Hipparchus Catalogs Stars and Discovers Precession

Hipparchus of Nicaea completed the first comprehensive star catalog in 129 BCE, documenting positions and brightnesses of approximately 850 stars. Comparing his observations with earlier records from Timocharis and Aristillus, he noticed shifts in stellar positions. This led to his discovery of precession of the equinoxes—the gradual change in Earth's rotational axis orientation causing apparent stellar positions to shift over centuries. Hipparchus calculated precession at approximately 1° per century, close to the modern value of 1.38° per century. His catalog introduced the magnitude system for classifying stellar brightness, still used today with modifications.