MEANING: noun: A long time.

ETYMOLOGY From blue, from Old French bleu + moon, from Old English mona. Earliest documented use: 1702.

NOTES: The term typically appears in the phrase “once in the blue moon”, meaning rarely or not often. In reality, a blue moon occurs on average once every 2.7 years. So what is a blue moon? Well, in a year you see 12 full moons, but sometimes there’s a bonus full moon. This extra full moon is called a blue moon, though it’s not really blue.a cartoon that depicts prurient themesons. If there are four, the third full moon is called a blue moon.

Sometimes, the moon actually shows up in blue, but it has nothing to do with the above discussion -- nothing to do with a full moon. The color is due to the smoke or dust particles from forest fires, volcanic eruptions, etc.

So why is that extra moon called a blue moon? Nobody knows. Perhaps the literal blue moon got conflated with the extra full moon because both occurrences are unusual and don’t occur that often,

BLUE TOON - a cartoon that depicts prurient themes

BLÉ MOON - the full moon that occurs during the wheat harvest, usually June or July for spring wheat

BLUE MORN - the sun rose revealing a cloudless sky