Happy Autumnal Equinox!
The 2011 September equinox comes on September 23 at 4:05 a.m. CDT. It falls at 9:05 Universal Time (GMT
On the first day of fall—the autumnal equinox—day and night are each about 12 hours long (with the actual time of equal day and night, in the Northern Hemisphere, occurring a few days after the autumnal equinox). The Sun crosses the celestial equator going southward; it rises exactly due east and sets exactly due west.
September 23, 5:05 A.M. EDT
The four seasons are determined by changing sunlight (not heat!)—which is determined by how our planet orbits the Sun and the tilt of its axis.
The Autumnal Equinox signals the end of the summer months and the beginning of winter. At this time of year, days have been shortening since the Summer Solstice some three months earlier, and the Equinox is the point where nights reach the same length as days. After this point, the Sun will shine lower and lower on the horizon until the Winter Solstice in about three months’ time.
The equinoxes represent the points where the direction of poles are at a right angle to the Sun. They represent the point of transition from summer to winter, or from winter to summer. The Autumnal Equinox occurs in late September, and is named for the fact that it marks the end of summer and the entrance into winter of the northern hemisphere
