Updated September 21, 2022 at 4:45 PM ET
Westbound traffic on many Chicago streets may come to a stop after 6:40 p.m. CDT on Wednesday as drivers snap pictures over dashboards, passengers with smartphones in hand lean out of windows, and pedestrians set up tripods in the middle of some busy roadways — all to capture the incredible image of a burnt orange sun setting exquisitely framed by a canyon of skyscrapers.
It's known as "Chicagohenge," one of two days a year when the sun rises and sets in perfect alignment with the city's east-west streets. Chicago's street grid corresponds almost exactly with the directional points of the compass.
It happens in other cities with gridded streets, too — Manhattanhenge, for example — but Chicago is unique in that the phenomenon takes place every year on the spring and fall equinoxes.
According to an explanation on the website of Chicago's Adler Planetarium, the twice yearly event occurs mainly due to the fact that "Chicago's streets line up almost perfectly with the cardinal east and west directions on a compass."
On all but two days of the year, because "the Earth's axis is tilted, sunlight is not always distributed equally" between the northern and southern hemisphere, the explanation continues. One hemisphere will have more daylight than the other. But "there are two times during the year when the Earth's equator receives most of the sunlight... (and) our planet's Northern and Southern Hemispheres experience equal amounts of day and night—hence the term equinox."
So, "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," the Adler planetarium says.
In 2019, with perfect early fall weather of partly cloudy skies and temperatures in the 60s, I timed my departure from NPR's Chicago bureau on Michigan Avenue at about 6:20 p.m. and walked east up an incline on Randolph Street, across from the north end of Millennium Park.
Several dozen amateur (and maybe professional) photographers had already set themselves up on prime real estate in the road's median, on curbs and along a railing on an overpass above where the street separates into upper and lower levels.
But others, myself included, just dodged taxicabs, cars, and buses and stepped into the bike line or the street to capture the spectacular moment. It's one of the rare instances I've experienced when hurried city drivers didn't seem to mind stopping for the many people moving in and out of traffic as they stared into a blinding orange glare.
In the same way our Washington, D.C., colleagues attach the word "gate" to designate the scandal du jour, Chicagohenge is not really a henge. It gets its name from Stonehenge, the monument of massive rocks in England that scientists believe was erected more than 4,000 years ago. On certain dates, the rising and setting sun lines up with the stones, leading some to suggest that Stonehenge could have been built by early astronomers.
The next date to catch Chicagohenge is when the weather is almost certain to be less enjoyable: March 20, 2023.
Copyright 2022 NPR. To see more, visit https://www.npr.org.
