MITCHELL, SD (Mitchell Now) — Cooler mornings, changing leaves, football games and harvest season are signs that fall is approaching in South Dakota. But the season has an official astronomical starting point.
The autumnal equinox occurs at 7:05 p.m. CDT Tuesday, Sept. 22, 2026, marking the official beginning of fall in Mitchell and the rest of the Northern Hemisphere.
Here are four things to know about the first day of fall.
The Equinox is Actually a Moment
Although Sept. 22 is considered the first day of fall, the equinox itself happens at a precise moment. It occurs when the sun crosses the celestial equator from north to south.
For Mitchell residents, that moment comes at 7:05 p.m. CDT on Sept. 22.
Day and Night Aren’t Exactly Equal
The word “equinox” comes from Latin words meaning “equal” and “night,” but Mitchell won’t experience exactly 12 hours of daylight and 12 hours of darkness.
The Earth’s atmosphere bends, or refracts, sunlight, allowing us to see the sun when it is technically just below the horizon. The National Weather Service explains that atmospheric refraction and the way sunrise and sunset are measured give us slightly more than 12 hours of daylight on the equinox.
Fall Can be a Good Time to Watch for the Northern Lights
South Dakotans hoping to see the aurora borealis may want to keep an eye on the northern sky around the equinox.
Geomagnetic activity tends to increase around the spring and fall equinoxes, improving the chances of aurora displays when solar conditions cooperate, according to NASA.
The First Day of Fall Changes
Fall doesn’t always begin Sept. 22. The timing varies slightly because Earth’s trip around the sun doesn’t line up perfectly with our 365-day calendar.
In 2026, however, Mitchell can mark the calendar for Tuesday, Sept. 22.