THE term “harvest moon,” originating in England, where the brilliant moon-light of several consecutive evenings aided the harvesting of crops, is the popular expression for the moon at its full in the month of September in northern latitudes. This phenomenon of early moon-rise is dependent upon the degree of retardation of the moon's rising, as affected by difference in latitude. As conditions in England are especially favorable, full moon-rise at harvest time therefore occurs earlier than in the lower latitudes of this country. Following out this law of retardation, it is a matter of course to look for a yet earlier rising of the “harvest moon” in the far north of the Scandinavian peninsula; and an extremely opposite condition in the corresponding latitudes of the Southern hemisphere, where the “harvest moon” (if it were possible to use the term in this region) would occur about the time of the vernal instead of the autumnal equinox. Variations in the retardation of the moon's rising (a retardation which averages about 51 minutes daily) are due to complex conditions. If the earth's axis were perpendicular to the plane of the ecliptic, and if the earth and moon revolved in circular orbits at uniform velocities around their respective centers of motion in that plane, the retardation would obviously be constant. But the earth's axis is inclined at an (Continued on page SO..)
This article was originally published with the title "The Harvest Moon"