Fall, also known as autumn, lasts for three months and, in Western cultures, begins on the September equinox in the Northern hemisphere and the March equinox in the Southern hemisphere. Fall is noted for harvests, cooling temperatures, shorter days and the start of the holiday season in the West.
The autumnal equinox occurs around the third week of September and is the point on the calendar when the number of daylight hours roughly equals the number of nighttime hours (about 12 each). On this day, the sun rises at due east and sets at due west, following the celestial equator. Sunrise and sunset only align exactly with the celestial equator on the spring and fall equinox.