阅读理解
SometimesinthemonthofNovemberaspecialeventhappensintheskythatobserversmayrememberforalifetime.Theeventismorethanameteorshower(流星雨).Itisameteorstorm.
Meteorsarepiecesofrockfromspacethatburnupinouratmosphere(大气).MeteorshowershappenwhentheEarthpassesthroughalargeamountofspacematerialduringitsorbit(按轨道运行)aroundthesun.
Howeverthousandsofmeteorsfallduringameteorstorm.Someofthemmaybrieflyshinebrighterthananystarinthesky.
TheLeonidmeteorshowerhappenseveryNovember.Inmostyearsitisnotunusual.Leonidmeteorsfallatanaveragerateofonlyfifteeneachhour.Buteverythirty-threeyearsartobjectpassesthroughoursolarsystem(太阳系)thatchangestheLeonidmeteorshower.
Acomet(彗星)isalargebodyofgasiceandrock.Cometsleavebehindthesematerialsastheyorbitthesun.EachyeararoundNovember18ththeEarthpassesthroughmaterialleftbehindbyacometcalledTempel-Tuttle.
IntheFebruaryof1998cometTempel-Tuttlereturnedtotheinnersolarsystem.Astronomers(天文学家)havefoundthattheLeonidmeteorshowercanbecomeveryactiveforaboutfiveyearsaftertheappearanceofthatcomet.
AstronomersalsohavediscoveredthateachappearanceofcometTempel-Tuttleleavesbehindadifferentpathofmaterial.ThisdiscoveryhaspermittedastronomerstoknowwhentheLeonidmeteorshowermaybemostintense.SomeastronomersbelievetheLeonidsthismonthmaybeameteorstorm.
In1833observersintheeasternUnitedStatessawanintensemeteorstorm.Onepersonestimatedthatmeteorsfellatarateoften-thousandanhouraboveWestPointNewYork.In1966peopleinthewesternUnitedStatessawanotherintenseLeonidmeteorstorm.
ThisyearastronomersbelievethattherewillhetwoperiodsofheavymeteoractivitystartingonNovember18th.AtTenHoursUniversalTimeobserversinNorthAmericashouldseealargenumberofmeteors.
AnotherperiodofmeteoractivityshouldhappenataboutEighteenHoursUniversalTime.ObserversinEastAsiaandwesternAustraliawillseeitbest.AstronomerswhohaveresearchedtheLeonidssaythebestchancetoseeameteorstormmayhethisyearandnextyear.
1.Thispassagemainlytell
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