The fall equinox—also called the autumn equinox—takes place every year at some time between September 21 and September 24. It marks the first day of fall in the Northern Hemisphere. (The reverse is true in the Southern Hemisphere, where the September equinox signals the first day of spring.) People have celebrated the fall equinox for centuries. In the Northern Hemisphere, the September equinox coincides with the fall harvest, and many ancient harvest celebrations take place on or around the fall equinox.