Hipparchus
A star catalogue, trigonometry, and the discovery that the sky itself shifts.
- When
- Known to
- ± 20 years
- Era
- Classical, Holocene
Working around 150 BCE, Hipparchus compiles a catalogue of some 850 stars with positions and a magnitude scale still in use, develops the first trigonometric table, and by comparing his measurements with Babylonian records discovers the precession of the equinoxes — a wobble of the Earth's axis completing a cycle in 26,000 years. Detecting it required trusting observations made centuries earlier by another civilisation.