Blue moon
[5] The practice of designating the second full moon in a month as "blue" originated with amateur astronomer James Hugh Pruett in 1946.
A 1528 satire, Rede Me and Be Nott Wrothe, contained the lines, “Yf they saye the mone is belewe / We must beleve that it is true.”[13] The intended sense was of an absurd belief, like the moon being made of cheese.
The OED cites Pierce Egan’s Real Life in London (1821) as the earliest known occurrence of “blue moon” in the metaphorical sense of a long time.
[2] The use of blue moon to mean a specific calendrical event dates from 1937, when the Maine Farmers' Almanac used the term in a slightly different sense from the one now in common use.
“A blue moon in the original Maine Farmers' Almanac sense can only occur in the months of February, May, August, and November.
"[2] This later sense gained currency from its use in a United States radio programme, StarDate on January 31, 1980 and in a question in the Trivial Pursuit game in 1986.
[10] According to the Encyclopaedia Britannica, scattering is the cause of “that epitome of rare occurrences, the blue Moon (seen when forest fires produce clouds composed of small droplets of organic compounds).” [9] A Royal Society report on the 1883 Krakatoa eruption[27] gave a detailed account of “blue, green, and other coloured appearances of the sun and moon” seen in many places for months afterwards.[27]: xiii .
The report mentioned that in February 1884 an observer in central America saw the crescent moon as “a magnificent emerald-green” while its ashen part was “pale green”.
Winds carried the smoke eastward and southward with unusual speed, and the conditions of the fire produced large quantities of oily droplets of just the right size (about 1 micrometre in diameter) to scatter red and yellow light.
The Antarctic diary of Robert Falcon Scott for July 11, 1911 mentioned "the air thick with snow, and the moon a vague blue".
[31] The key to a blue moon is having many particles slightly wider than the wavelength of red light (0.7 micrometer)—and no other sizes present.
Ash and dust clouds thrown into the atmosphere by fires and storms usually contain a mixture of particles with a wide range of sizes, with most smaller than 1 micrometer, and they tend to scatter blue light.
There is no evidence of “blue moon” having been used as a specific calendrical term before 1937, and it was possibly invented by the magazine’s editor, Henry Porter Trefethen (1887-1957).
[2] As a term for the second full moon in a calendar month it began to be widely known in the U.S. in the mid-1980s and became internationally known in the late 1990s when calendrical matters were of special interest given the approaching millennium.
It created a misapprehension that the calendrical meaning of “blue moon” had preceded the metaphorical one, and inspired various folk etymologies, e.g. the “betrayer” speculation mentioned earlier, or that it came from a printing convention in calendars or a saying in Czech.
It is said that when a person sees a blue moon and makes a wish, he will be granted a second chance in things.”[34] In 1999 folklorist Philip Hiscock presented a timeline for the calendrical term.
Six years later, Laurence J. Lafleur (1907-66) quoted the almanac in the U.S. magazine Sky & Telescope (July 1943, page 17) in answer to a reader’s question about the meaning of “blue moon”.
In 1980 the term was used (with Pruett’s definition) in a U.S. radio program, Star Date, and in 1985 it appeared in a U.S. children’s book, The Kids' World Almanac of Records and Facts (“What is a blue moon?
It is a rare occurrence.”)[36] In 1986 it was included as a question in Trivial Pursuit (likely taken from the children’s book), and in 1988 a forthcoming blue moon received widespread press coverage.
“Seasonal Moon names are assigned near the spring equinox in accordance with the ecclesiastical rules for determining the dates of Easter and Lent.
[44] The fourth column shows blue moon dates that were actually printed in the Maine Farmers’ Almanac, as found by Olson, Fienberg and Sinnott in 1999.
