Fall Equinox to Frame Sunrises and Sunsets in Grid-Planned U.S. Cities

Chicago is the best-known case. Michelle Nichols, senior director of public programs at the Adler Planetarium in Chicago, said that in the city's downtown canyon of tall buildings, the rising and setting sun is framed by the structures on either side. "The effect itself is accentuated by the height of the buildings and the width of the streets," she said. Fans of the phenomenon call it "Chicagohenge," after England's Stonehenge, whose stones align with the sun. What is needed, Nichols said, is a wide street running east and west; a bit of elevation may also help.

Chicago's street design follows the cardinal points of the compass, north, east, west and south. Washington, D.C., and Phoenix, which are also laid out on grids, offer similar chances to spot a "henge" moment.

Geoff Boeing, who studies city design as chair of the Department of Urban Planning and Spatial Analysis at the University of Southern California, said the effect is a very old phenomenon in a modern form. "Humans still connect with how special it feels," he said. "The things we built helped us to frame the universe in a certain way."

Thousands of years ago, Boeing said, many early cities were developed with "almost cosmic urban plans," and marking celestial change was a deeply religious and spiritual experience. A 2021 academic paper noted that Tenochtitlan, the Aztec precursor of today's Mexico City, was "carefully planned with astronomical knowledge." In modern cities the aligned points are steel and concrete towers and asphalt streets, and the alignments are largely a byproduct of grid layouts rather than a cosmological goal. Boeing said 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."

Boeing, who has published a comparative analysis of cities' street grids, said Chicago and Denver are strong candidates for equinox viewing because of their faithfulness to the compass. He described them as good examples of 19th century urban planning that spread across the Midwest and the Great Plains during westward expansion and was aligned with orthogonal grids, which made land easier to buy and sell and infrastructure such as railroads easier to map.

Two better-known events do not fall on the equinox dates. Manhattanhenge and San Francisco's "California Henge" occur at other times because those street grids are aligned with local geography, such as waterways or mountains, rather than with the compass, according to Boeing.

Nichols said Instagram and other photo-sharing apps have made the equinox something of a media favorite because of the dramatic scenes it creates, and that during pandemic lockdowns it gained popularity as a chance to experience an effect together while staying apart. She also urged care. "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," she said. Even where local streets run at odd angles, she added, an interesting alignment may still appear: "You just have to pay attention."