The Autumnal Equinox in 2025 will occur on September 22 at 2:19 p.m. EDT, signaling the official start of fall in the Northern Hemisphere from an astronomical perspective. This event marks the moment when the Sun crosses the celestial equator, resulting in nearly equal lengths of day and night. While meteorological fall, defined by consistent temperature patterns, begins earlier, the autumnal equinox is the traditional marker of the seasonal transition.