Autumnal Equinox marks first day of fall

The autumnal equinox arrives Tuesday, September 22, 2026, with the U.S. Naval Observatory placing the precise moment in the evening. The sun crosses the celestial equator so the Northern Hemisphere moves into autumn and the Southern Hemisphere into spring, producing roughly equal hours of day and night. In some U.S. cities the equinox also lines up with street grids to create a striking sunrise or sunset framing known as "Chicagohenge," visible on wide east, west streets such as Kinzie and Madison. Michelle Nichols of the Adler Planetarium says tall buildings and street width accentuate that framing, and Geoff Boeing of the University of Southern California links the effect to long histories of cities aligned with the skies. Other grid cities like Washington, D.C., and Phoenix can produce similar "henge" moments once or twice a year. Photographers and residents often gather downtown to view and photograph these alignments around the equinox.