What Is The First Day Of Autumn In 2025. Autumnal equinox marks the end of summer and the beginning of fall. The seasons are defined as spring (march, april, may), summer (june, july, august),.
The first day of fall this year, also known as the autumnal equinox is sunday, sept. In 2025, the autumnal (fall) equinox arrives on sunday, september 22, marking the official first day of fall.
