Ask Patch: What is Autumnal Equinox?

We've all noticed that the days are becoming shorter and the temperatures a little crisper, but when precisely does summer give way to fall? 

For answers we turned that old standby, the Farmers' Almanac. At 9:49 a.m. this Saturday, Sept. 22, the northern hemisphere officially said goodbye to summer with the coming of the Autumnal Equinox, the moment when the sun crosses the equator. What does that mean? Less daylight for us, and more for our neighbors in the earth's southern hemisphere.

One important note: The days have been growing shorter since Summer Solstice in June, the longest day of the year, but until this morning the days were still longer than the nights. Autumnal Equinox signals a critical turning point when dark starts to win out over daylight. Nights will continue to lengthen until Winter Solstice on Dec. 21, 2012, the shortest day of the year. After Winter Solstice passes, the days will get longer again, a signal that spring is on the way.