This time of year, you will often hear people refer to the autumnal equinox, which took place earlier today, as the “official start of fall.” But as one of our editors wrote five years ago:
The notion of some government functionary dictating the seasons is an odd one to begin with, and in most cases, starting and ending them at solstices and equinoxes is contrary to common usage. According to the Oxford English Dictionary, autumn is “reckoned astronomically from the descending equinox to the winter solstice,” but “popularly, it comprises, in Great Britain, August, September, and October [Samuel Johnson]; in North America, September, October, and November (Webster); and in France ‘from the end of August to the first fortnight of November’ (Littré).” That’s why in Britain the summer solstice was considered “midsummer night,” not the start of summer.
It’s the same as with the decade thing: There’s no “technically” or “offiicially” or “actually” about it. A season begins whenever personal preference and common usage dictate. Today is the first day of fall — if you want it to be. And if, where you live, fall doesn’t begin until November, or if has already been fall for a month, then that’s fine too. The cycle of the seasons is among the oldest natural phenomena known to humans, and we don’t need experts or bureaucrats to know when they start and end.