Once in a blue moon
Once in a blue moon
Rarely, once in a very long time, as in We only see our daughter once in a blue moon. This term is something of amisnomer, because an actual blue moon-that is, the appearance of a second full moon in the same calendar month-occurs every 32 months or so. Further, the moon can appear blue in color at any time, depending on weatherconditions. [Early 1800s
Etymology: based on the informal phrase blue moon (the second time in one
month that you can see the full disk of themoon )
ALSO: A great tune by Van Morrison!
