Sabbat
The second harvest, and the youngest name on the Wheel — about fifty years old, and straightforward about it.
These are associations the community holds, not settled fact — the more a reading is shared, the bolder it sits.
The autumn equinox is the sun crossing the celestial equator southward, between 21 and 24 September and in practice almost always the 22nd or 23rd. Day and night come close to equal, and the balance is the part practitioners work with: what is stored, what is owed, what can be allowed to end tidily.
The name is the newest thing here, and there is no reason to be coy about it. Mabon was applied to the equinox in 1974 by the American writer Aidan Kelly, who took it from Mabon ap Modron — "son of mother" — a figure out of the medieval Welsh tale Culhwch and Olwen. No medieval source connects him to the equinox or to a harvest. It is a modern name given to a real observance because the Wheel wanted eight names and only had five with any history to them.
Mabon is where the romantic version of the Wheel is easiest to check and hardest to defend. Say instead: people have marked the equinox for a very long time, this label is about fifty years old, and the second harvest is no less real for it. Southern-hemisphere practitioners keep it at the March equinox.
Readings practitioners have offered, ordered by how many recognise them. Take what serves, leave the rest.
Carried forward
Culhwch and Olwen, in Lady Charlotte Guest’s Mabinogion (1849)
In the tale, Mabon is taken from his mother when three nights old and imprisoned somewhere nobody living can name. He is found only by asking a chain of ever older animals — the blackbird, the stag, the owl, the eagle, and at last the salmon, who has heard him crying. It is a story about asking older things for directions, which is at least a fair fit for the season.
Carried forward
Common in contemporary practice
Practitioners increasingly say "autumn equinox" and keep Mabon as a nickname, having learned where the word came from. Both are in use, and nobody sensible minds which you pick.
Credit what you carry. Much of this comes from living traditions, and some of it from traditions that are closed — held by particular peoples and not offered for general use. Where you know whose practice a reading came from, name them; where you don't, say that too.