What is a "blue moon," and where does the phrase "once in a blue moon" come from?

                         Folklore of the "Blue Moon"

                               Philip Hiscock
                       MUN Folklore & Language Archive
                     Memorial University of Newfoundland

Depending on where you lived, 1993 had a "blue moon" in either August or
September. If you were east of a line running down the Atlantic Ocean,
the blue moon fell in September; west of that line, the blue month was
August.

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.

At least once during August or September this year [1993], you probably
heard through the media about the "blue moon." 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. In 1999 there
will even be two "blue" moons. 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 this
year--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.

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                                  SIDEBARS

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                            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.

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                             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

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                       Remaining "Blue Moons" in the
                         20th Century (times in UT)

                             1996 July 30 10:35
                            1999 January 31 16:06
                             1999 March 31 22:49

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                           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

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An earlier version of this article appeared in The Plains Planetarian,
Fall 1993. The article was published in its present form in the
Planetarian, December 1993. Copyright 1993 International Planetarium
Society.

-- Philip Hiscock, MUN Folklore & Language Archive

[ Editor: the source also points to David Harper's Blue Moon page for a
Blue Moon Calculator; no address is given. ]