Autumnal Equinox... occurs at the beginning of the fall season (when the tilt of the Earth's axis is again perpendicular to the Sun - but 180 degrees in reverse from the vernal equinox).
(Autumnal Equinox; occurs; T:at the beginning of the fall season) (the tilt of the Earth's axis; is; T:again; perpendicular to the Sun)
Autumnal Equinox the tilt of the Earth's axis
occurs is
T:at the beginning of the fall season
T:again perpendicular to the Sun