Fall Equinox 2025. The dates of autumnal equinox / fall for the next 10 years: The autumnal equinox, also known as the september equinox in the northern hemisphere, begins on the day when the sun appears to cross the celestial equator and heads southward.

An equinox is one of two days in the year when the sun crosses the equator and day and night become equal in length. 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.