Claudius Ptolemy

Claudius Ptolemy was a Greek-Egyptian mathematician, astronomer, geographer, and astrologer who lived in the city of Alexandria during the height of the Roman Empire. His treatises in astronomy, geography, optics, and music theory dominated European and Islamic scholarship for more than a thousand years.

Few biographical details survive. He was probably born around 100 AD, most likely in Egypt, and was a Roman citizen of Greek cultural background, as his name Claudius indicates a family granted citizenship under the Julio-Claudian emperors. He wrote in Greek and is associated entirely with Alexandria, where he made astronomical observations recorded between roughly 127 and 141 AD.

His Mathēmatikē Syntaxis, known in its Arabic-derived title as the Almagest, presents a geometrical model of the heavens with a stationary Earth at the centre, using epicycles and equants to predict planetary motion with substantial accuracy. The work catalogues 1,022 stars in 48 constellations and remained the basis of mathematical astronomy until the publication of Copernicus's De revolutionibus in 1543.

He also produced the Geographia, a manual of map-making with coordinates for some 8,000 places; the Tetrabiblos, on astrology; the Optics; the Harmonics, on music theory; and the planetary Handy Tables. He is thought to have died in Alexandria around 170 AD, aged about 70.

His name Claudius derives from a Roman family name based on Latin claudus meaning "lame." Claudius has been borne by Roman emperors and Christian saints and remains in occasional use in many European languages.