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September 2003: The Harvest Moon


The Harvest Moon refers to the Full Moon that comes closest to the autumnal equinox, or the first day of autumn. Depending on the year, the Harvest Moon can fall anywhere from two weeks before to two weeks after the equinox, which arrives annually on or near September 23. This year, the Harvest Moon reaches full phase on September 10.

It's almost as though two Harvest Moons are in the works this year, with the equinox falling nearly halfway between the September and October Full Moons. The Hunter's Moon, the Full Moon following the Harvest Moon, exhibits the Harvest Moon's characterisitics, but usually to a lesser degree. This year, the two perform as costars.

Before the advent of artificial lighting, our ancestors were acutely aware of the daylight hours waning more rapidly around the autumn equinox (when the Sun rises due east and sets due west) than at any other time of year. But back then, people also understood lunar behavior, harvesting by the light of the Moon.

It was once common knowledge that at the vicinity of Full Moon, the Moon rises around sunset, shines all night long and sets around sunrise. Note for yourself on the night of September 9-10 that the Moon lights up the night sky from dusk till dawn.

After Full Moon, the Moon rises on the average of fifty minutes later with each passing night. Farmers in olden times knew, however, that this lapse of time between successive moonrises shrinks most dramatically near the fall equinox, ushering in a glorious parade of moonlit nights. With only twilight intervening between sunset and moonrise for nights on end, folks could gather their crops from under the lantern of the Harvest Moon.

The Harvest Moon is really a phenomenon of far northern (or southern) latitudes. At the Earth's equator, there is no Harvest Moon; and at the tropics, there's not enough of one to say so. From the middle latitudes of the continental United States, the Moon rises some twenty-five minutes later for several days in succession; but in Anchorage, Alaska, moonrise beams at the same time every day for a week, showcasing a bona fide Harvest Moon!

copyright 2003 by Bruce McClure

Another September Feature: Equinox Geometry