The official first day of fall, otherwise known as the autumnal equinox, is this weekend in the Northern Hemisphere. According to Encyclopedia Britannica, it is one of only two days, the other being the vernal equinox, when the sun is directly above the Equator, essentially dividing night and day into equal portions.

Many people consider the autumnal equinox on Sunday as the official end of summer and the first day of fall. If you were waiting on the autumnal equinox for fall weather, though, you may have to keep waiting.