Equinox September 2025. The september equinox is one of four days with solar events (two equinoxes and two solstices) throughout the year that mark the beginning of a new season. At the september equinox, the sun is moving from north to south as it crosses above the equator.

The september equinox is one of four days with solar events (two equinoxes and two solstices) throughout the year that mark the beginning of a new season. This is also the first day of fall (autumnal equinox) in the northern hemisphere and the first day of spring (vernal equinox) in the.