It’s a blue moon tonight, though it’s not really blue or green or made of cheese. It’s just that not so rare, second full moon in a month. I asked my local astronomer in residence if the moon ever appears blue. And guess what? Yes, it can be blue! And it is indeed rare and unpredictable, true to the meaning of the phrase “every once in a blue moon.”
There are several definitions of the term “Blue Moon”. Today we have an example of one of them, “the second full moon in a calendar month”. For me, this occurrence is not very interesting – a statistical artifact of our calender that has absolutely nothing to do with the Moon’s color and isn’t even particularly rare (it occurs every 3 years or so and is entirely predictable). A much rarer, far less predictable, and much more interesting situation can lead to a Blue Moon that is true to its name. (more…)
