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“Discover how lunar events shape timeless sayings” ~Crystal Wind

Exclusive Publication | Crystal Wind News Service |

There is no shortage of folklore surrounding the moon. Popular belief has long held that full moons drive people to strange behavior — higher emergency room visits, more erratic decisions, wilder parties. Most serious scientific studies, though, have consistently failed to find any real evidence for it. The moon, it seems, gets credit for a lot of things it didn't do.

Of all the moon-related folklore circulating today, few terms have a stranger or more tangled history than "blue moon." The names given to moons at particular times of year have existed for centuries, and almanacs have long catalogued twelve of them — one per month. The Harvest Moon is the most famous, rising near the fall equinox and casting enough light over the fields to let farmworkers push on well into the night. The Hunter's Moon followed by analogy, and a handful of other almanac names carry that same faint smell of later invention. But the blue moon is different from all of them. It isn't tied to any season. It moves around. It is, in the old phrase, a movable feast.

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

Many people today will confidently explain that "according to folklore," a blue moon is the second full moon in a calendar month, and that this is where the phrase "once in a blue moon" comes from. That explanation sounds tidy. It also happens to be wrong — or at least, only partially right.

"Once in a blue moon" is genuinely old, stretching back well over a century and a half. But the specific definition of a blue moon as the second full moon in a calendar month is surprisingly recent, far younger than the phrase itself. The older meaning and the newer one have been running alongside each other for decades now, and neither has replaced the other.

It's also worth noting that two full moons in a single calendar month isn't actually that rare. Because the lunar cycle — roughly 29.53 days — is shorter than almost every calendar month, and because our calendar pays no attention whatsoever to moon phases, the overlap happens about seven times every nineteen years. That works out to roughly once every thirty-three months on average. According to the Old Farmer's Almanac, the most recent blue moon falls on May 31, 2026 — the second full moon of May, following the first on May 1. The next one after that won't arrive until December 31, 2028. Think of it a bit like being paid every second Friday and occasionally finding that a particular month contains three paydays instead of two.

The word "blue moon" itself has been in use for over four hundred years, and in that time its meaning has drifted considerably. At least six distinct meanings have attached themselves to the term at various points in history, and no fewer than four of them remain in circulation today. That makes any simple explanation of the phrase almost impossible.

The earliest recorded uses of "blue moon" treated it the way a later age might treat "when pigs fly." To say someone would argue that the moon was blue was to say they'd argue about anything, no matter how obviously absurd. This was the first meaning: the blue moon as an impossibility. From there, a second meaning followed naturally — that something would happen "when the moon turns blue" meant it would happen never. It sat comfortably alongside other expressions for the unthinkable, like waiting for the twelfth of never.

But of course the moon does occasionally appear blue — and that is the third meaning, the literal one. When the Indonesian volcano Krakatoa erupted in 1883, its ash turned sunsets green and the moon blue across much of the world for nearly two years. A late monsoon in India in 1927 produced similar effects. Forest fires in Alberta in 1951 sent smoke particles high enough into the atmosphere that observers across Newfoundland reported seeing a genuinely blue moon. As EarthSky notes, blue-colored moons are extremely rare today, typically associated with major wildfires or volcanic eruptions that push fine particles into the upper atmosphere. By the mid-nineteenth century it was clear that while visually blue moons were rare, they did happen — and so the fourth meaning emerged: "once in a blue moon," meaning infrequently, but not quite never. That is still the phrase's primary meaning today.

A fifth meaning arrived through music. At least six well-known songs have used "blue moon" as a symbol of loneliness and longing — in several of them, the moon obligingly turns to gold once the singer finds his love. Classic recordings by Elvis Presley and Bill Monroe both trade on this symbolism, and it has become deeply embedded in American popular culture.

The sixth and most recent meaning — the second full moon in a calendar month — has the most curious origin story of all. According to Wikipedia, the practice of designating the second full moon in a month as a "blue moon" is generally traced to amateur astronomer James Hugh Pruett, writing in a 1946 issue of Sky & Telescope. Research has since pushed the trail back a little further, to a 1943 "star quiz" in the same magazine, where the author attributed the term to a 19th-century Maine almanac. Despite extensive searching, no one has yet produced that Maine almanac. The term, used in this specific calendrical sense, seems to have been extraordinarily local — perhaps confined to a single region, or even a single family — before it surfaced in print.

