A large astronomical treatise by the Greek astronomer Ptolemy Claudius Ptolemaeus, who worked in Alexandria between about AD 127 and 151. The name is an Arabic corruption of a Greek title, The Greatest, though Ptolemy’s original title was The Mathematical Collection. It ranks among the most important works on astronomy ever written. It included a star catalogue and dealt with the motion of the Moon and planets. The rules set out for calculating the future positions of the planets, on the basis of an Earth-centred universe, were used for centuries.