I was surprised reading this, A CUP OF JO: First day of fall, that the first day of fall is actually tomorrow, the 23rd. I thought it always fell on the 21st! According to this, the date moves around quite a bit. Usually Fall/Autumn starts on September 22, but in 2011, 2014 and 2015, it falls :) on the 23rd.
Good to know.
(Image linked to from A Cup of Jo.)