When Is September Equinox 2025
When Is September Equinox 2025. In 2025 the autumnal equinox will occur on 22 september at 12.44pm gmt (1.44pm bst). In 2025, the autumnal (fall) equinox arrives on sunday, september 22, marking the official first day of fall.
An equinox is one of two days in the year when the sun crosses the equator and day and night become equal in length. It also lists astronomical sunrise and sunset timings on autumnal.