What is the origin of the phrase "Once in a blue moon"?

Answer 1

A "blue moon" is the second full moon in one month. Since most of the time we have only one full moon a month, the blue moon is very rare. Because a blue moon is very rare, "once in a blue moon" has come to mean an activity that rarely occurs.

Answer 2

There are two possible origins of this phrase:-

The phrase 'once in a blue Moon' is a familiar one meaning once in a very long interval of time. The phrase goes back to at least 1824 when an explanation of its meaning appears as a footnote attached to its use. It is not absolutely clear what is the origin of this phrase but the rare blue colouring of the moon is the most likely.

1. Two full moons in One Tropical Year
The use of the phrase 'blue Moon' when there are two Full Moons in one calendar month appears to be spreading. There is no known knowledge of the origin of this usage but it appears that it has been 'back-derived' from the phrase denoting rarity with a rather misconceived idea that it is an uncommon thing for there to be two Full Moons in any one month.

For example, between 1984 and 2000 there were two full moons in the following months:-
Jul 1985
May 1988
Dec 1990
Sep 1993
Jul 1996
Jan 1999
Mar 1999

It can be seen that in 1999 there were two such months with only February between them. It could well be said this is not rare enough a phenomenon to qualify for the normal use of the phrase 'once in a blue Moon'.

A blue Moon, by folklore definition is said to be the second Full Moon of the month. However, researchers at Southwest Texas State University have been using historical documents to prove that a blue Moon was really a term that was used by the Marine Farmers’ Almanac as a calendrical meaning to indicate the presence of a 13th Full Moon in a tropical year which usually had 12. A tropical year is a measurement of time from one winter solstice to the next

2. When the Moon Appears Blue
There are rare occasions when the disk of the Moon appears to take on a bluish tint. These should not be confused with contrast effects in which the Moon appears blue because the viewer's eye has been `fooled' by a bright red light. Such an appearance can result from the Moon being seen next to a cloud which is strongly illuminated by the red setting Sun. By contrast, the Moon appears to be green but after the Sun's light has gone the Moon's appearance returns to normal.

A similar effect can be seen by campers sitting around the red light of a camp-fire. Their eyes become attuned to the bright red light of the fire and the Moon then appears greenish by contrast. To anyone whose eyes are not affected by the red firelight, however, the Moon appears normal.

On very rare occasions, however, the Moon does appear to have a bluish hue. This occurs after a violent volcanic eruption or, occasionally, after a big forest fire. The particles in the smoke, or in the volcanic dust, can be of just the right size to scatter the light preferentially in the red so as to leave an excess of blue light in the Moon's image. These rare events give rise to the origin of the phrase

Answer 3

When there are 2 full moons in a single month the second is called a blue moon.
Blue moon" appears to have been a colloquial expression long before it developed its calendrical senses. According to the Oxford English Dictionary, the first reference to a blue moon comes from a proverb recorded in 1528:
If they say the moon is blue,
We must believe that it is true.
Saying the moon was blue was equivalent to saying the moon was made of green (or cream) cheese; it indicated an obvious absurdity. In the 19th century, the phrase until a blue moon developed, meaning "never." The phrase, once in a blue moon today has come to mean "every now and then" or "rarely"—whether it gained that meaning through association with the lunar event remains uncertain.

Answer 4

a full moon usually occurs two times in a month and rarely , three times, this is a blue moon, the third full moon. the phrase has been around since before clocks were in use; when people used to observe time and the seasons based on the heavens.

Answer 5

look blue moon can never be seen.
so the prase is used for once in life