Fall Equinox 2025 Dates Usa Calendar. 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. Summer begins with the summer solstice, friday, june 20, 2025, 10:42 p.m.

The other three forty day periods are: When in 2025 is september equinox?