Hipparchus of Nicaea (c.190–120 BC), an astronomer who worked mainly on Rhodes, compiles between c.160 and c.127 BC the first quantitative star catalogue in Western history, with positions and magnitudes of about 850 stars. He discovers the precession of the equinoxes by comparing his observations with those of Timocharis a century earlier, detecting a shift of about 2° in 150 years. He introduces the system of stellar magnitudes (1 to 6) still used today with modifications. He develops trigonometry as a systematic tool for astronomy, with the first documented table of chords. Hipparchus establishes the empirical-quantitative method of astronomy: systematic observation, cataloguing, prediction. Al-Battani corrects and extends his work eight centuries later; Copernicus cites him directly in De Revolutionibus.