How many stars may have been included in Hipparchus’s star catalog?

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Engraving of six astronomers, with Hipparchus seated at center and, from left to right, Galileo, Johannes Hevelius, Tycho Brahe, Nicolaus Copernicus, and Ptolemy standing, each holding scientific instruments. — Hipparchus “Six astronomers,” the frontispiece of *Astronomica Institutio* (1692) by Jan Luyts, engraving after drawing by Gerard Hoet. Hipparchus is seated at center with from left to right: Galileo, Johannes Hevelius, Tycho Brahe, Nicolaus Copernicus, and Ptolemy.

The exact number of stars included in the star catalog created by Hipparchus is not definitively known, as only fragments of his original work have survived. While some historical sources suggest he completed a catalog in 129 BCE containing approximately 850 stars, other scholars note that the precise count remains a subject of historical uncertainty.12

Much of the debate surrounding the size of his catalog stems from the Almagest, in which Ptolemy presents a list of 1,022 stars. Many historians argue that Ptolemy’s catalog was largely derived from the work of Hipparchus, adjusted for the effects of precessional motion, though this remains a controversial topic in the study of ancient astronomy.1