Ptolemy was a Greek astronomer and the author of works on physics, mathematics, optics and geography. He produced the data for creating a world map in about 150 AD.
One of the most influential Greek astronomers and geographers of his time, Ptolemy propounded the geocentric theory in a form that prevailed for 1400 years.
We know very little of Ptolemy's life. He made astronomical observations from Alexandria in Egypt during the years AD 127-41. Ptolemy was born in Alexandria in Egypt.
His name, Claudius Ptolemy, is of course a mixture of the Greek Egyptian 'Ptolemy' and the Roman 'Claudius'. This would indicate that he was descended from a Greek family living in Egypt and that he was a citizen of Rome.
The Almagest is the earliest of Ptolemy's works and gives in detail the mathematical theory of the motions of the Sun, Moon, and planets. Ptolemy made his most original contribution by presenting details for the motions of each of the planets.Ptolemy used geometric models to predict the positions of the sun, moon, and planets, using combinations of circular motion known as epicycles. Ptolemy devised new geometrical proofs and theorems. He obtained, using chords of a circle and an the approximation pie= 3 17/120 = 3.14166. Ptolemy also wrote a work on astrology.