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.

The exact time of the fall equinox changes slightly each year. This year, the equinox arrives Sept. 22 at 8:43 a.m. Eastern time.

The autumnal equinox brings fall to the Northern Hemisphere today as the sun passes directly over the equator at noon. But are day and night actually equal length today?

During an equinox, places around the globe experience nearly equal amounts of daytime and nighttime. The second occurrence this year happens on Sunday.

If you get up early enough, you can experience an equinox sunrise. The autumnal equinox heralds the arrival of fall in the northern hemisphere.