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

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.

"In Chicago's canyon of tall buildings, especially in the downtown area, the sun will be framed by the rising sun, and the setting sun will be framed by those tall buildings," says Michelle Nichols, senior director of public programs at the Adler Planetarium in Chicago. "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.