Autumn Equinox 2024 Southern Hemisphere Calendar. When does the autumn equinox happen? Autumn equinox 2024 (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.

Due to the differences between the calendar year and the tropical year, there’s no exact date of the autumn equinox. Autumn equinox 2024 (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.