Precession of the equinoxes
Precesión de los equinoccios
- Date
- c. 130 BCE · confidence medium
- Place
- Rhodes, Greece
- Credited to
- Hipparchus of Nicaea
- People
- 👤 Hiparco de Nicea190 BCE–120 BCE
- Field
- Cosmos & Earth
What was discovered
By comparing his measurements of Spica with those of Timocharis 150 years earlier, Hipparchus discovered that the equinoctial point slowly shifts (about 1° per century). It is the first detection of a long-term change in the sky.
Some historians argue that the Babylonians knew of the phenomenon, without conclusive evidence.
What it led to
- Distinction between tropical and sidereal year
- Precise calendars (Julian, Gregorian)
- Newtonian explanation via the Earth's oblateness
Built on
Made possible
- Ptolemaic geocentric model (Almagest)c. 150
- Star catalogues with a reference epoch