When is the First Day of Fall? Autumnal Equinox This Week to Mark Start of Season

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The days of summer are ending, and soon it'll be fall - a season marked by colorful foliage, apple picking, pumpkins and much more.

Weather-wise, it might already feel like fall outside, at least in some areas experiencing cooler temperatures. However, the season doesn't officially begin Thursday, when the autumnal equinox takes place.

The autumnal equinox, also referred to as the September or fall equinox, signals the shift between summer and fall. The season will precisely arrive at 8:04 p.m. Sept. 22 for the Northern Hemisphere, according to the Old Farmer's Almanac.

The equinox marks the point when "daytime and nighttime are roughly equal in length," according to Chicago's Adler Planetarium.

The planetarium also said that the sun will rise later and set earlier throughout the month following the equinox.

As the hours of sunlight lessen, signs of fall will begin to emerge. According to the almanac, leaves start to change colors and drop due to the amount of daylight and photosynthesis, rather than weather conditions, such as temperature.

Sept. 22 also will signify the appearance of the Chicagohenge, the city's celestial event that happens only twice a year.

According to the planetarium, the Chicagohenge showcases the point when the sun directly lines up with Chicago’s east- and west-facing streets. Chicagoans will be able to see the phenomenon until Sept. 25, the planetarium said.

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