Equinox

From the Latin aequinoctium, equal night; occurs when the center of the Sun is directly over Earth’s equator. The sun crosses the equator twice each year, once at the vernal equinox when it enters 0° Aries and again at the autumnal equinox when it enters 0° Libra. The days and nights are of equal duration all over the world on equinoctial dates. The vernal equinox occurs on the first day of spring, the autumnal equinox on the first day of autumn.