Even though today, the phrase Once in a Blue Moon implies an event that happens rarely, the event itself isn’t the origin of the phrase. (Phew!)
And even though the appearance of a Moon that actually looks blue can happen given the right atmospheric circumstances (see, Can the Moon Appear Blue) a ‘Blue Moon’ was originally considered something that was impossible – not rare.
Thanks to Phrase Finder, I now know the relationship of the expression with an impossibility dates back to England during the Age of Discovery, and can be found mentioned in the Treatyse of the Buryall of the Masse (1528), a work by William Barlow, who, at the time, was the Bishop of Chichester:
Yf they saye the mone is belewe,
We must beleve that it is true.
And then, in 1529, A pistle to the christen reader, an essay by John Frith included the following:
“They wold make men beleue… that ye mone is made of grene chese.”
These two similar abstract ideas – ‘the moon is blue’ and ‘the moon is made of green cheese’ – were synonyms used to express an obvious absurdity, something of which there could be no doubt whatsoever – an impossibility.
These days we simply say ‘pigs might fly’, or ‘when hell freezes over’. At least that’s what we said 20 or 30 years ago. Perhaps today it’s another new saying that means something impossible.
It took several hundred years for the expression Once in a Blue Moon come to mean something that happens rarely, and I’m very pleased it’s no longer an impossibility.
– ⋅ o ♥ o ⋅ –
Here’s something else that’s not quite an impossibility – Me getting out of bed to photograph the Moon, although this morning, I missed it 😦
With only one more day until it reaches full, it was illuminating our bedroom like a lighthouse beacon and I thought: “I’ll just go grab my camera!” It was 4:18 am, but by the time I got dressed and got outside, the Moon had slipped below the tree line.

I’m aiming for better luck tomorrow night when a big, beautiful Moon rises around 4:30 pm.
This is my next entry in my Blue Moon Squares as part of Becky’s ‘Blue’ Square in July photo challenge.
In case you’re wondering if all that moonlight woke me . . .
. . . it didn’t.
But the temperature did.
See the ‘Feels like’ – it has a minus sign in front of it.
Brrr, no wonder I was cold.
And for those who prefer Fahrenheit, that’s 31.1 – just below freezing.
I should have had another blanket on the bed, and I will tonight.
Makes an impressive photo behind the tree, so can’t wait to see it above!
And how fascinating about the phrase . . .learning so much about moons 🙂
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😊😊😊
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Thanks for the information. I hope you get your picture of the moon but I loved the picture in the trees.
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Thank you, Busy Lady 🙂 I do like the photo too.
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You are welcome.
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