Have you even heard the American English idioms...Once in a blue moon.
It doesn't mean that the moon is blue. So let's listen to this American English conversation to find out how
it is used:
A: Where did you say your brother lives?
B: He lives all the way in Minnesota, so I never get to see him. I only get to see him once in a blue moon.
Once in a blue moon is a common way of saying that something does not happen often. But what is a blue moon?
We typically see a full moon once a month. And seeing two full moons in the same month is rare. The second full moon in a particular month is called the blue moon.
Once in a blue moon is an informal phrase.
And that's English in a Minute.