Hipparchus
190 BC – 120 BC
Greek
Ancient World
First star catalog and stellar magnitude system
Biography
The Farnese Atlas (2nd century AD) — oldest surviving depiction of the celestial sphere. The constellations are believed to derive from Hipparchus's lost star catalog.
National Archaeological Museum, Naples. Photo: Carlo Raso. Public domain, via Wikimedia Commons
Hipparchus of Nicaea is widely regarded as the greatest astronomer of antiquity. Working from the island of Rhodes, he made meticulous observations that set the standard for astronomical precision for centuries to come. He is credited with the invention of trigonometry and was the first to compile a systematic star catalog, listing approximately 850 stars with their positions and brightness. His most remarkable discovery was the precession of the equinoxes — a slow shift in the orientation of Earth's axis — which he detected by comparing his own observations with those made 150 years earlier. Hipparchus also developed improved methods for predicting solar and lunar eclipses and calculated the distance to the Moon with impressive accuracy.
Key Discoveries
Created the first comprehensive star catalog with ~850 stars classified by brightness.
Invented the stellar magnitude system (1 = brightest, 6 = faintest) still used in modified form today.
Discovered the precession of the equinoxes.
Developed trigonometric methods for astronomical calculations.
Calculated the Moon's distance from Earth to within 7% of the modern value.