precession of the equinoxes
noun
- the slow retrograde motion of equinoctial points along the ecliptic.
- the resulting earlier occurrence of equinoxes in each successive sidereal year.
- As the earth rotates about its axis it responds to the gravitational attraction of the sun upon its equatorial bulge, so that its axis of rotation describes a circle in the sky, with a period of about 26,000 years. The precession of the equinoxes was discovered by Hipparchus in circa 125 bc, when the vernal equinox was in Aries