The First Day of Fall article says that fall officially begins at September 22, 2008 at 11:44 am EDT. There’s some more information there including the reminder to put fresh batteries in your smoke detectors today!
Wikipedia’s Equinox entry says that equinox (from the Latin words aequus/equal and nox/night) can refer to the moment when the Sun is positioned directly over the Earth’s equator OR the apparent position of the Sun at that moment or the time at which the vernal point, celestial equator, and other such elements are taken to be used in the definition of a celestial coordinate system. Click through for much more Equinoxical information that appears in dire need of some editing for readability.
The outlook for fall on A Bright Spot Opposite the Sun relates:
Astronomers call Monday the autumnal equinox. Equinox means roughly “equal night”, which isn’t quite the case on Monday. The sun will rise on Monday at 7:34 AM and set at 7:41, making the day about seven minutes longer than the night. It isn’t until Thurs., Sept. 25 that the sun sets exactly twelve hours after it rises. On Monday, the day is a bit longer than the night because the sun is a disk, and sun rise and set are measured from the very top part of the sun. Anyway, it’s just a matter of minutes.
But on the equinox one thing is true: the sun rises due east and sets due west for every observer on earth. For us in West Michigan, where most of the roads are laid out east-west and north-south like the rulings on a sheet of graph paper, the equinox sun rise and set can be blinding on the commute to and from work. Take an extra pair of sunglasses with you in the car.
OK class, how about the Fall Color slideshow courtesy the Absolute Michigan group on Flickr??!!