On the first day of autumn
or the fall equinox, day and night are each about 12 hours long. Therefore the
Fall Equinox or the start of autumn is when day when night and day are of equal
length making the start of Autumn for September 22, more specifically in the
Northern Hemisphere on September 22 at 10:49 A.M. EST.
Source: http://www.almanac.com/content/first-day-seasons
