Did you know we had a blue moon in December? I certainly didn’t, though I admit I haven’t been outside after dark much in the cold weather we’ve been having. Of course, if I had been out and looked at the moon, I wouldn’t have seen any blue tinge. I would have seen a full moon a few days ago, but I doubt I would have realized it was the second one since the start of December.
If I had noticed, and I’d thought about it, I’d have realized how unusual that was. When I was little, there was always a Currier & Ives calendar on the wall of the dining room across from where I sat. It showed when the new moon, first quarter moon, full moon, and last quarter moon were in each month. I didn’t understand why what looked like a half moon was called a quarter moon, and I had trouble remembering which was the full moon and which was the new moon, since they looked the same except that one was a black circle and one was a white circle. And how could anyone remember which was the first quarter and which was the last quarter, since they looked the same except that they faced opposite directions? And why wasn’t there a half moon in between the first and last quarters?
Somewhere along the way I learned enough about the moon and the calendar to know the answer to most of those questions. Though I have to admit that I still can’t tell, looking at a quarter moon, whether it is waxing or waning. And to remember the definition of “waxing” I still have to stop and remember that “waning” means to get smaller, so waxing has to be the opposite.
But apparently I missed the new definition of “blue moon” that spread in the 1980’s. It got into the Genus II version of Trivial Pursuit in 1986, which is the year I was introduced to the game and loved playing it. (I got a second-hand copy a few years ago, but it turns out I have the first Genus edition.) But with as many cards as the set has, it’s not surprising that I could play several times and never hear the question about the definition of a blue moon.
Currently it is defined as the second full moon in a calendar month. (That happens about once every two and a half years, so those old Currier and Ives calendars must have had some examples, I just didn’t happen to remember them.) But that’s a fairly new definition – after all, why would anyone call such an occurrence a “blue moon”?
Folklorist Philip Hiscock decided to do some research and find out. His answer is a fascinating example of how new meanings attach to words. The current meaning can be traced back to a March 1946 article in Sky & Telescope, which attempted to explain what a blue moon was. The magazine got it wrong, however, and introduced the now current meaning (of a second blue moon in a calendar month) in place of the previous meaning, which was the third full moon in a season (defined by the tropical year, going from one winter solstice to the next, rather than the calendar year) that had four full moons.
Hiscock’s article suggests how the phrase may have gotten started – probably connected to the also rare occasions when the moon actually does appear blue. That meaning is the one I had always assumed was the right one, though I’ve certainly never seen such a blue moon. By today’s definition, blue moons are much too predictable, even if it does require doing a bit of research to find out when the next one will occur.
There’s one other thing the phrase reminds me of – a more or less equivalent phrase that I was taught as the Spanish way to say “once in a blue moon” – cada muerte de obispo. That means “each death of a bishop” – in other words, something that happens as often as a bishop dies. I assume that means only one’s local bishop, as the phrase would have developed among people who rarely traveled, and would not be thinking of all the bishops all over Christendom. So it would be an event that was rare, but also unpredictable.