As I am a big fan of all messed up creative people, let me start by quoting Lorenz Hart in one of my favorite Rogers & Hart songs:
I only bring this up because Andrea did not know what a “blue moon” was, as of this morning. At that time, she probably read something like Donna Henes’ Article on Huffington Post. It isn’t a great article, but some people are easily impressed.
Henes informs those people who don’t already know that a blue moon is the second full moon in a calendar month. This means, of course, that blue moons are meaningless because calendar months are arbitrary. But as yet another anachronistic unit of measure, the blue moon cycle is very cool: it is an odd period of time (a little less than three years) that is slightly different all of the time.
You may ask, “Why is a blue moon roughly three years in length?” But I would prefer that you not. Why? First, a blue moon is no length at all, but rather an instant. (This is not even exactly right because the moon oscillates by more than two degrees on either side and that means that even though the same part of the moon always faces us, we can see more than 50% of the surface, but I digress.) The three year number is the amount of time between blue moons.
The second reason this question is best not asked is that anyone reading this blog should really know better. But I will explain because I am kind and just. This requires some background.
You do understand that the moon does not go around the earth each night, right? I mean, pretty much the moon stays in the same place (like the sun) and it is the earth rotating at a break-neck speed that makes it look like the moon is going around the earth. In point of fact, if the earth did not rotate, the moon would move from directly overhead, all the way around the earth, and back to directly overhead in 29.5 days (roughly).
Without going into the phases of the moon, you ought to be able to conclude from this that there will be a full moon every 29.5 days (roughly). Unless you are Andrea, in which case, just take my word for it. Because of this, if you are going to squeeze a second full moon into a 30 day month, you’ve got to have your first full moon during the first 0.5 days. For a 31 day month, you have to have your first full moon during the first 1.5 days. This means you will never have a blue moon during my favorite month February when such notables are Christopher Marlowe and I were born.
On average, how often will you have a full moon on the first day of the month? About 3% of the time, right? (Andrea: just take my word.) How many months would that be? About 33, or three years, using 11 months because the sainted month of February is out.
But if all else fails, there is another song about blue moons by the great Pat Alger and Gene Levine:
15 November 2013: Added Gene Levine credit to the writing of “Once in a Very Blue Moon.”