Oh, I know. I just did some condensing for the sake of simplicity. BBIt's the third harvest festival, the first being of wheat at Lammas and the second at Equinox, still celebrated. Lammas, 1st August, is the cross-quarter day when daylight hours start to rapidly dwindle, Samhain, 1st November, is the cross-quarter day when that decline slows to a crawl, although technically it's more like 7th August to 5th November.
*northern hemisphere, ofc.