The fall equinox arrives Tuesday, Sept. 22, in the United States, marking the shift toward shorter days and the transition into autumn for the Northern Hemisphere. In several American cities, this celestial event provides a unique opportunity to witness a striking alignment between the sun and the urban landscape. As the sun rises and sets due east and west, its rays line up perfectly with streets oriented along the cardinal points, creating a phenomenon akin to the ancient solar alignments at Stonehenge.
Geoff Boeing, chair of the Department of Urban Planning and Spatial Analysis at the University of Southern California, notes that people remain deeply connected to the significance of these moments. “The things we built helped us to frame the universe in a certain way,” Boeing said. “Humans still connect with how special it feels.”
In Chicago, the effect is particularly dramatic due to the city’s dense skyline. Michelle Nichols, senior director of public programs at the Adler Planetarium, explained that the towering buildings frame both the rising and setting sun. This visual spectacle, known as “Chicagohenge,” occurs on narrow windows of one or two days each year when the sun travels directly down east-west thoroughfares like Madison and Kinzie streets.
According to Nichols, witnessing the event requires only a wide street running east to west, with some elevation proving helpful. The alignment is made possible by Chicago’s street grid, which adheres closely to north, south, east, and west compass bearings.
Other grid-based cities, including Washington, D.C., and Phoenix, also offer prime vantage points for observing similar solar alignments. Nichols highlighted that these urban canyons allow residents and tourists alike to gather downtown and experience the intersection of architecture and astronomy.
Boeing pointed out that aligning cities with the heavens is an ancient tradition. He referenced Tenochtitlan, the Aztec precursor to modern Mexico City, as an example of early urban planning that incorporated astronomical knowledge. “Especially thousands of years ago, a lot of early cities would be developed with these almost cosmic urban plans,” he said, noting that these designs often served religious and spiritual purposes by mirroring points in the sky.
While modern cities were not necessarily designed with cosmological intent, the byproduct of their grid layouts still produces these annual events. “Even if we didn’t do it intentionally, we’re still getting the same side effects at least once or twice a year,” Boeing observed.
As Nichols summarized, although contemporary society no longer relies on these alignments for navigation or calendar-keeping, they serve as powerful reminders that “the sky really is still up there.”
Leave a Reply