The 2012 September equinox comes on September 22, at 9:49 a.m. CDT (14:49 Universal Time).
On the equinox, night and day are nearly exactly the same length – 12 hours – all over the world. This is the reason it’s called an “equinox”, derived from Latin, meaning “equal night”.
The September equinox occurs the moment the sun crosses the celestial equator – the imaginary line in the sky above the Earth’s equator – from north to south.
Summer is gone, winter is coming.