When will autumn 2026 begin astronomically?

The autumnal equinox, marking the start of autumn in the Northern Hemisphere, is set to occur on Wednesday, September 23, 2026. This astronomical event signals the end of summer and the onset of a new season characterized by gradually improving weather. As autumn approaches, temperatures will begin to decrease, and humidity levels will drop, leading to milder conditions as winter nears.

Derived from astronomical calculations, the 2026 seasons exhibit varying durations. Spring began on March 20, 2026, and lasted 92 days and 17 hours. Summer, in turn, commenced on June 21 and will persist for 93 days and 15 hours. Autumn, according to astronomical definitions, will commence on September 23 and last for 89 days and 20 hours. Winter will begin on December 21 and endure for 88 days and 23 hours.

The gradual transition to autumn is accompanied by a decrease in temperatures, particularly noticeable during the first half of September, where summer-like elements such as high temperatures and humidity may still prevail. The autumnal equinox, occurring when the sun's rays are nearly perpendicular to the equator, results in nearly equal day and night lengths worldwide.

Subsequent to this event, daylight hours in the Northern Hemisphere progressively decrease, while nighttime hours increase, contributing to the observable change in weather patterns as autumn unfolds.