
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