28 Dec 2007
Where does the saying "Once in a blue moon" come from and what does it mean?

I was reading Reader's Digest (November 07 copy) and somehow came across the meaning of "Once in a blue moon" (My favourite phrase, haha):

It is believed that at some point in the 19th century, "blue moon" took on a literal meaning: When dust from volcanic eruptions and/or smoke from forest fires in the air made the moon appear somewhat blue. These were fairly occurrences, hence the term "Once in a blue moon" - the meaning of which has not changed (Reader's Digest, 2007)