September 22, 2025: Autumn begins in the northern hemisphere at 1:19 p.m. CDT, when the sun crosses the celestial equator heading south. Learn how the equinox marks the change of seasons and the balance of daylight and darkness.
by Jeffrey L. Hunt
Chicago, Illinois: Sunrise, 6:39 a.m. CDT; Sunset, 6:47 p.m. CDT. Times are calculated by the US Naval Observatory’s MICA computer program. Check local sources for sunrise and sunset times.
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Autumn Begins
Autumn begins in the northern hemisphere when the sun reaches the celestial coordinates where it crosses the equator moving southward, at 1:19 p.m. Central Time.
The sky can be visualized as an immense sphere, with the horizon limiting our view to one half. For simplicity, this celestial sphere is described as turning, representing Earth’s rotation. Features such as the celestial poles and celestial equator are projections of Earth’s poles and equator onto the sky.
Earth’s revolution around the sun traces the ecliptic, a circle inclined 23.5° to the celestial equator. The equinoxes occur where the ecliptic intersects the celestial equator.
When the sun is north of the celestial equator, its rays favor the northern hemisphere, bringing warmer seasons. When it is south of the equator, the southern hemisphere experiences its warmer weather.
This autumn lasts 89 days, 21 hours, and 44 minutes, ending with the winter solstice. Its midpoint occurs on November 6th at 11:30 p.m. Central Time.
Darkness and Daylight
At Chicago’s latitude, darkness is longer than daylight beginning October 31st and lasting through February 10, 2026. Daylight is when the sun is above the horizon, while night includes twilight and complete darkness. During this 103-day interval, the darkness portion of night exceeds daylight.
This duration varies by latitude: Cocoa, Florida – 59 days; Tucson, Arizona – 80 days; Fayette, Missouri – 98 days; Seattle, Washington – 112 days; Juneau, Alaska – 120 days.
For planetary positions, see yesterday’s article. This morning, Venus has stepped farther from Regulus, while the other planets are nearly in the same places as yesterday.
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