ca. AD 150: Ptolemy (ca. AD 90-160) was the author of several scientific treatises. The most important one is the Almagest ("The Great Treatise"), consisting of 13 books. There he had gathered the astronomical knowledge of his predecessors scattered throughout 800 years. The books VII and VIII contain a star catalogue of 1022 stars, which is an appropriated and supplemented version of Hipparchus' list. Ptolemy's astronomical models were accompanied by convenient tables, which could be used to compute the future or past positions of the planets. He also described the construction of a celestial globe (Book V, Ch. I). It consisted of a graduated circle inside which another could slide. As much as we know, Ptolemy built at least one by himself.

Ptolemy's contribution to the history lies in the immense influence of the Almagest on the scientific ideology throughout the Middle Ages. Since many other works have been lost, historians use his book as the source for information on ancient Greek astronomy in general. Some claim that Ptolemy was mathematician of the very top rank, others argue that his improvements to science were rather low. Fact is that we know very little of Ptolemy's life and circumstances of investigation. It is quite sure that he made some celestial observations of his own in Alexandria and compared them with previous ones, mainly by Hipparchus.