On September 19th we have "Talk Like A Pirate Day" (a fave of Jeff's)
and then September 22nd is the autumnal Equinox.
In the Northern Hemisphere, the fall equinox marks the first day of fall (autumn) in what we call astronomical seasons. There's also another, more common definition of when the seasons start, namely meteorological definitions, which are based on average temperatures rather that astronomical events.