In the Northern Hemisphere, autumn is between the autumnal equinox that begins on Sept. 22 or 23 and the winter solstice, which is Dec. 21 or 22. In the Southern Hemisphere, autumn is between March 20 or 21 and June 21 or 22.
The temperature transition in autumn from summer heat to winter cold only occurs in middle and high latitudes. In equatorial regions, temperatures usually have very little variation during the year. In polar regions, autumn is very short. In the central and eastern United States and Europe, a relatively common autumn phenomenon is an Indian summer, which is a period of unseasonably warm weather that sometimes continues until late October or November.