September 22, 2000

     First Day of Autumn

Fall officially begins at 12:27 p.m. today.  Equinox means equal night.  The first official day of autumn, the autumnal equinox, occurs on Sept. 22 or 23 each year in the Northern Hemisphere.  Then, the Sun is in position so that every place on Earth receives exactly 12 hours of sunshine and 12 hours of night.

However, there is an exception.  Sunrise occurs at 6 a.m., local solar time, and sunset is at 6 p.m. at all places on Earth except at the poles, where the Sun remains on the horizon all day, traveling one complete circuit of the horizon in 24 hours.

On the autumnal equinox at all latitudes, except at the two poles, the Sun rises at a point due east on the horizon and sets at a point due west.  In the Northern Hemisphere we will notice that the Sun continues to shine for an increasingly shorter time each day as the nights get longer until the winter solstice on Dec. 21.

The astronomical first day of fall, the autumnal equinox, does not coincide with our biological fall.  Signs of fall have been with us in Minnesota since July, and each year many fall signs, such as bird migrations and fall foliage colors, come on strong about the first of September.