What is the first and last day of fall?

In the northern hemisphere, fall, or autumn, begins at the time of the September equinox, which falls between the 21st and the 24th of September inclusive, and ends at the time of the December solstice, which falls between the 20th and the 23rd of December inclusive. In the Southern Hemisphere, fall begins at the time of the March equinox, which falls between the 19th and the 22nd of March inclusive, and ends at the time of the June solstice, which falls between the 19th and the 23rd of June inclusive.