ThePlanisphaerium is a work byPtolemy. The title can be translated as "celestial plane" or "star chart". In this work Ptolemy explored the mathematics of mapping figures inscribed in thecelestial sphere onto aplane by what is now known asstereographic projection. This method of projection preserves the properties of circles.
Originally written inAncient Greek,Planisphaerium was one of many scientific works which survived from antiquity inArabic translation. One reason whyPlanisphaerium attracted interest was that stereographic projection was the mathematical basis of theplane astrolabe, an instrument which was widely used in the medieval Islamic world. TheSuda lists a work of Ptolemy titledSimplification of the Sphere (Ancient Greek:Ἅπλωσις ἐπιφανείας σφαίρας) which is presumed to bePlanisphaerium. In 1143 the work was translated from Arabic into Latin byHerman of Carinthia, who also translated commentaries byMaslamah Ibn Ahmad al-Majriti.[1] The oldest known translation is in Arabic done by an unknown scholar as part of theTranslation Movement inBaghdad.[2]
The word planisphere (Latin planisphaerium) was originally used in the second century by Ptolemy to describe the representation of a spherical Earth by a map drawn in the plane.[3]
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