As of 15 minutes ago, autumn has officially arrived! The autumnal equinox occurred at 15:44 UTC (or 9:44am CDT) this morning. An equinox, as defined by Wikipedia, is "the moment in time (not a whole day) when the center of the Sun can be observed to be directly above the Earth's equator." Further, "the center of the Sun will spend a nearly equal amount of time above and below the horizon at every location on Earth and night and day will be of nearly the same length." Checking the sunrise and sunset for Memphis today, sunrise was at 6:49am CDT and sunset will be at 6:53pm CDT. The closest we will be to exactly 12 hours of daylight and darkness (not counting civil twilight) will be Thursday/Friday of this week.
For more on equinoxes, check out this article: http://en.wikipedia.org/wiki/Equinox
Our weather for the first week of fall is pretty much right on track! Mostly sunny skies and highs in the lower to mid 80s are expected all week, while lows will run in the 60s.