There is a lot of folklore about the moon. Modern folklore has it that full moons make for better parties and higher booking rates at mental hospitals, but all the serious studies I've read deny the relationship.

The most interesting bit of modern folklore from my point of view as a student of language and folklore is the sudden popularity of the term "blue moon." Names of moons at certain times of the year have been around a long time, and almanacs are especially wont to list twelve of them. The Harvest Moon is the best known of these, lighting up the fields sometime after the fall equinox, enabling work to continue late into the night. 

Of course folklorists know that the traditional belief is widespread that certain crops harvested by the light of the moon, or alternatively in the waning of the moon, keep better than those cut at other times. The full Harvest Moon was a signal, to those who would listen, that it was time to start the last work of the year in the fields. The late fall Hunter's Moon was invented by analogy with the Harvest Moon, and some of the other almanac moon names have the same ring of later invention.

Blue Moon is different from the monthly or seasonal moon names as it isn't restricted to a time of year. It is a movable feast.

People have been saying that "according to folklore" the second moon in a calendar month is a "blue moon." So, they say, this is the origin of the phrase "once in a blue moon." Don't believe them! "Once in a blue moon" is old, about 150 years old, but the two-full-moons-in-a-month meaning of "blue moon" is a lot younger than that. The older meaning may be wishy-washy and the newer one solid and technical, but don't let anyone tell you they have replaced one with the other.

It's not rare to see two full moons in a month. Because the moon and our calendar are not in sync and all the months but February are longer than the moon's synodical cycle, it happens about seven times in every nineteen years. That's every thirty-three months on average. Months have different lengths, so the phenomenon moves around a bit. If you think about it, it's a little like getting paid every second Friday and finding that some months you get paid three times instead of twice.

Meaning is a slippery substance. The phrase "blue moon" has been around a long time, well over 400 years, but during that time its meaning has shifted. I have counted six different meanings which have been carried by the term, and at least four of them are still current today. That makes discussion of the term a little complicated.

The earliest references to a blue moon are in a phrase remarkably like early references to the moon's "green cheese." Both phrases were used as examples of obvious absurdities about which there could be no argument. Four hundred years ago, if someone said, "He would argue the moon was blue," the average sixteenth century man would take it the way we understand, "He'd argue that black is white." This understanding of a blue moon being absurd (the first meaning) led eventually to a second meaning, that of "never." To say that something would happen when the moon turned blue was like saying that it would happen on Tib's Eve (at least before Tib got a day near Christmas assigned to her). Or that it would be on the Twelfth of Never.

But of course we all know there are examples of the moon actually turning blue; that's the third meaning--the moon visually appearing blue. When the Indonesian volcano Krakatoa exploded in 1883, its dust turned sunsets green and the moon blue all around the world for the best part of two years. In 1927 a late monsoon in India set up conditions for a blue moon. And the moon here in Newfoundland was turned blue in 1951 when huge forest fires in Alberta threw smoke particles up into the sky. Even by the mid-nineteenth century it was clear that although visually blue moons were rare, they did happen from time to time. So the phrase "once in a blue moon" came about. It meant then exactly what it means today--that an event was fairly infrequent, but not quite regular enough to pinpoint. That's meaning number four, and today it is still the main one.

I know of six songs which use "blue moon" as a symbol of sadness and loneliness. In half of them the poor crooner's moon turns to gold when he gets his love at the end of the song. That's meaning number five: check your old Elvis Presley or Bill Monroe records for more information.

Finally, in the 1980s, came the most recent meaning of blue moon--the second full moon in a month. I first became aware of the new meaning of the term in late May, 1988, when it seemed that all the radio stations and newspapers were carrying an item on this interesting bit of "old folklore." At the MUN Folklore & Language Archive we get calls from all over, from people wondering about bits of folklore, and in that month I got calls about blue moons. You see there were two full moons that month.

