The moon near the full at the time of harvest in England, or about the autumnal equinox, when, by reason of the small angle of the ecliptic and moon’s orbit with the horizon, it rises nearly at the same hour for several days. — Webster, 1882
The harvest moon is so called, quaintly says Ferguson, the Scotch astronomer, because “the farmers of the old country gratefully ascribe the early rising of the full moon at this time of the year to the goodness of God, not doubting that He has ordered it so on purpose to give them an immediate supply of moonlight after sunset for their greater convenience in reaping the fruits of the earth.” -Redwood (Minnesota) Gazette, 1878
In Farmer Boy, the harvest moon casts a glow over the fields at night at the time of gathering late fall crops for storage. The extra bit of light was useful at the busy time of harvest. The Wilders pick apples, gather the garden beets, turnips and parsnips, and pull onions and pepppers. Almanzo Wilder carefully cuts his milk-fed pumpkin from the vine. (See Chapter 20, “Late Harvest”)
In the United States, the harvest moon is the full moon closest to the autumnal equinox, the time when the tilt of the earth (with respect to the sun) is zero degrees, so night and day are equal in length. The autumnal equinox falls on September 22 or 23 each year in the Northern Hemisphere. In 1866, when Almanzo Wilder was nine years old, the autumnal equinox was on Sunday, September 23rd. There was a full moon the following day, on September 24th, so this was the harvest moon date for the year 1866.
The harvest moon doesn’t always fall in September. It can be anywhere from two weeks before to two weeks after the autumnal equinox, meaning it can be on a day between September 8 and October 7, depending on the year. There are many perpetual moon calendars online if you wish to find the date of the harvest moon in a particular year. HERE is NASA’s moon calendar for the years 1801-1900; the site has pages for other centuries as well.
For the year 2015, when this LIW A-Z entry was last edited, the autumnal equinox comes on September 28 in the Northern Hemisphere.
Note: the harvest moon painting used for the navigation button that brought you here is Samuel Palmer’s “The Harvest Moon” (1833). The image above is Helen Allingham’s “The Harvest Moon,” painted in 1879.
harvest moon (FB 20), see also equinoctial storm