An equinox occurs twice a year when the sun is directly above the equator, resulting in nearly equal day and night lengths across the globe. The two equinoxes are known as the vernal equinox, which happens around March 20 or 21, and the autumnal equinox, occurring around September 22 or 23. During an equinox, the tilt of the Earth's axis is such that it is neither tilted toward nor away from the sun. This phenomenon marks the change of seasons, transitioning from winter to spring in March and from summer to fall in September.