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1、Unit2SailingtheoceansWarmingup、pre-reading、reading&comprehendingWarmingup:Learnaboutthefourbasicinstrumentsfornavigation:Sinan,InchAstrolabe,Sextantandnauticalmap.Sinan,theancientChinesecompass.ItwasinventedbyZhangHengintheHandynasty.Itismadeupofabronzefoundati
2、on(青铜地盘)andmagneticspoon(磁勺)whichismadeofnaturalmagnet,positionedrightinthecentralofthefoundation.Thehandleofthespoonpointstothesouth,whiletheothersidepointstothenorth.WhentheSinanisinthestill,thehandleofthespoonpointstothesouthbecauseofinfluenceoftheterrestria
3、lmagnetism(地磁).Ithas17starslistedaswellasamapoftheskyoverhead(for37degrees)andtheecliptic.ThetimeofdayornightisontheoutsideedgewithnoonatthetopoftheAstrolabeandmidnightatthebottom.Itcomeswithacarryingchain,apouch,andabookonitsuse.Thereversesidehasasightformeasu
4、ringtheelevationsoftheheavenlybodies.astrolabesextantThesextantisanavigationalinstrumentformeasuringtheanglebetweenthehorizonandsomeobjectinthesky.Firstasailorlooksatthehorizonthroughaneyepiece.Atthesametimehecanseelightfromthesunorastarreflectedoffasmallmirror
5、ontopoftheinstrument,ontoasecondmirrorandintotheeyepiece.Thenavigatorcanthenseetwoimages,thehorizonandthesunsidebyside.Hecanthenmeasuretheanglebetweenthemonascaleatthebottomoftheinstrument.Thescalegoesfrom0to120degrees.Anearlierinstrument,calledaquadrant,measur
6、edinangleinthesamewaybutitcouldonlymeasureanglesfrom0to90degrees.nauticalchartNauticalchartsaremapsofthedepthoftheseaandthecurrentsoftheoceans.Theyprovidemodernsailorswithroutesthroughtheseas,ratherlikeroadsthroughthecountryside.Theinformationbegantobecollected
7、inthenineteenthcenturyandhascontinuedtobeupdatedeversince.ThesechartswerenotavailabletoCaptainBlighorZhengHe.Pre-reading1.Howdoyouthinkseamenfoundtheirwaybeforemodernaccuratemethodsofnavigationwereinvented?Keptclosetotheshore,usednaturesuchasthesun,wind,birds,t
8、ide,etc,tohelpthem,andusedsomeoftheinstrumentsincludingacompass,astrolabe,etc.2.Whichdoyouthinkwaseasiertoworkout:latitudeorlongitude?Latitude,becauseitwasusedtomeasurehowfa
