autumn equinox 2021

Autumn Equinox 2021: Timing, Weather and More for First Day of Fall in Illinois

According to the Adler Planetarium in Chicago, the autumn equinox marks the point when "daytime and nighttime are roughly equal in length."

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Fall's return officially begins Wednesday, and the Chicago area will see several signs of the new season, including the return of cooler temperatures.

The first official day of fall is Sept. 22. The autumnal equinox, also referred to as the September or fall equinox, arrives at 2:21 p.m. Wednesday for the Northern Hemisphere, according to the Old Farmer's Almanac.

According to the Adler Planetarium in Chicago, the autumn equinox marks the point when "daytime and nighttime are roughly equal in length."

"If you’re in the Chicago area," Karen Donnelly writes in the Adler Skywatch, "you may be noticing that the Sun rises later and later—and sets earlier and earlier—each day this month."

"Actually, in the Northern Hemisphere the Sun has been rising later and setting earlier since the summer solstice," Donnelly writes, "but from the autumnal equinox on, the night-sky time will last longer than the daylight time until the next vernal equinox. We’ll keep gaining dark-sky viewing time until the winter solstice on Dec. 21."

It also marks the appearance of Chicagohenge in Chicago, this year happening between Sept. 22 and 25. Donnelly describes the twice-yearly event as a celestial phenomenon marking the point when you can see the sun rise or set directly between downtown buildings on east- and west-facing streets.

This year, cooler temperatures also will signal the start of fall in the Chicago area.

On Wednesday and Thursday, showers are possible throughout the area, with high temperatures in the mid-60s and lows dropping to near 50 degrees.

Strong winds Wednesday could bring gusts of up to 45 mph near Lake Michigan Wednesday afternoon and into Thursday morning. Flooding and very dangerous waves are expected along the lakefront.

Things should begin to warm back up a bit by Friday, according to extended forecast models.

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