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Article
Precession of equinoxes
Article By:
Pasachoff, Jay M. Hopkins Observatory, Williams College, Williamstown, Massachusetts.
Last reviewed:January 2022
DOI:https://doi.org/10.1036/1097-8542.542300
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- Precession of equinoxes, published December 2019:Download PDF
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A slow change in the direction of the axis of rotation of the Earth as well as a very small change in the orientation of the Earth's orbit around the Sun. As a consequence of the precession of equinoxes, both the celestial equator (the projection of the terrestrial equator onto the sky) and the ecliptic (the projection of the Earth's orbit onto the sky) move slowly in time, and, consequently, so do their intersections, the vernal and autumnal equinoxes (Fig. 1). The Greek astronomer and mathematician Hipparchus is credited with the discovery of the phenomenon of the precession of equinoxes in the second century BCE. See also: Celestial sphere; Ecliptic; Equator; Equinox
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