Axial precession
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In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's rotational axis. In the absence of precession, the astronomical body's orb
"Table indicating the longitude of three stars observed at different times." Compiled by Adriaan Metius, 1624.
Precessional movement as seen from 'outside' the celestial sphere
Marine sandglass MMM
Hipparchus
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Hipparchus was a Greek astronomer, geographer, and mathematician. He is considered the founder of trigonometry, but is most famous for his incidental discovery of the precession of the equinoxes. Hipp
Axial precession
…along the ecliptic. Historically, the discovery of the precession of the equinoxes is usually attributed in the West to the 2nd-century-BC astronomer Hipparchus. With improvements in the ability to calculate the gravitational force between planets during the first half of the nineteenth century, it was recognized…
Illustration based on a 19th century engraved amethyst from the Poniatowski gem collection
The figure on the left may be Hipparchus, from Raphael’s fresco The School of Athens
A 19th century artist's impression of Hipparchus
Hipparcos satellite in the Large Solar Simulator, ESTEC, February 1988