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Autumn Begins as Sun Crosses the Equator at 2:19 p.m. ET

Despite the name, day and night are only nearly equal today because of how we measure sunlight and atmospheric refraction, with true equality arriving a few days later in many places.

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Overview

  • NASA and observatories place the equinox at Monday, Sept. 22, 2:19 p.m. ET (1:19 p.m. CDT; 7:20 p.m. BST), the precise instant the Sun’s center crosses Earth’s equatorial plane.
  • Astronomical autumn starts in the Northern Hemisphere as the region tilts away from the Sun, while spring begins in the Southern Hemisphere and daylight patterns reverse.
  • Exact 12-hour day and night typically occur later at the ‘equilux’—for example, several U.S. cities reach it around Friday, Sept. 26, due to solar disk size and atmospheric refraction.
  • Meteorological fall, used for climate tracking, began Sept. 1 and runs through Nov. 30, differing from the astronomy-based seasonal boundaries.
  • Geomagnetic activity often increases around the equinoxes, boosting Northern Lights odds, and upcoming clock changes include Oct. 26 in the UK and Nov. 2 in the U.S.