Star catalog

Hellenistic world and Roman Empire

Approximately in the 3rd century BC, the Greek astronomersTimocharis of Alexandria and Aristillus created another star catalogue. Hipparchus (c. 190 – c. 120 BC) completed his star catalogue in 129 BC, the earliest known attempt to map the entire sky, which he compared to Timocharis' and discovered that the longitude of the stars had changed over time. This led him to determine the first value of the precession of the equinoxes. In the 2nd century, Ptolemy (c. 90 – c. 186 AD) of Roman Egypt published a star catalogue as part of his Almagest, which listed 1,022 stars visible from Alexandria. Ptolemy's catalogue was based almost entirely on an earlier one by Hipparchus. It remained the standard star catalogue in the Western and Arab worlds for over eight centuries. The Islamic astronomer al-Sufi updated it in 964, and the star positions were redetermined by Ulugh Beg in 1437, but it was not fully superseded until the appearance of the thousand-star catalogue of Tycho Brahe in 1598.