Autumn Solstice 2025. The equinox and solstice define the transitions between the seasons of the astronomical calendar and are a key part of the earth's orbit around the sun. Autumn equinox 2025 (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.

Find out more about equinoxes and solstices. This point is on the celestial.