The full Moon closest to the autumnal equinox (September 23), when the Moon rises around the time of sunset for several nights in succession. This is because the ecliptic, and hence the Moon's orbit, is then at its minimum angle to the horizon at the time of moonrise in mid- or high northern latitudes. The harvest Moon is so named because its light in the evening was of help to workers at harvest time. See also retardation.
Subjects: Astronomy and Astrophysics.