今日秋分（Autumn Equinox）！

Autumnal equinox, two moments in the year when the Sun is exactly above the Equator and day and night are of equal length; also, either of the two points in the sky where the ecliptic (the Sun’s annual pathway) and the celestial equator intersect. 

In the Northern Hemisphere the autumnal equinox falls about September 22 or 23, as the Sun crosses the celestial equator going south. In the Southern Hemisphere the equinox occurs on March 20 or 21, when the Sun moves north across the celestial equator. According to the astronomical definition of the seasons, the autumnal equinox also marks the beginning of autumn, which lasts until the winter solstice (December 21 or 22 in the Northern Hemisphere, June 20 or 21 in the Southern Hemisphere).

Folllowing is a passage on Autumn Equinox from fox10phoenix.com.

Kelly Hayes — This week marks the official start of fall, as the Northern Hemisphere bids farewell to warmer weather and ushers in cooler temperatures, fall foliage and all things pumpkin spice. 

The autumnal equinox of 2021, also known as the September equinox or fall equinox, is on Wednesday, Sept. 22, according to the Farmer’s Almanac. The date marks the start of fall in the Northern Hemisphere and spring in the Southern Hemisphere. 

On the equinox, daytime and nighttime are roughly equal in length.

What time is the 2021 autumnal equinox?

The autumnal equinox officially arrives at 3:20 p.m. ET on Wednesday. 

During the equinox — which occurs twice per year — the sun crosses what’s known as the "celestial equator," or an extension of Earth’s equator line into space, the Farmer’s Almanac explains.

The autumnal equinox occurs when the sun crosses the equator from north to south. The vernal equinox, or the start of spring, happens when it moves from south to north.

A full moon, known as the Harvest Moon, preceded the start of fall. The moon appeared full for about three days, starting on Sunday morning through Tuesday morning.