autumnal equinox

As Jupiter's northern hemisphere was passing through its autumnal equinox, they concluded they had landed exactly at the pole.

The summer had now passed, and the autumnal equinox was rapidly approaching.

The autumnal equinox day came round, and the monster ate nothing.

At the vernal and at the autumnal equinox I take a good meal, and that lasts me for half a year.

They call this autumnal equinox the beginning of the civil year, and the vernal equinox the beginning of the holy year.