Depending on the calendar you're using, the autumnal equinox is on September 22 or 23rd this year. It depends on where you live in the world. Like it's spring counterpart, it is a day when the light and darkness are the same length. From here on in the days grow shorter.
It is also called Mabon, a pagan holiday which celebrates the harvest and pays homage to the coming darkness of the days ahead.
The weather has turned and the hillsides are beginning to be dotted with orange, red and yellow as the trees change color. The night are getting longer. It's a time of change, of celebration. Eat, drink and celebrate with family and friends. Enjoy the fruits of the harvest and look ahead to the coming months!