Equinoxes

A solar equinox is a moment in time when the Sun appears directly above the equator, rather than to its north or south. On the day of the equinox, the Sun appears to rise directly east and set directly west. This occurs twice each year, around 20 March and 23 September.

Hipparchus (; , ;  BC) 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. Hipparchus was born in Nicaea, Bithynia, and probably died on the island of Rhodes, Greece. He is known to have been a working astronomer between 162 and 127 BC.

Al-Battani (before 858929), archaically Latinized as Albategnius, was a Arab Muslim astronomer, astrologer, geographer and mathematician, who lived and worked for most of his life at Raqqa, now in Syria. He is considered to be one of the greatest and most famous of the astronomers of the medieval Islamic world.

gravity-induced, slow, and continuous change in the orientation of an astronomical body's rotational axis

Length of time

point defined via celestial coordinates

4th century Chinese astronomer and writer