Hipparchus is celebrated for several key contributions to astronomy. One of his most notable achievements was the discovery of the precession of the equinoxes. He noticed that the positions of the equinoxes were shifting over time, an observation that would later be pivotal in understanding Earth's axial precession. Additionally, Hipparchus compiled the first comprehensive star catalog of the western world, listing about 850 stars. He also devised a system of stellar magnitudes to classify stars based on their brightness, a system that, although refined, is still in use today. Moreover, Hipparchus made significant strides in mathematical astronomy, particularly with his work on trigonometry. He developed the first known trigonometric table, which allowed for more precise calculations of celestial phenomena.
