Fall Equinox 2021

The autumnal equinox occurs every September in the Northern Hemisphere, marking the beginning of fall, which is September 22 in 2021. There are two equinoxes a year. The autumnal equinox, also known as the fall equinox and the September equinox, occurs in September, while the vernal equinox occurs in March. After the autumnal equinox, the days start getting shorter, and the nights get longer.

In most of the U.S., September is the time when we reluctantly stash our pool tubes and start brainstorming Halloween costume ideas. It's also when the fall equinox officially marks the end of one season and the start of the next. Here's what that means, the difference between an equinox and a solstice, and when to expect the first day of fall in 2021.

What is an equinox?

An equinox is the point at which the sun sits directly above the earth's equator, and day and night are of approximately equal length across the world. The word "equinox" is derived from two words: aequus, which is Latin for “equal,” and nox, Latin for “night.”

It's also the halfway point between the summer solstice on June 20, 2021, and the winter solstice that occurs on Tuesday, December 2021.

When is the first day of fall 2021?

Wednesday, September 22, is the first official day of fall. This also makes it the last day of summer, so start refreshing your sweater collection now.

It's worth noting that this is the beginning of autumn in the Northern Hemisphere; in the Southern Hemisphere (where only 1 percent of the world's population lives) the equinox dates are reversed. In the Southern Hemisphere, fall begins in March and spring arrives in September.