Overview

• Today, September 22, is the calendar start of autumn in 2025, with the equinox occurring at 20:19.
• Meteorological autumn began on September 1 and runs through November 30, a fixed three‑month span used for consistent climate statistics since the 19th century.
• Around the equinox, day and night are approximately equal, after which days grow shorter and nights longer until the winter solstice on December 21.
• Earth’s seasons arise from its roughly 23.5‑degree axial tilt, which changes the sun’s midday height and the length of daylight through the year.
• The astronomical date of autumn varies annually because it depends on the exact timing of the sun crossing the celestial equator.