There have been just a few double moon months since then, and 1993 was peculiar because the "blue moon" fell in either August or September. It fell in different months depending on where you live because the full moon was so close to midnight on the night of August 31st-September 1st. Some places got it before local midnight; others after. If your local full moon was before your local midnight, then your blue month was August; and if it fell after midnight, your blue month was September.

Back in 1988 I searched high and low for a reference to the term having this meaning, or for any other term used to describe two moons in a single calendar month. But it was in vain. There seemed to be just no history to this term. I uncovered information on the other meanings of "blue moon." But not this blue moon, meaning number six.

In December 1990, with a new "blue moon" coming on, I started getting calls again and I searched harder this time. I had already exhausted all the usual sources of historical and astronomical dictionaries, indexes of proverbial sayings and the like. A brand new edition of the huge Oxford English Dictionary had come out in the meantime, but even that seemed to have nothing on this new usage. A new tack was called for.

Almost every day I use computer networks to contact other folklorists around the world, so I started with them. But no one could give me a use of the term earlier than the 1988 wire stories. I then turned to other computer networks, for scientists and especially astronomers. Still no luck. "Blue moon" seemed to be a truly modern piece of folklore, masquerading as something old. Then my brother-in-law reminded me that the term was a question in one of the Trivial Pursuit boxes, the "Genus II edition," which was published in 1986. Trivial Pursuit is a fine company for scholars--they keep all their files and they can tell you the source of any bit of information in their games. Yes, they told me, that question came from a certain children's "Facts and Records" book, published in 1985. Where the authors of that book got it, no one seemed to know.

The term, used this two-full-moon way, must have been very, very local before the publication of the children's book, so local that it seemed never to have been written down by amateur or professional astronomers, or by the authors and newspapers which might have been searched by dictionary makers. It certainly was very rare. Perhaps, I thought, it was even made up by the authors of the children's book as a safeguard against plagiarism. This is sometimes done to be able to prove in a law court that a later work was stolen from your own -- how else would they have gotten something which you invented? Well, if this is what the authors did, they lost out because the term immediately entered the folklore of the modern world and it has become as living a meaning of the term "blue moon" as any of the earlier ones.

In late December 1990 I published my notes on the origin and development of the term, and posted it to an Internet computer network for folklorists. That month I also received Deborah Byrd's "Astronomy" article from that month in which she attributed "blue moon" to a note in a 1946 edition of "Sky & Telescope." Research eventually pushed that date back to 1943, and to an unnamed Maine almanac.

Deborah Byrd's late 1970's radio program, "Star Date," may in fact have been responsible for spreading the new (or reborn) term. During research for that program she ran across this 1943 "Sky & Telescope" "star quiz" which included a question about two full moons in a calendar month, the answer to which was "blue moon." The term clearly was not commonly known in 1943, and the author of the quiz, L. J. Lafleur, attributed it to a 19th century Maine almanac. I've searched for a Maine almanac with the term in it but to no avail--if any readers have such a thing, I'd be very grateful to receive a copy! On her "Star Date" show Byrd used the "blue moon" term; that probably started the ball rolling.

This is congruent with my original theory that the term was in local circulation (perhaps as local as a single Maine family -- the Lafleurs?) until it was made popular in the last decade or two by the media. Until the wire services took it in May 1988, those three media helpers were Deborah Byrd on the radio, the children's book (Margot McLoon-Basta and Alice Sigel, "Kids' World Almanac of Records and Facts," published in New York by World Almanac Publications, in 1985), and the board game Trivial Pursuit. The May 1988 double full moon really lifted the term off the ground by the interest of wire services feeding it to newspapers, radio stations and television newsrooms all over North America , and perhaps the world.

This new "blue moon" has a kind of technical meaning which most of the earlier ones lacked. Perhaps as a result, and although it competes with five other meanings, it will last a whole lot longer. "Old folklore" it is not, but real folklore it is.

Reference:

For a discussion of physical causes of a blue-appearing moon, with bibliography, and a list of blue moons from 1898 through 1999, see: "Once in a Blue Moon," Ronald Lane Reese and George T. Chang, in the Griffith Observer, March 1987, pp. 13-20.

once in a blue moon.