What appears to have launched the term into mainstream consciousness was a combination of forces: a radio astronomy program in the late 1970s that used the blue moon terminology on air, a children's almanac published in 1985, and the board game Trivial Pursuit, which included a blue moon question in its 1986 "Genus II" edition. Then in May 1988, with two full moons falling in the same month, wire services picked up the story and fed it to newspapers, radio stations, and television newsrooms across North America. The term took off. What had been obscure, possibly invented, possibly borrowed from a single forgotten almanac, became common knowledge almost overnight.

There is something almost fitting about that. Folklore has always worked this way — terms and beliefs drift, get picked up, get set down, get misremembered, and eventually take root somewhere unexpected. The "blue moon" as the second full moon in a month is not ancient folklore, whatever some sources may claim. But it is real folklore. It was adopted, spread, repeated, and believed by millions of people. That's how these things happen.

"Once in a Blue Moon" — A Brief History of the Phrase

The earliest known appearance of the expression in print dates to 1528, in a pamphlet called Rede Me and Be Not Wroth:

Yf they say the mone is blewe,

We must believe that it is true.

Making allowances for pre-Elizabethan spelling, the meaning is clear enough: nobody actually believed the moon could be blue. "Once in a blue moon" meant never. As the Morris Dictionary of Word and Phrase Origins (William and Mary Morris, Harper & Row, 1977) notes, it was only as physical phenomena — dust storms, volcanic ash, ice crystals in the atmosphere — made it clear that the moon could on very rare occasions genuinely appear blue, that the phrase softened from "never" to something closer to W.S. Gilbert's famous line from H.M.S. Pinafore: "What, never? Well, hardly ever."

The following year after the 1528 pamphlet, another writer introduced the moon's rival absurdity — that it was made of green cheese. These two ideas ran in parallel for a time, both used as examples of things no reasonable person would believe. As Charles Earle Funk observed in A Hog on Ice and Other Curious Expressions (Harper, 1948), the "green cheese" reference was not about color but freshness — a newly pressed cheese resembles the full moon both in shape and pale color. The "blue" cheese, by contrast, suggested a moon gone moldy, metaphorically transferred to those rare, crystalline nights when the entire lunar surface is faintly visible even in a thin crescent. From these two competing sixteenth-century absurdities, our phrase "once in a blue moon" may have grown.

Today the phrase means exactly what it has meant for roughly 150 years: something that happens infrequently, irregularly, but not quite never. It is one of those idioms that has outlasted almost every explanation of where it came from.

Blue Moon Frequency

A major moon phase can occur twice within a single calendar month for a simple reason: the calendar no longer tracks the moon at all. The word "month" derives from "moon," but a modern calendar month — one-twelfth of a year — is longer than the average lunar cycle of 29.53 days. In any given century there are 1,200 calendar months, but on average 1,236.83 full moons. The difference — roughly 36.83 — is the average number of blue moons per century, or about one every 2.72 years.

According to timeanddate.com, the next monthly blue moon falls on May 31, 2026, with the next seasonal blue moon following on May 20, 2027. After the 2026 event, the next monthly blue moon won't arrive until December 31, 2028. Occasionally, years produce two blue moons rather than one — this happens when February, the shortest month, passes without a full moon at all, pushing the surplus into two other months of the same year.

The bottom line, as lunar researchers have noted, is that just under 3% of all full moons qualify as blue moons. Rare, but not impossibly so. Which is, when you think about it, exactly what the phrase has always meant.

"Folklore has always worked this way — terms and beliefs drift, get picked up, get set down, get misremembered, and eventually take root somewhere unexpected."

Disclaimer: The information in this article is presented for educational and informational purposes only. Views expressed are those of the contributing author and do not necessarily reflect the views of CrystalWind.ca, which makes no claims regarding the accuracy of any content herein.

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