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The autumnal equinox, occurring today (Tuesday, September 22), marks the beginning of astronomical autumn in the Northern Hemisphere. At 8:05 p.m. EDT, the sun will be directly over the equator, resulting in nearly equal hours of daylight and darkness. This event signifies the transition from summer to fall, as daylight hours will continue to decrease until the winter solstice in December.
The term "equinox" originates from Latin, meaning "equal night." However, due to atmospheric refraction and the sun's position, the actual day with exactly 12 hours of daylight, known as "equilux," occurs a few days after the equinox. According to BBC Weather, this year, the equilux will happen around September 25 or 26 in the UK.
As the Northern Hemisphere enters autumn, temperatures will gradually cool. USA Today reports that while some areas in the southern and eastern United States may still experience warm weather, cooler conditions are expected to set in later this month. The change in season also brings the anticipation of fall foliage, with peak colors expected in the northern U.S. and Northeast starting in early October.
While the equinox is a global event, its cultural significance varies. Many gather at historical sites like Stonehenge to celebrate the occasion. Despite the astronomical shift, The Weather Channel notes that meteorologists consider fall to have begun on September 1, based on a three-month seasonal division for weather statistics.