where did the phrase out of the blue come from
Out of the blue (idiom) "Out of the blue" is an informal English language idiom that describes an event that occurs unexpectedly, without any warning or preparation.[1] It is used as an adverb. The "blue" in the phrase refers to the sky, one from which a sudden thunderstorm is unexpected.[2]
Blue moon Owing to the rarity of a blue moon, the term "blue moon" is used colloquially to mean a rare event, as in the phrase "once in a blue moon".[4][5]