The Associated Press: Rare New Year’s Eve ‘blue moon’ to ring in 2010:
LOS ANGELES (AP) – Once in a blue moon there is one on New Year’s Eve.
Revelers ringing in 2010 will be treated to a so-called blue moon. According to popular definition, a blue moon is the second full moon in a month.
In fact, the “second full moon in a month” definition has become wildly popular, but as we are all well aware “popular” does not equal “correct” [ ($popular != $correct) ]. After all, the number of people who believe something has no bearing on whether that thing is correct or true.
Now, I guess it’s fitting that this is the 10 year anniversary of the Y2K brouhaha, because pointing out how wrong the “popular definition” is will tend to make me look a lot like the guy who took such pleasure a decade ago in telling us all that because there was no year zero, blah, blah, blah. So be it.
As luck would have it, just a week or so ago I followed a link on Daring Fireball to a pretty interesting article on this very subject. Turns out that the “popular definition” comes from an interpretation error made in 1946, which error was discovered in 1999 by the very magazine in which it had originally appeared!
The article, originally published in Sky & Telescope, vol. 97, no. 5 (May, 1999), is entitled What’s a Blue Moon? and the subtitle unequivocally states the fact of the matter: The trendy definition of “blue Moon” as the second full Moon in a month is a mistake. However, the article also notes that it’s unlikely that the mistake can be corrected:
With two decades of popular usage behind it, the second-full-Moon-in-a-month (mis)interpretation is like a genie that can’t be forced back into its bottle. But that’s not necessarily a bad thing. Rather than argue over whether to celebrate the dawn of the new millennium on January 1st in 2000 or 2001, those with the sunniest outlooks will celebrate twice. Why not treat Blue Moons the same way, marking both the second full Moon in a calendar month and the third full Moon in a season with four?
Which I guess is fine, but it does raise another puzzling question: just who the hell celebrates a blue Moon? 
