Autumn has officially begun! In the Northern Hemisphere, the autumnal equinox falls on September 23 this year, marking the beginning of autumn and the Earth and Sun"s unique positions. Today is one of the two moments in the year when day and night are equal in length, thanks to the Sun"s location exactly above the Equator. The same celestial phenomenon applies to the Southern Hemisphere, but it is their vernal equinox as they head into spring.