关于经纬度的英文原文及翻译.docx

关于经纬度的英文原文及翻译.docx

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关于经纬度的英文原文及翻译

LatitudeandLongitude

AnylocationonEarthisdescribedbytwonumbers--its latitude andits longitude.Ifapilotoraship'scaptainwantstospecifypositiononamap,thesearethe"coordinates"theywoulduse.

Actually,thesearetwo angles,measuredindegrees,"minutesofarc"and"secondsofarc."Thesearedenotedbythesymbols（ °, ', " ）e.g.35°43'9"meansanangleof35degrees,43minutesand9seconds（donotconfusethiswiththenotation（',"）forfeetandinches!

）.Adegreecontains60minutesofarcandaminutecontains60secondsofarc--andyoumayomitthewords"ofarc"wherethecontextmakesitabsolutelyclearthattheseare not unitsoftime.

 CalculationsoftenrepresentanglesbysmalllettersoftheGreekalphabet,andthatwaylatitudewillberepresentedbyλ（lambda,GreekL）,andlongitudebyφ（phi,GreekF）.Hereishowtheyaredefined. 

PLEASENOTE:

 Chartsusedinoceannavigationoftenusethe OPPOSITE notation--λforLONGITUDEandφforLATITUDE.Theconventionfollowedhereresemblestheoneusedbymathematiciansin3dimensionsfor sphericalpolarcoordinates.

  ImaginetheEarthwasa transparentsphere（actuallytheshapeisslightlyoval;becauseoftheEarth'srotation,itsequatorbulgesoutalittle）.ThroughthetransparentEarth（drawing）wecanseeitsequatorialplane,anditsmiddlethepointisO,thecenteroftheEarth.

TospecifythelatitudeofsomepointPonthesurface,drawtheradiusOPtothatpoint.Thenthe elevationangle ofthatpoint abovetheequator isitslatitudeλ--northernlatitudeifnorthoftheequator,southern（ornegative）latitudeifsouthofit.

Latitude

Ingeography,latitude（φ）isageographiccoordinatethatspecifiesthenorth–southpositionofapointontheEarth'ssurface.Latitudeisanangle（definedbelow）whichrangesfrom0°attheEquatorto90°（NorthorSouth）atthepoles.Linesofconstantlatitude,orparallels,runeast–westascirclesparalleltotheequator.LatitudeisusedtogetherwithlongitudetospecifythepreciselocationoffeaturesonthesurfaceoftheEarth.Twolevelsofabstractionareemployedinthedefinitionofthesecoordinates.Inthefirststepthephysicalsurfaceismodelledbythegeoid,asurfacewhichapproximatesthemeansealevelovertheoceansanditscontinuationunderthelandmasses.Thesecondstepistoapproximatethegeoidbyamathematicallysimplerreferencesurface.Thesimplestchoiceforthereferencesurfaceisasphere,butthegeoidismoreaccuratelymodelledbyanellipsoid.Thedefinitionsoflatitudeandlongitudeonsuchreferencesurfacesaredetailedinthefollowingsections.Linesofconstantlatitudeandlongitudetogetherconstituteagraticuleonthereferencesurface.Thelatitudeofapointontheactualsurfaceisthatofthecorrespondingpointonthereferencesurface,thecorrespondencebeingalongthenormaltothereferencesurfacewhichpassesthroughthepointonthephysicalsurface.LatitudeandlongitudetogetherwithsomespecificationofheightconstituteageographiccoordinatesystemasdefinedinthespecificationoftheISO19111standard.

Sincetherearemanydifferentreferenceellipsoidsthelatitudeofafeatureonthesurfaceisnotunique:

thisisstressedintheISOstandardwhichstatesthat"withoutthefullspecificationofthecoordinatereferencesystem,coordinates（thatislatitudeandlongitude）areambiguousatbestandmeaninglessatworst".Thisisofgreatimportanceinaccurateapplications,suchasGPS,butincommonusage,wherehighaccuracyisnotrequired,thereferenceellipsoidisnotusuallystated.

InEnglishtextsthelatitudeangle,definedbelow,isusuallydenotedbytheGreeklower-caseletterphi（φorɸ）.Itismeasuredindegrees,minutesandsecondsordecimaldegrees,northorsouthoftheequator.

MeasurementoflatituderequiresanunderstandingofthegravitationalfieldoftheEarth,eitherforsettinguptheodolitesorfordeterminationofGPSsatelliteorbits.ThestudyofthefigureoftheEarthtogetherwithitsgravitationalfieldisthescienceofgeodesy.Thesetopicsarenotdiscussedinthisarticle.（SeeforexamplethetextbooksbyTorgeandHofmann-WellenhofandMoritz.）

ThisarticlerelatestocoordinatesystemsfortheEarth:

itmaybeextendedtocovertheMoon,planetsandothercelestialobjectsbyasimplechangeofnomenclature.

ImaginetheEarthwasa transparentsphere（actuallytheshapeisslightlyoval;becauseoftheEarth'srotation,itsequatorbulgesoutalittle）.ThroughthetransparentEarth（drawing）wecanseeitsequatorialplane,anditsmiddlethepointisO,thecenteroftheEarth.

TospecifythelatitudeofsomepointPonthesurface,drawtheradiusOPtothatpoint.Thentheelevationangleofthatpointabovetheequatorisitslatitudeλ--northernlatitudeifnorthoftheequator,southern（ornegative）latitudeifsouthofit.