The first appearance in print of this expression goes back to well before the time of Shakespeare--to 1528, in fact. In a little item called Rede Me and Be Not Wroth appears:

Yf they say the mone is blewe
We must believe that it is true.

Making allowances for the fact that the pre-Elizabethians spelled differently from the way we do today, this makes the point that nobody really believed that the moon ever was blue. So once in a blue moon meant never. However, it appears that thanks to physical phenomena like dust storms, cloud banks and ice crystals in the atmosphere, the moon on very rare occasions may appear to be blue. So nowadays once in a blue moon translates best into W. S. Gilbert's famous line from H.M.S. Pinafore: "What, never? Well, hardly ever!"

--Morris Dictionary of Word and Phrase Origins, William and Mary Morris, Harper & Row, New York, 1977.

once in a blue moon

It means extremely infrequently, so rarely as to be almost tantamount to never. From literary evidence the unusual tinge to the face of the moon which led someone to call it a "blue moon" was not observed until after the middle of the last century; nevertheless it is highly probable that this phenomenon had been observed by mariners some centuries earlier, but, like many other notions and expressions long familiar to seafaring men, it did not come to the notice of writers for many, many years. But, with another thought in mind, as long ago as 1528 a rimester published these lines:

Yf they saye the mone is belewe,
We must believe that it is true.

Then the next year "green cheese" entered the picture in the lines of another writer: "They woulde make men beleue ... that ye Moone is made of grene cheese."

Apparently, then, there were two schools of thought back in the early sixteenth century--one maintaining that "ye Moone" was made of "grene" cheese, and the other stoutly affirming that it was "belewe." Actually these ancient humorists were just punsters with a taste for metaphor; for by "green cheese," it was not the color but the freshness that was referred to--the moon, when full and just rising, resembling both in color and shape a newly pressed cheese. By "blue cheese" the ancient reference was to a cheese that had become blue with mold, metaphorically transferred, probably, to the comparatively rare appearance of the moon on unusually clear nights when the entire surface of the moon is visible although no more than a thin edge is illuminated. Thus, our phrase "once in a blue moon" may actually date back to the sixteenth-century saying that "the mone is belewe."

--A Hog on Ice and Other Curious Expressions,
Charles Earle Funk, Harper, New York, 1948 

"Blue Moons" in the early 21st Century (times in UT)

• January 31, 2018
• March 31, 2018
• October 31, 2020
• August 22, 2021 (third Full Moon in a season with four Full Moons)
• August 30, 2023
• December 4, 2025
• May 31, 2026
• December 31, 2028
• September 31, 2031
• July 31, 2034
• January 31, 2037
• March 31, 2037
• October 31, 2039

Frequency of Blue Moons

A major Moon phase can happen twice within a calendar month for the simple reason that our calendar no longer pays any attention to Moon phases (even though the word "month" derives from "Moon"). What we call a month, namely 1/12 of a year, is longer than the averge length of time from a given Moon phase (say, Full) to the next recurrence of the same phase, which is 29.53059 days. There are 1200 calendar months in a century. In the same century, there are, on the average, 1236.83 Full Moons. The difference is the average number of Blue Moons in a century: 36.83, or an average of one per 2.72 years. Actually, about one year each 19 has two Blue Moons, because its shortest month, February, has no Full Moon at all; for the Eastern Time Zone, the complete list of such years from 1951 through 2050 is 1961, 1980, 1999, 2018, and 2037. Between such years, Blue Moons happen at intervals like 2 years and 7, 8, 9, or 10 months. the bottom line of all this complexity: just under 3% of all Full Moons are Blue Moons.

--Michigan Spacelog, July 1985, Jim Loudon
University of Michigan, Ann Arbor

For additional interesting information on Blue Moons and a Blue Moon Calculator, please see David Harper's Blue Moon page.

Blue moon calculater here!

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