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1、celestialnavigationCelestialnavigationfordummiesIntroductionTheprinciplesofcelestialnavigationaresimple.Thehardermathematicscomeindetailsofcalculations,andacomputerprogramlikeASNAvwilltakecareofthisforyou,sodon'tbeafraidtoreadthispage.It'spleasanttounderstandhowitispos
2、sibletofindhispositiononEarthjustbelookingatafewstars…Thecelestialmechanicsisprecisionmechanics.Itispossibletocalculatetheexactpositionofaheavenlybody(star,planet,moon,sun)intheskyatanygiventime.Knowingthepositionhttp://www.seamanship.co.uk/deck/navigator/ASNAv/ASNAv%2
3、0Site/Text/celnav1.htm(1of4)5/4/20054:59:39PMcelestialnavigationofthestarinthesky,themeasureoftheanglebetweenthehorizonoftheobserverandthestar,usingasextant,isenoughtodeterminetheobserverpositioninlatitudeandlongitude(infact,wewillseethatatleasttwomeasuresareneeded).Le
4、t'sshowthisbytheexampleofanothersituationatsea:imagineyouobservealighthousefromacertaindistance.Withthesextant,youmeasuretheanglealphacorrespondingtotheheightofthelighthouseseenfromyourposition.Ifyouknowtheheighth,youcanfindyourdistancedfromthelighthouse.Onachart,youca
5、ndrawacirclecentredonthelighthousewitharadiusd.Youaresomewhereonthecircle.Thisisyourcircleofposition.Asecondobservationgivesyouasecondcircleofposition.Youareattheintersectionofthecirclesofposition.Infact,thereismostoften2intersectionsbutyourestimatedpositionorathirdobs
6、ervationwillhelpyoutochoosetherightone.Ifyoudon'tobservealighthousebuttheanglebetweenyourhorizonandastar,youaredoingcelestialnavigation.That'sit!http://www.seamanship.co.uk/deck/navigator/ASNAv/ASNAv%20Site/Text/celnav1.htm(2of4)5/4/20054:59:39PMcelestialnavigationOfco
7、urse,atthisstageweneedtolookalittlebitcloseratthecelestialmechanicstounderstandhowwecancalculatetheexactpositionofaheavenlybody(star,planet,moon,sun)inyourlocalskyatanygiventimeandwhichmathematicalrelationislinkingthealtitudeofabodytoacircleofposition.Unfortunately,iti
8、snotassimpleastan(alpha)=h/d.Celestialmechanics-ablueprintImaginetheEarthinspacesurroundedbyacelestialsphereonwhichal
