Hipparchus discovers Precession of the equinoxes
127 BC discovered
After measuring and comparing the different lengths of the tropical year (the time it takes the Sun to return to an equinox) versus the sidereal year (the time it takes the Sun to return to a fixed star), he deduced that the equinoxes precessat a rate of not less than 1° per century.
He wrote two books on precession, On the Displacement of the Solsticial and Equinoctial Points and On the Length of the Year. Ptolemy cites both in his Almagest.
Note:
- tropical year → the time it takes the Sun to return to an equinox
- sidereal year → the time it takes the Sun to return to a fixed star
Subjects Who or What discovered?
-
Hipparchus (Hipparchus of Nicaea)Father of Trigonometry
Timelines (that include this event)
Events in -127 MORE
