一篇关于天文学的英语短文

TheGreekHeavenlyThoughts

TheGreekwasthefirstrecognizethedistinctionbetweenthenaturalandthesupernatural.Inotherwords,theyfoundthenature,sincethen,thecosmology(宇宙学)couldneverbemaintainasystemofmyth.

Gradually,theGreekbelievedthemselvestoliveinacosmos,andconsideredthecosmostobeanentirelynaturalplace.Besidestheysawanorderinthecosmos.Theorder,tothem,notonlymeansanarrange,butalsoagoodorder,andalsoabeautiful,elegantorder.Withanoptimism(乐观主义),theybelievedtheorder,andthecosmoswerecomprehensible(可知的),andfurthermore,couldbedescribedinwordsandnumbers.WhentheGreekformedthesecrucialideas,someearliestphilosophersandscientistswereimportantandinfluential.TheMilesians(米利都学派得的哲学家),includingThales(泰勒斯),Anaximander(阿纳克西曼德),describedthecosmosinentirelynaturaltermsforthefirsttime.Heraclitus(赫拉克立特)insistedthatthecosmosworkedaccordingtoalogos(理性),whichmean“word”,“account”,“measure”,and“proportion”,andifwegraspthislogos,thecosmoscouldbeunderstoodanddescribedwell.

AftertheGreekacceptedtheideathatthecosmoswasanaturalplaceandcomprehensible,somepre-Socratics(前苏格拉底时代德哲学家)overcamesomesignificantconceptual(观念上的)hurdlestoachieveamoresophisticatedcosmology.Therewasthemovefromahemispherical(半球形)universetoaspherical(球形)one,andaearthsupportedbywatertosupportedbyair,andthentoonewhichneednosupport.IntheearlierGreekcosmologies,objectswerethoughttodropinparallelstraightlinesfromthetopofthecosmostothebottom,thisledtotheproblemwhytheearthdoesn’tfalltothebottomofthecosmos,sointhissortofthecosmos,somethingisrequiredtosupporttheearth.ThenAristotleplacedtheearthatthecenterofthecosmos,therewasnotheproblemoftheearthdropping.Hebelievedthatobjectsmovedtothecenterofthecosmos,thatistheearthitself.

TheideathattheearthwascentralandstabledominatedGreekastronomyandcosmology.InGreekminds,itcanexplainmanyphenomena.Firstly,theexperiencetoldGreek,ifonewasinrapidmotion,hecertainlyknewaboutit,sotheythought,iftheearthhasadailyrotationfromwesttoeast,thereshouldbeconstantwindfromeasttowest;iftheearthisinmotionaroundthesun,allobjectswillsweepoffthefaceoftheearth.Secondly,becausetheyhadnoknowledgeofgravity,theybelieveiftheearthinrapidmotion,itwilldisintegrate(解体).Thirdly,iftheearthtakesupdifferentpositionsrelativetothestars(恒星),thereshouldbeastellarparallax(恒星视差量),onecandetectslightchangesintheapparentpositionsofthestarsfromtheearth.

WhentheGreekphysics,astronomy,philosophyandcommonsenseallseemedtoindicateanimmobileearth,therewasanimportantconsequence,allofthemotionsoftheheavenswererealmotionstotheearth,notapparentonesduetothemotionoftheearth.

