Definition

One of the two points of intersection of the ECLIPTIC and the CELESTIAL EQUATOR, occupied by the SUN when its DECLINATION is zero. That point occupied on or about March 21, when the SUN's DECLINATION changes from south to north, is called vernal equinox or first point of Aries; that point occupied on or about September 23, when the DECLINATION changes from north to south, is called autumnal equinox or first point of Libra. Also called equinoctial point.