first-day-of-fall

When does fall begin?

• On the 21st (today!), as do the other seasons2
• On the 22nd, the autumnal equinox, when the days and nights are the same length3
• On the 1st, because defining seasons based on shifting solar events or their approximations is too variable
• It starts whenever the trees change color and the leaves begin to fall7
• It starts at the first cup of hot apple cider... so, yesterday