What model of the universe did Hipparchus use?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

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.

Hipparchus utilized a geocentric cosmology, which assumed a spherical, stationary Earth at the centre of the universe. Within this framework, he modeled the motions of the Sun and Moon using the eccenter and epicyclic models.21

These models were based on the principle of compounding uniform circular motions to account for observed irregularities in celestial movement. Hipparchus demonstrated that the eccentric circle—a circle where Earth is positioned away from the geometric centre—was mathematically equivalent to an epicycle-deferent system. While he successfully applied these tools to the Sun and Moon, he did not attempt to devise a comprehensive planetary theory, as he recognized that the movements of the planets were significantly more complex.231