21 September 2015
The autumnal equinox is at 8:22 GMT or 4:22 am EDT on Wednesday. The two satellite images below from the European Meteosat show the sun angle on Earth from June 22 near the summer solstice and then today at the same time. Notice the sun angle has changed dramatically, and the High Arctic is no longer seeing 24 hour daylight.
Below is today at the same time.