Idiom meaning very rarely…

Idiom meaning very rarely, describing something that happens only occasionally. In a 1528 English pamphlet attacking the clergy, claiming that the lunar disc had an odd colour was a way of stating an obvious absurdity. Astronomers now use the term for a second full lunar phase occurring within a single calendar month, roughly every two or three years. After volcanic eruptions such as Krakatoa in 1883, it genuinely appeared tinted.

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