When does fall/autumn begin?
Fall/autumn begins at the autumnal equinox. During summer, the sun is always directly above somewhere in the northern hemisphere, the autumnal equinox occurs when the sun crosses the equator to be directly above some point in the southern hemisphere. This is true only for those in the northern hemisphere, but a similar principle applies to the southern hemisphere. Because the calendar year is always a whole number of days, whereas the solar year isn’t, the calendar time that the autumnal equinox happens varies, but it is usually on September 22 or 23. More information at http://aa.usno.navy.mil/data/docs/EarthSeasons.
