Equinox

Equinox (1) either of the 2 times each year when day and night are of equal length. The spring, or vernal equinox occurs in Mar., the autumnal equinox in Sept., (2) either of the 2 intersections of the ecliptic and equator on the celestial sphere. In other words, the equinoxes are the points at which the Sun crosses the celestial equator.