The date is Sep. 22, 2022, the date of the fall equinox.  Although this is supposed to be the day of equal day and night, we know it's not exactly correct.  We measure daytime from sunrise to sunset, measured as the first and last light from the sun peaking over the horizon.  When we include sunrise and sunset plus atmospheric refration, at mid latitudes daylight wins by about 10 minutes (not even counting twilight).

nass news 2022 sep chicagohenge TimHara
Chicagohenge photo by Tim Hara

But something magical happens as the sun sets due west on the equinox in Chicago. The sunset direction matches the direction of the Chicago grid of East-West streets.  The effect is known as Chicagohenge.

From the Adler Planetarium website ( "Chicagohenge occurs twice a year and happens when the Sun directly lines up with Chicago’s east-west facing streets ... To fully understand Chicagohenge, you have to be aware of the two main factors that cause it: Chicago’s grid plan and equinoxes...The present-day Chicago grid system can be attributed to the Public Land Survey System -- a surveying method created in 1785 that was used to divide land for selling and settling. But this style of city design has been around since the dawn of civilization and can be found in the ruins of ancient Rome, Greece, and others [sometimes creating solar alignments in these cities such as Manhattan Henge] ... Fun fact: Chicago’s streets line up almost perfectly with the cardinal east and west directions on a compass. This in turn, sets up the perfect stage for Chicagohenge to take place."

The Planetarium Blog continues. "Since the Earth’s axis is tilted, sunlight is not always distributed equally. At any given point, one-half of the Earth is tilted towards the Sun more than the other. As the Earth orbits around the Sun, the part that was tilting away from the Sun begins to be the part that is facing towards the Sun. This is why we have seasons! ... There are two equinoxes each year, one that marks the start of spring (Spring Equinox) and one that marks the end of summer (Autumn Equinox). Thanks to Chicago’s perfectly lined grid system, the bi-annual equinoxes mark a time when the Sun rises and sets directly in line with Chicago’s east and west streets, causing Chicagohenge! ... Finding a place to spot Chicagohenge is a no-brainer! Simply find one of Chicago’s east-west facing streets, plop a seat, and enjoy the view."