Technically, an equinox is an astronomical point and, due to the fact that the earth wobbles on its axis slightly (rather like a top that's slowing down), the date may vary by a few days depending on the year. The autumnal equinox occurs when the sun crosses the equator on it's apparent journey southward, and we experience a day and a night that are of equal duration. Up until Harvest Home, the hours of daylight have been greater than the hours from dusk to dawn. But from now on, the reverse holds true. Astrologers know this as the date on which the sun enters the sign of Libra, the Balance (an appropriate symbol of a balanced day and night).
However, since most European peasants were not accomplished at calculating the exact date of the equinox, they celebrated the event on a fixed calendar date, September 25th, a holiday the medieval Church Christianized under the name of 'Michaelmas', the feast of the Archangel Michael. (One wonders if, at some point, the R.C. Church contemplated assigning the four quarter days of the year to the four Archangels, just as they assigned the four cross-quarter days to the four gospel-writers. Further evidence for this may be seen in the fact that there was a brief flirtation with calling the Vernal Equinox 'Gabrielmas', ostensibly to commemorate the angel Gabriel's announcement to Mary on Lady Day.)
The September 25th festivities actually begin on the previous sundown (our September 24th). Although our Pagan ancestors probably celebrated Harvest Home on September 25th, modern Witches and Pagans, with their desk-top computers for making finer calculations, seem to prefer the actual equinox point, beginning the celebration on its eve.
Mythically, it is the time of the year when night conquers day.
Incidentally, annual mock sacrifices of a large wicker-work figure (representing the vegetation spirit) may have been the origin of the misconception that Druids made human sacrifices. This charge was first made by Julius Caesar (who may not have had the most unbiased of motives), and has been re-stated many times since. However, as has often been pointed out, the only historians besides Caesar who make this accusation are those who have read Caesar. And in fact, upon reading Caesar's 'Gallic Wars' closely, one discovers that Caesar never claims to have actually witnessed such a sacrifice. Nor does he claim to have talked to anyone else who did. In fact, there is not one single eyewitness account of a human sacrifice performed by Druids in all of history!
Nor is there any archeological evidence to support the charge. If, for example, human sacrifices had been performed at the same ritual sites year after year, there would be physical traces. Yet there is not a scrap. Nor is there any native tradition or history which lends support. In fact, insular tradition seems to point in the opposite direction. The Druid's reverence for life was so strict that they refused to lift a sword to defend themselves when massacred by Roman soldiers on the Isle of Mona. Irish brehon laws forbade a Druid to touch a weapon, and any soul rash enough to unsheathe a sword in the presence of a Druid would be executed for such an outrage!
In the rhythm of the year, Harvest Home marks a time of rest after hard work. The crops are gathered in, and winter is still a month and a half away! Although the nights are getting cooler, the days are still warm, and there is something magical in the sunlight, for it seems silvery and indirect. As we pursue our gentle hobbies of making corn dollies (those tiny vegetation spirits) and wheat weaving, our attention is suddenly arrested by the sound of baying from the skies (the 'Hounds of Annwn' passing?), as lines of geese cut silhouettes across a harvest moon. And we move closer to the hearth, the longer evening hours giving us time to catch up on our reading, munching on popcorn balls and caramel apples and sipping home-brewed mead or ale. What a wonderful time Harvest Home is! And how lucky we are to live in a part of the country where the season's changes are so dramatic and majestic!
I can not remember where I obtained these articles many many years ago. In my youth I was never good about noting where I found things when searching online... Also, these articles has been changed in someways to depict it closer to how I perceive this Sabbat. I did not originally create these peices and I do not claim them to be mine, however over the years I have altered them, if you know of the original source, I'd be more than happy to link to and cite them.