Ptolemy

Claudius Ptolemy was a mathematician, astronomer, and geographer who lived in Alexandria, Egypt during the Roman period. His monumental work, the Almagest, synthesized centuries of Greek astronomical knowledge into a comprehensive mathematical model of the cosmos. The Ptolemaic geocentric system, with its ingenious use of epicycles and deferents, could predict planetary positions with remarkable accuracy and remained the dominant astronomical model until Copernicus. Beyond the Almagest, Ptolemy wrote the Tetrabiblos on astrology, the Geography which mapped the known world, and the Optics on visual perception. His star catalog, based partly on Hipparchus's work, listed 1,022 stars in 48 constellations — a framework that influenced constellation boundaries to this day.

Compiled the Almagest, the most influential astronomical text for over a millennium. Cataloged 1,022 stars in 48 constellations. Developed the Ptolemaic geocentric model with epicycles to predict planetary motions. Established mathematical methods for calculating eclipses, planetary conjunctions, and star positions.