Attheoutset,Greekobservationalastronomywasratherdivorced(背离)fromphilosophicalspeculationaboutthenatureofthecosmos.Someobservedtheheavensandtookcarefulnotesofwhattheysaw,someproducedcosmologicalmodelsbasedongeneralphilosophicalconsiderations.Butnoonegaveacosmologicalmodelthatwereanywherenearexplaining,inaprecisemanner,thephenomenathathadbeenrecord.ThePythagoreans(毕达哥拉斯学派的哲学家)madethefirstattempt.Theybelievedinthecenterofthecosmoswasafire,notthesun,thefirewasshieldfromtheearthbyabodyknownasthecounterearth.Themodelwasvagueandspeculative,andtheearthmovesaroundthefire,andbetweenthefireandearth,therewasthecounterearth.Plato(柏拉图)producedaslightlybettermodel,hadcentralearth,withthesun,themoon,thefiveplanetsandthestarsorbitingaroundit.ThenitwasabasicassumptionofGreekastronomyandcosmology,ifsomemotionsseemsnotcircularorregular,almostallGreekphilosophersandscientistswouldconsidertheseassomecombinationofseveralcircularandregularmotions.Neitheroftwomodelscouldaccountfortwoimportantphenomenarelatingtothepointatwhichthesunsets.Thesundoesnotalwayssetduewest(正西方).Wherethesunsetsduringayearchangesfromamaximumof23.5ºnorthofwesttoamaximumof23.5°northofwest.Solstices(至日，包括冬至、夏至)occuratthemaximumpoints,whileequinoxes(分日，包括春分、秋分)occurattheduewest.LaterPlatogavethefirstmodelthatcouldgiveareasonableaccountforthesephenomena.ThemodelwasoneofthemostimportantGreekcosmologicalmodels.Platomadethefirstseriousattempttouniteastronomicalphenomenaandcosmologicaltraditions.Heinsistedthatthesun,themoon,haveacombinationoftworegularcircularmotions,that’stosay,thesunandthemoonhaveasecondmotioninadditionthedailyone,offset(偏移)atanangletoit.Astothefiveplanets,whicharewanderingintheheavenapparently,Platogaveasimilarbutmorecomplexexplanation.Themodelcouldgiveareasonableexplanationapproximately,butcouldn’texplaintheplanetsexceptivemotions.Theywillprogressagainstthebackgroundofthefixedstarsoverayearortwo,orevenlonger,thentheywillhaltsuddenly,andgointheotherdirectionforawhile,stopagain,afterthat,progressinthenormaldirection.Facingaseriesstrangeexceptionsandmotionsoftheplanets,Eudoxus(人名，难以翻译，重要的哲学家、科学家)thoughtregressively(回归，追本溯源).HewasapupilofPythagorean,andhadacloserelationshipwithPlato.Aboutplanets,Plato’smodelhadtworegularcircularmovementsforeachplanet,Eudoxusgavefourcircularmovementsforeachplanet.Inthismodel,thefirstsphere(环),generateadailymotion;thesecondgeneratethemotionalongtheecliptic(黄道),theothertwoproduceapatternlikethefigure8laidonitssides(行星出现在黄道正负8度范围内).Besides,Eudoxushadarecordofplanets’motion,andmadeagooduseofmathematics,socomparedwithPlato’smodel,hisismoresophisticated.

Eudoxus’modelwasexcellentmodelforalongtime,butthereweresomeinherentdifficulties.Becausethedistancebetweentheearthandeachoneoffiveplanetsthatwecanseewithnakedeyes,alwayschanges,itisnotdifficulttofindthatallplanets’sizearevaryingapparently.Eudoxuscan’tcopewiththephenomenon,inhismodel,thedistancesbetweentheearthandtheplanetsareconstant,thatmeansthesizeofplanetscan’tvary.Accountfortheseproblems,Ptolemy(托勒密)producedawholenewsystemwhichwastolastfornearly1500years.Thesystemwasbasedoncombinationofregularcircularmotionstoo.Hegaveupconcentric(同心圆)spheremodelinfavorofasystembasedonadevice,theepicycle(本轮，天文模型的一种).Theepicycleisacombinationoftworegularcircularmotions,butnotaroundthesamecenter.Thecenterofsmallercirclemovesaroundthelargercircle.Thetwocirclescanproducedmanycomplexpatterns,becausethesepatterns,Ptolemywasabletoexplainmostproblemsthatbesettheconcentricspheremodel,includingthevariationofapparentsize,thebrightness,thevelocity(速度)oftheplanets.Besidestheepicycle,Ptolemymadeanothersubtlechange,theearthisoffsetfromthecenterofthesun’sorbit.Sothemodelcanaccountforthatseasonshaveslightlydifferentlengths.Nowbeforethetelescopewasinventedandnewphenomenathatcan’tbefoundwithnakedeyesweredetected,themodelisthebestintheancienttimes.

AftertalkingaboutsomeimportantGreekcosmologicalmodels,wehavetomentionanexceptiveastronomer,Aristarchus(阿里斯塔克斯).Heisthefirstonewhohavearevolutionarythinkingthattheearthisorbitingaroundthesun.Butsadly,wedon’tknowhowandwhyhecanbeawarethiswithoutanyideaaboutgravityandthephenomenawhichonlycanbedetectedwithtelescope,onlyweknowheisafollowerofAristotle.