the.com/harvest moon

means The full moon nearest the autumn equinox, which rises around sunset for several nights in a row, giving farmers extra light to bring in the last crops.

from From Old English hærfest, meaning 'autumn' or 'the harvest season' itself, long before the word narrowed to just mean the act of reaping — so a 'harvest moon' is literally the 'autumn moon.' The name stuck to this particular full moon because of real orbital geometry: near the equinox, the moon's path along the horizon is shallow, so it rises only slightly later each night instead of the usual 50 minutes — giving farmers several dusk-lit evenings in a row to finish the harvest before frost. No folklore needed; the sky actually cooperates.