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高中英语Sailingtheoceans-Reading课件新人教版教材选修9课件.ppt

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ReadingThefourbasicinstrumentsfornavigation:Sinan,InchAstrolabe,Sextantandnauticalmap.ItwasinventedbyZhangHengintheHandynasty.Itismadeupofabronzefoundation(青铜地盘)andmagneticspoon(磁勺)whichismadeofnaturalmagnet,positionedrightinthecentralofthefoundation.Thehandleofthespoonpointstothesouth,whiletheothersidepointstothenorth.WhentheSinanisinthestill,thehandleofthespoonpointstothesouthbecauseofinfluenceoftheterrestrialmagnetism(地磁).Ithas17starslistedaswell asamapoftheskyoverhead (for37degrees)andthe ecliptic(黄道).Thetimeof dayornightisontheoutside edgewithnoonatthetopoftheAstrolabeandmidnightatthebottom.Itcomeswithacarryingchain,apouch,andabookonitsuse.Thereversesidehasasightformeasuringtheelevationsoftheheavenlybodies.sextantThesextantisanavigationalinstrumentformeasuringtheanglebetweenthehorizonandsomeobjectinthesky.Firstasailorlooksatthehorizonthroughaneyepiece.Atthesametimehecanseelightfromthesunorastarreflectedoffasmallmirrorontopoftheinstrument,ontoasecondmirrorandintotheeyepiece.Thenavigatorcanthenseetwoimages,thehorizonandthesunsidebyside.Hecanthenmeasuretheanglebetweenthemonascaleatthebottomoftheinstrument.Thescalegoesfrom0to120degrees.Anearlierinstrument,calledaquadrant,measuredinangleinthesamewaybutitcouldonlymeasureanglesfrom0to90degrees.nauticalchartNauticalchartsaremapsofthedepthoftheseaandthecurrentsoftheoceans.Theyprovidemodernsailorswithroutesthroughtheseas,ratherlikeroadsthroughthecountryside.Theinformationbegantobecollectedinthenineteenthcenturyandhascontinuedtobeupdatedeversince.ThesechartswerenotavailabletoCaptainBlighorZhengHe.Discuss2.Whichdoyouthinkwaseasiertoworkout:latitudeorlongitude?3.Canyouidentifytheseearlynavigationalinstrumentsseamenusedandexplainhowtheyareused?4.Whichonesdoyouthinkarestillused today?1.Wheredothesematerialscomefrom? 2.Whatdidtheearlynavigatorusetohelpthemnavigate? 3.Whatnaturalobjectswereusedtoassistthenavigation? 4.Isiteasiertomeasurelongitudeorlatitude? 5.Dotheastrolabe,thequadrantandthesextantmeanthesamething?Comprehending