I ran across this piece claiming that tonight's full moon is indeed a 'blue moon'. Not the second full moon in a month as everyone *knows*, but an extra month in a season. Supposedly, the monks didn't like years with 13 full moons because it messed up their festivals... unlucky, as it were.
Sounds good to me; it even makes sense. Just goes to show that we were more than capable of viral misinformation long before the internet piped up. The caveat, of course, being that I was interested enough to read the story and post this, but not to check the article's veracity.