The Harvest Moon is the full Moon that occurs closest to the Autumnal Equinox. It often occurs in September, but can also occur in October. An erroneous popular belief is that the Harvest Moon is the brightest Moon of the year, so bright that you can harvest crops by its Moon light. In truth, you can harvest crops by the light of any full Moon. The reason the September / October Moon has this reputation is because it occurs during harvest.