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1、Armillary_SphereHumboldtStateUniversity→DepartmentofChemistryRichardA.PaselkTheArmillarySphereAnarmillarysphereisbasicallyaskeletalcelestialspherewithamodeloftheEarthor,later,oftheSunplacedinthecenter.Itisusefulasateachingtoolandasananalogcomputerforsolvingvariousastronomicalproble
2、mstoacrudedegreeofaccuracy.ArmillaryspheresweredevelopedbytheGreeksinantiquityforuseasteachingtools.Inlargerandmorepreciseformstheywerealsousedasobservationalinstruments,beingpreferredbyPtolemy.Armillaryspheresbecamepopularagaininthelatemiddleages.WiththeadventoftheCopernicanmodelo
3、faSuncenteredUniversepairsofspherescontrastingtheCopernicanandPtolomaicmodelsbecamecommonteaching/demonstrationtools.Suchsmallteachingsphereremainedpopularthroughthenineteenthcentury.AnexcellentdiscussionofcelestialandarmillaryspheresisfoundinChapter2ofEvans.TheArmillarysphereconsi
4、stsoftwomajorcomponents,thesphereandthestand,asseeninthefigureabove.TheheartoftheArmillarysphereisthesphereitself,whichwasoftenmadeandusedalone.Renaissancepaintersfrequentlyshowspheresonhandlesinpaintingsofscholarsetc.ThecentralbodyinthesphererepresentstheEarth,whichwas,ofcourse,co
5、nsideredthecenteroftheUniverse.The106/25/200815:05Armillary_SpherecoluresandtheEquator(theringsdefiningthesphere)representthefirmament,thatis,thesphereuponwhichthefixedstarsreside.Thebandgoingaroundthesphere,atanangletotheequator,representsthezodiac.Thelinerunningthroughthemiddleof
6、thisbanddefinestheecliptic,orthepathfollowedbytheSunthroughthesky.Thewidthofthebandisideallyabout±9°toincludethewanderingoftheMoonandplanetsaboveandbelowtheSun'spath.ThevariousconstellationsoftheZodiacalsofallalongthisband.TheSphereInthediscussionbelowthenumbersrefertothepartsinthe
7、numberedview:206/25/200815:05Armillary_SphereMaterials:Thesphereitselfisdefinedbythreerings:thetheEquinoctialColure(9),theSolstitialColure(10),andtheEquator(5).Theseringswerefabricatedfromheavy(8G;1/8")brasssheetcutinto1/4'widestrips.ThebroadbandoftheEcliptic(6)wasfabricatedfromath
8、in(20G)brasssheetcuttogive
