It varies from time to time. This year, fall equinox began September 22. It will end on December 20 as winter will begin on December 21.
Check out the solstice & equinox dates until 2020 at Greenwichmeantime.com.
Equinoxes are opposite on either side of the equator, so the autumnal (fall) equinox in the Northern Hemisphere is the spring (vernal) equinox in the Southern Hemisphere and vice versa.
Autumn flies by in a flash, so take advantage of the crisp weather and beautiful foliage with this list of fun activities to do in the fall shared by Realsimple.com.