Explanation

An equinox is commonly regarded as the instant of time when the plane (extended indefinitely in all directions) of Earth’s equator passes through the center of the Sun.[3] This occurs twice each year: around 20 March and 23 September. In other words, it is the moment at which the center of the visible Sun is directly above the Equator. The word is derived from the Latin aequinoctium, from aequus (equal) and nox (genitive noctis) (night). On the day of an equinox, daytime and nighttime are of approximately equal duration all over the planet.