In the Northern Hemisphere, the official start of fall is Friday, September 22 at 4:02PM EDT. This day is also called the Autumnal equinox.  By definition, Equinox means “equal night”; night and day are about the same length.  

Fall is also defined by nights of below-freezing temperatures combined with days of temperatures below 70 degrees Fahrenheit.  From Friday on, the temperatures begin to drop and the days start to get shorter than the nights.