[Howcanonedefinetheanglebetweenalineandaplane,youmaywellask?

Afterall,anglesareusuallymeasuredbetweentwolines!

Goodquestion.Wemustusetheanglewhichcompletesitto90degrees,theonebetweenthegivenlineandoneperpendiculartotheplane.Herethatwouldbetheangle（90°-λ）betweenOPandtheEarth'saxis,knownastheco-latitudeofP.]

OnaglobeoftheEarth,linesoflatitudearecirclesofdifferentsize.Thelongestisthe equator,whoselatitudeiszero,whileatthepoles--atlatitudes90°northand90°south（or-90°）thecirclesshrinktoapoint.

Longitude

Longitudeisageographiccoordinatethatspecifiestheeast-westpositionofapointontheEarth'ssurface.Itisanangularmeasurement,usuallyexpressedindegreesanddenotedbytheGreekletterlambda（λ）.Meridians（linesrunningfromtheNorthPoletotheSouthPole）connectpointswiththesamelongitude.Byconvention,oneofthese,thePrimeMeridian,whichpassesthroughtheRoyalObservatory,Greenwich,England,wasallocatedthepositionofzerodegreeslongitude.ThelongitudeofotherplacesismeasuredastheangleeastorwestfromthePrimeMeridian,rangingfrom0°atthePrimeMeridianto+180°eastwardand−180°westward.Specifically,itistheanglebetweenaplanecontainingthePrimeMeridianandaplanecontainingtheNorthPole,SouthPoleandthelocationinquestion.（Thisformsaright-handedcoordinatesystemwiththezaxis（righthandthumb）pointingfromtheEarth'scentertowardtheNorthPoleandthexaxis（righthandindexfinger）extendingfromEarth'scenterthroughtheequatoratthePrimeMeridian.）

Alocation'snorth–southpositionalongameridianisgivenbyitslatitude,whichisapproximatelytheanglebetweenthelocalverticalandtheplaneoftheEquator.

IftheEarthwereperfectlysphericalandhomogeneous,thenthelongitudeatapointwouldbeequaltotheanglebetweenaverticalnorth–southplanethroughthatpointandtheplaneoftheGreenwichmeridian.EverywhereonEarththeverticalnorth–southplanewouldcontaintheEarth'saxis.ButtheEarthisnothomogeneous,andhasmountains—whichhavegravityandsocanshifttheverticalplaneawayfromtheEarth'saxis.Theverticalnorth–southplanestillintersectstheplaneoftheGreenwichmeridianatsomeangle;thatangleistheastronomicallongitude,calculatedfromstarobservations.ThelongitudeshownonmapsandGPSdevicesistheanglebetweentheGreenwichplaneandanot-quite-verticalplanethroughthepoint;thenot-quite-verticalplaneisperpendiculartothesurfaceofthespheroidchosentoapproximatetheEarth'ssea-levelsurface,ratherthanperpendiculartothesea-levelsurfaceitself.

Ontheglobe,linesofconstantlongitude（"meridians"）extend frompoletopole,likethesegmentboundariesonapeeledorange.

  Everymeridianmustcrosstheequator.Sincetheequatorisa

circle,wecandivideit--likeanycircle--into360degrees,andthe longitudeφofapoint isthenthemarkedvalueofthat

divisionwhereitsmeridianmeetstheequator.

Whatthatvalueisdependsofcourseonwherewebegintocount--onwhere zerolongitude is.Forhistoricalreasons,themeridianpassingtheoldRoyalAstronomicalObservatoryinGreenwich,England,istheonechosenaszerolongitude.LocatedattheeasternedgeofLondon,theBritishcapital,theobservatoryisnowapublicmuseumandabrassbandstretchingacrossitsyardmarksthe"primemeridian."Touristsoftengetphotographedastheystraddleit--onefootintheeasternhemisphereoftheEarth,theotherinthewesternhemisphere.

Alinesoflongitudeisalsocalledameridian,derivedfromtheLatin,frommeri,avariationof"medius"whichdenotes"middle",anddiem,meaning"day."Thewordoncemeant"noon",andtimesofthedaybeforenoonwereknownas"antemeridian",whiletimesafteritwere"postmeridian."Today'sabbreviationsa.m.andp.m.comefromtheseterms,andtheSunatnoonwassaidtobe"passingmeridian".Allpointsonthesamelineoflongitudeexperiencednoon（andanyotherhour）atthesametimeandwerethereforesaidtobeonthesame"meridianline",whichbecame"meridian"forshort.

Abouttime--LocalandUniversal

  Twoimportantconcepts,relatedtolatitudeand（especially）longitudeare Localtime（LT） and Universaltime（UT）

Localtime isactuallyameasureofthepositionoftheSunrelativetoalocality.At12noonlocaltimetheSunpassestothesouthandisfurthestfromthehorizon（northernhemisphere）.Somewherearound6amitrises,andaround6pmitsets.LocaltimeiswhatyouandIusetoregulateourliveslocally,ourworktimes,mealsandsleep-times.

Butsupposewewantedtotimeanastronomicalevent--e.g.thetimewhenthe1987supernovawasfirstdetected.Forthatweneedasingleagreed-onclock,markingtim