The first day of fall is Sept. 22, 2025. The word equinox comes from the Latin for “equal nights.” On Sept. 22, the fall, or autumnal, equinox occurs when the sun is directly above the equator, and day and night are each about 12 hours long in the Northern Hemisphere.
The spring and fall equinoxes are the only days the sun crosses the celestial equator going southward; it rises exactly due east and sets exactly due west. From that point on, temperatures begin to drop and days become shorter than nights. It also marks the beginning of the season for vibrant fall colors.
The four seasons are determined by changing sunlight (not heat) based on Earth’s orbit around the sun and the tilt of its axis.
