once in a blue moon?

Question

what does it mean by that

Answer 1

"Once in a blue moon" means *exceedingly* rare (in fact, something you might NEVER see!)... much rare than the "second full moon in a month" explanation suggests.

In fact. . . sorry to all those who have accepted the notion, but the "second full moon in a month" explanation is incorrect in two respects.

First, the astronomical use of the expression "blue moon" is very recent and is NOT the source of the old expression "once in a blue moon" , which appeared in print as early as 1528 -- and seems to have more to do with a LITERAL "blue moon" (a rare occurrence, at best)

Second, the "second full moon" explanation was itself based on a misunderstanding of the astronomical use of the term!

-------------------------

The Astronomical Mistake

This "second full moon" explanation, popularized by the board game "Trivial Pursuit" is actually based on a mistake in a 1946 article in Sky & Telescope magazine.

In 1999 the magazine printed two articles on the subject by way of retraction

A) explaining the REAL meaning of the astronomical expression (which is somewhat more complicated than the catchy "second full moon" idea),
"What's a Blue Moon?"
explains the correct astronomical usge -- when a season contained four full moons, the third was known as a "blue moon" -- and how the 1946 mistake came about
http://skytonight.com/observing/objects/moon/3304131.html?page=1&c=y

and
B) tracing just how the mistake was made and has spread into popular lore (via radio, Trivial Pursuit and newspaper articles)
"Once in a Blue Moon:Fact and fantasy about blue Moons" by Philip Hiscock
(opening snip)
"According to old folklore," some people say, the second full Moon in a calendar month is called a "blue Moon." They go on to explain that this is the origin of the expression "once in a blue Moon." But it isn't true! The term "blue Moon" has been around a long time, well over 400 years, but its calendrical meaning has become widespread only in the last 20 years."
http://skytonight.com/observing/objects/moon/3305141.html

Compare
http://www.wilsonsalmanac.com/bluemoon.html

------------------------

The REAL Origins

But all the astronomical uses (even the correct one!) are very recent, and have nothing to do with the origins of the expression "Once in a blue moon"

An sample explanation of the meaning
E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
Blue Moon: Once in a blue moon. Very rarely indeed.
On December 10th, 1883, we had a “blue moon.” The winter was unusually mild.
http://www.bartleby.com/81/2105.html

Here is an explanation of just what the older "blue moon" of the expresion was:

"Once in a Blue Moon" is a phrase that refers to something that in all likelihood will never happen at all or only far off in the future. . . . The expression itself derives from the extremely rare, actually blue-tinged Moon caused by atmospheric layers of forest-fire smoke or volcanic dust at just the right height and visual angle, a rare occurrence."
http://www.ipl.org/div/farq/bluemoonFARQ.html

(Also note that the original "blue moon" need not be a FULL moon.)


See also the summary & links at:
http://en.wikipedia.org/wiki/Blue_moon

Answer 2

A blue moon is the full moon of a declension greater than +19 degrees with a maximum of +29 degrees to the northern hemisphere. In the middle of the night the moon appears to be almost directly overhead, which gives the night sky it`s bluish tint. This occurred last week (Nov 22-23),so for the next ,consult an astronomical almanac.

Answer 3

once in a blue moon means that something doesn't usually happen. Like you might say to someone I eat ice cream once in a blue moon. It's just saying you don't eat ice cream very often.

Answer 4

A "blue moon" is a fairly rare event. Whenever there are two full moons in the same month, the second one is called a "blue moon".

Answer 5

If something happens "once in a blue moon" it means that it doesn't happen very often.

Answer 6

It just means that it's very unlikely to happen or it rarely happens. A blue moon is rare. (I think it's when you have two full moons in a month.)

Answer 7

Sometimes there will be two full moons within the same month. The second one is the blue one.

Answer 8

The 'blue moon' expression itself is old and dates back to mediaeval England, There are rare examples of the moon actually appearing blue, after volcanic eruptions or unusual weather conditions.

Answer 9

It means something that doesn't happen very often. A blue moon is when a full moon happens twice in one month. (which doesn't happen very often)

Answer 10

Like the second full moon in the same month...rarely happens.