Fall Equinox 2025 Dates And Times. Autumn equinox 2025 (beginning of astronomical autumn) on the day of the autumn (september) equinox, the sun, moving along the ecliptic, crosses the celestial equator, moving from the northern hemisphere to the southern. The autumn or fall equinox signals the end of summer on the astronomical calendar.
When do the four seasons start in 2025—for spring, summer, fall, and winter? The autumn or fall equinox signals the end of summer on the astronomical calendar.