Autumn Equinox 2024. 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 2024 (beginning of astronomical autumn) on the day of the autumn (september) equinox, the sun, moving along the ecliptic, crosses the celestial equator,.
According to the astronomical autumn, the autumn equinox will signal the start of the season and begin on the 22nd of september 2024. In 2024, the autumnal (fall) equinox arrives on sunday, september 22, marking the official first day of fall.