The astronomical autumn equinox for 2026 will occur in central Mexico on Tuesday, September 22, at 18:05 local time. ^[1] The September 2026 Harvest Moon is defined astronomically as the full moon occurring closest to the autumnal equinox in the Northern Hemisphere. ^[2] The same astronomical event is registered internationally on September 23 at 00:05 hours in Universal Time, but the six-hour time difference causes it to occur during the afternoon of the previous day in Mexican territory. ^[3] Historically, before modern electric lighting, farmers in the Northern Hemisphere relied on the Harvest Moon because the interval between sunset and moonrise was shorter than usual. ^[4] The bright early-rising light of the Harvest Moon allowed farmers to extend their work hours in the fields to complete harvests before the arrival of cold autumn weather. ^[5] When the Harvest Moon first rises near the eastern horizon, it often appears larger and reddish-orange compared to when it is higher in the sky. ^[6] After the equinox, days will begin to shorten and nights will become progressively longer until the winter solstice of December 21, 2026. ^[7]