Ptolemy

Ptolemy, known as Claudius Ptolemaeus in Greek, was a mathematician, astronomer, geographer, and astrologer. He lived in Egypt under Roman rule and was believed to had been born in the town of Ptolemais Hermiou in the Thebaid. He lived from AD 90- 168. He was the author of several scientific treatises, the first which was the astronomical treatise now known as the Almagest. The second is the Geography, which is a thorough discussion of the geographic knowledge of the Greco-Roman world. The third is the astrological treatise known sometimes in Greek as the Apotelesmatika more commonly in Greek as the Tetrabiblos. Ptolemy claimed to have derived his geometrical models from selected astronomical observations by his predecessors spanning more than 800 years, though astronomers have for centuries suspected that his models’ parameterse were adopted independently of observations. The astronomical model that Ptolemy presented was shown in convenient tables which were used to compute the future or past position of the planets. Ptolemy’s model was geocentric and was almost universally accepted until the appearance of simpler heliocentric models during the scientific revolution. He estimated the Sun was at an average distance of 1210 Earth radii while the radius of the sphere of the fixed stars was 20,000 times the radius of the Earth. He also presented a tool that was quite useful for astronomical calculations in his Handy Tables, which tabulated all the data needed to compute the positions of the Sun, Moon, and planets, the rising and the setting of the stars, and eclipses of the Sun and Moon. In the Phaseies (Risings of the Fixed Stars) Ptolemy gave a parapegma, a star calendar or almanac based on the hands and disappearances of stars over the course of the solar year.