The autumnal equinox happened today at 5:05 a.m. ET. It marks the beginning of autumn in the northern hemisphere and spring in the southern hemisphere.
It’s the time of year when temperatures start to drop and the days start to get shorter.
Every year there are two equinoxes, one in March that marks the beginning of spring and one in September that marks the beginning of fall.
National Geographic explains:
The autumnal equinox and vernal equinox are also the only days of the year when a person standing on the Equator can see the sun passing directly overhead. On the Northern Hemisphere's autumnal equinox, a person at the North Pole would see the sun skimming across the horizon, signaling the start of six months of darkness. On the same day, a person at the South Pole would also see the sun skim the horizon, beginning six months of uninterrupted daylight.
Equinoxes explained:
http://www.youtube.com/watch?v=GxeFf7OACEQ
