what is the fall equinox

The fall equinox, also known as the autumnal equinox, is one of the two moments in the year when the Sun is exactly above the Equator, and day and night are of equal length. It marks the beginning of autumn in the Northern Hemisphere and occurs around September 22 or 23, as the Sun crosses the celestial equator going south. In the Southern Hemisphere, the equinox occurs on March 20 or 21, when the Sun moves north across the celestial equator. The word "equinox" is derived from the Latin words "aequus" (equal) and "nox" (night), signifying the nearly equal hours of day and night during this time. The fall equinox also triggers changes in nature, such as the vibrant colors of autumn leaves as chemicals in the leaves shift.