what is equinox

An equinox is an event that occurs when a planets subsolar point passes through its Equator. On Earth, there are two equinoxes every year: one around March 21 and another around September 22. During an equinox, both the Northern and Southern Hemispheres experience roughly equal amounts of daytime and nighttime. The word "equinox" is derived from two Latin words - aequus (equal) and nox (night), signifying the nearly equal hours of day and night during this event. The equinoxes are sometimes regarded as the start of spring and autumn, and they mark the astronomical beginning of these seasons, depending on the hemisphere. Equinoxes occur twice a year when the sun is directly above the equator, heralding the beginning of spring and autumn. The modern definition of equinox is the instant when the Suns apparent geocentric ecliptic longitude is 0° (northward equinox) or 180° (southward equinox) .