And before you knew it, the summer is over. The 2010 September Equinox falls on 23 September 03.09. The Fall Equinox is the moment when the night and day span exactly the same amount of hours.
An equinox occurs twice a year, when the tilt of the Earth's axis is inclined neither away from nor towards the Sun, the center of the Sun being in the same plane as the Earth's equator. The term equinox can also be used in a broader sense, meaning the date when such a passage happens….An equinox happens each year at two specific moments in time (rather than two whole days), when there is a location on the Earth's equator where the center of the Sun can be observed to be vertically overhead (in astronomical terms, the subsolar point), occurring around March 20/21 and September 22/23 each year….On a day of the equinox, the center of the Sun spends a roughly equal amount of time above and below the horizon at every location on the Earth, night and day being of roughly the same length.
If you ever have the chance, go check out the Equinox in Chichen Itza.