This can refer to the season, or to a time of maturity. Here are some sentences.
The autumnal equinox is also known as the fall equinox and the September equinox. An example of a sentence using "autumnal equinox" is "This year's autumnal equinox falls on a full moon. "
i screwd my boy so hard his balls turned an autumnal color
As Jo woke up in autumn she said that it was an autumnal morning because she felt the chill.
Autumnal Rustic was created in 1788.
Autumnal Moth was created in 1794.
Autumnal was created on 2009-01-10.
September 22
Autumnal Equinox was 23. September in 1978
In 2011, the Autumnal Equinox begins on September 23rd.
Lines on an Autumnal Evening was created in 1793.
The "autumnal equinox" is a single point in time, not a period. In 2015, the autumnal equinox will happen at 08:20 (UT) on the 23rd September.
In the Northern hemisphere, daylight hours decrease after the autumnal equinox.