Autumnal Equinox
Also:Sept 22-23 of each year

In the Northern Hemisphere, the Autumnal Equinox occurs in late September, generally the 22 or 23, and marks the beginning of the season of autumn, or fall. In the Southern Hemisphere, this date marks the Spring Equinox. The Autumnal Equinox in the Southern Hemisphere occurs in March.

Time of Daylight
On the Autumnal Equinox, the sun is above the horizon for about the same time as it is below the horizon. There is some minor variation due to time zones. This means that on the Autumnal Equinox, as well as the Spring Equinox, the Earth experiences an equal amount of day and night.

Many cultures hold celebrations or ceremonies to mark the Autumnal Equinox. Neopaganist and Wiccans celebrate Mabon. This is a celebration of harvest and winter preparation. Some Asian cultures also celebrate this day by visiting loved ones, ancestral grave sites and holding reunions.

Harvest Moon
The Harvest Moon occurs on or near the Autumnal Equinox. The Harvest Moon is the full moon that occurs closest to the Autumnal Equinox. The Harvest moon is so called because it offers light so farmers can extend their harvesting time.

Source: Michael Kozlowski