Autumnal And Vernal Equinoxes 2024. Autumnal equinox — is an astronomical phenomenon, when the sun in its visible motion along the ecliptic crosses the celestial equator. Earth’s tilt on its axis is what causes this northward shift of the.

In other words, on the day of the. Autumnal equinox — is an astronomical phenomenon, when the sun in its visible motion along the ecliptic crosses the celestial equator.