harvest moon, full moon occurring nearest to the autumnal equinox, about Sept. 23. During harvest moon the retardation (later rising each night) of the moon is at a minimum because of the relation of the moon's path to the horizon. On several nights in succession the moonrise is at nearly the same time, and there is full moonlight almost from sunset to sunrise if the sky is unclouded.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.
More on harvest moon from Fact Monster:
See more Encyclopedia articles on: Astronomy: General