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Ptolemy (c.100–168)





Ptolemy
Egyptian astronomer, mathematician, and geographer, also known as Claudius Ptolemaeus, who worked at the great library in Alexandria and based his astronomy on the belief that all heavenly bodies revolve around Earth (see Ptolemaic system). He authored a 13-volume work called Mathematical Syntaxis, better known by its later Arabic name, the Almagest, which is a compendium of the astronomical works of Hipparchus, Aristotle, and others, and represents the most complete description of the Universe as it was then understood. The Almagest includes a star catalogue containing 48 constellations, using the names we still use today. Although no longer in serious use, the catalogue lists 1,022 stars visible from Alexandria and was used as a standard in the Western and Arab worlds for over a thousand years. An even earlier star catalogue was that of Timocharis of Alexandria, written in about 300 BC. and later used by Hipparchus. Ptolemy's work promulgated a sophisticated version of the Aristotelian, geocentric theory which held sway in the west until the Copernican Revolution.


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   • ASTRONOMERS AND ASTROPHYSICISTS
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