What the equinox 'henge' effect tells us about U.S. cities

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Fresh Air Wild Card with Rachel Martin It's Been a Minute Embedded Get NPR+ More Podcasts & Shows Search Newsletters NPR Shop Get NPR+ Tiny Desk New Music Friday All Songs Considered Music Features About NPR Diversity Support Careers Press Ethics Equinox brings ‘henge’ effect to cities laid out on a grid The fall equinox, which arrives Tuesday in the U.S., brings shorter days, and chances to witness alignment between Earth and the sun. It's a modern version of ancient observances of a celestial shift. National What the equinox 'henge' effect tells us about U.S. cities September 21, 20263:50 PM ET By Bill Chappell The sun creates a "Chicagohenge" effect in Chicago, as the sun rises and falls straight down streets such as Kinzie and Madison one or two days each year, as seen here on Sept. 22, 2017. Bilgin S. Sasmaz/Anadolu Agency/Getty Images hide caption The fall equinox brings shorter days, and the change of seasons. In some U.S. cities, it's also a chance to witness the striking alignment between the sun and Earth, as sunrises and sunsets align with city streets running east and west. It's a modern version of ancient observances of a celestial shift, like sunrise at Stonehenge. "Humans still connect with how special it feels," says Geoff Boeing, who studies city design as the chair of the Department of Urban Planning and Spatial Analysis at the University of Southern California. "The things we built helped us to frame the universe in a certain way," Boeing adds. In this case, that framing is literal. Take Chicago, for instance. "The effect itself is accentuated by the height of the buildings and the width of the streets." Fans of the phenomenon call it "Chicagohenge," after England's famously solar-aligned Stonehenge. It occurs thanks to Chicago's street design that follows the cardinal points of the compass: north, east, west and south. All you need to see it, Nichols says, is a wide street running east and west. A bit of elevation might also help. The 2026 fall equinox arrives on Sept. 22 in the U.S., with the precise time falling in the evening, according to the U.S. Naval Observatory. It means roughly equal hours of day and night, as autumn begins in the Northern Hemisphere and spring starts in the Southern Hemisphere. Other cities that are laid out on a grid, such as Washington, D.C. and Phoenix can also offer good chances to spot a "henge" moment. Humans have long laid out cities in ways that correspond to the skies, and cardinal points of the compass. "It's interesting because this is a very old phenomenon," Boeing says. "Especially thousands of years ago, a lot of early cities would be developed with these almost cosmic urban plans." Marking celestial change was a deeply religious and spiritual experience for people, he says, "and their cities would be designed almost like cosmological maps to follow it, where you could have points in the city that corresponded to certain stars in the night sky." For example, Tenochtitlan, the Aztec precursor of today's Mexico City, was "carefully planned with astronomical knowledge," as a 2021 academic paper noted. Photographers, tourists and residents gather downtown to view "Chicagohenge" on March 22, 2025, in Chicago. Scott Olson/Getty Images hide caption In modern cities, such points are often towers of steel and concrete, and asphalt streets. And their alignment with celestial features is more a byproduct of a grid layout than a cosmological goal. But, Boeing says, that hardly matters. "Even if we didn't do it intentionally, we're still getting the same side effects at least once or twice a year." As Nichols puts it, "We don't rely on these alignments to tell us things, but they are really great reminders that, hey, the sky really is still up there." A graphic shows how faithfully different U.S. cities follow a compass grid in their streets' layout. Courtesy Geoff Boeing hide caption Cities like Chicago and Denver are good candidates for viewing an equinox because of their faithfulness to the compass, according to Boeing, who has published a comparative analysis of cities' street grids. He says the cities "are really good examples of this kind of 19th century urban planning, spatial logic that spread across the Midwest and the Great Plains during the Great Westward expansion in the U.S. in the 19th century, that was really aligned with orthogonal grids." Grids made it easier to buy and sell land, Boeing says. It also made it easier to map out infrastructure like railroads. Some cities use a grid that's aligned not with the compass but with local geography, like waterways or mountains. That's why another famous "henge"— "Manhattanhenge" — doesn't occur on the equinox dates; neither does San Francisco's stunning "California Henge." Even if your local streets "are all sort of wonky with the directions that they go," Nichols says, you might spot an interesting alignment. "You just have to pay attention," she says. Instagram and other photo-sharing apps have made the equinox something of a media darling, the Adler Planetarium's Nichols says, because of the dramatic scenes it can create. During pandemic lockdowns, she adds, the equinox gained popularity for another reason. "The opportunity to experience an effect together while still being apart," she says. "That was extraordinarily important to people." But Nichols says people should also be careful for their own safety, as they seek to create dramatic images and memories. "Just be mindful," she says. "Don't walk out in the middle of the street to be able to take the perfect photo. You can do this from the sidewalks, on the side. It's totally fine." And if you're driving in the morning or afternoon around the time of the equinox, it's good to remember that on east-west streets, you're likely to get a blast of sunshine directly in your face, with glare that makes it hard to see other cars, pedestrians and traffic signals "You do see traffic buildups and backups because of the location of the sun in the sky," Nichols says. NPR does not offer or accept money for coverage or interviews. Anyone who makes such an offer or request is not an NPR employee and does not represent NPR. Sponsor Message Become an NPR sponsor