Blue Moon

(This 981st Buffalo Sunday News column was first published on January 10, 2010.)

Reader Jerry Lazarczyk wrote to ask, "When will we next see a blue moon on New Year's Eve?"

His query caught me off guard. I didn't even know what a blue moon is. I was also unaware that what was being called a blue moon would occur on the last day of 2009.

Clearly I had to do some homework. I did so and I share with you what I found in a variety of sources. The most informative of those sources is folklorist Philip Hiscock's article, "Once in a Blue Moon" in Sky and Telescope.

Apparently the astronomical use of blue moon derives not from a color but from an earlier word, belewe, meaning betrayer. The calculation of the date of Easter and the associated Lenten period is determined by lunar cycles. In some years a reasonable date for this religious feast did not satisfy the clergy because of an extra seasonal full moon, so that moon was rejected as a betrayer – a belewe moon.

This leads us back to Astronomy 101. The lunar months do not coincide with our calendar months. If they did, we would have full moons on the same date each month, which we certainly do not. The lunar or synodic month is about 29 1/2 days (for perfectionists: 29.53059 days or 29 days, 12 hours, 44 minutes and 3 seconds.)

Out with that calculator you so rarely use. A quick multiplication and subtraction, 365.25 - 29.53059 x 12, will show that there are about eleven extra days in our calendar year after the moon completes its twelve months. Clearly then, there will be some years when there will be two full moons in a month. In fact, this happens every two or three years (more accurately, every 2.7154 years).

Now back to history. A careful review of Farmer's Almanacs dating all the way back to 1819 by Roger Sinnott, Donald Olson, and Richard Fienberg found blue moons identified as an extra full moon occurring in a single season. Thus blue moons could only occur at the end of spring, summer, fall and winter.

It should be evident that, by this definition, the recent full moon was not a blue moon at all.

But folklore is not all ancient. We can start our own, and apparently that is exactly what happened. Hiscock's research traced the first recent occurrence of a blue moon as an extra full moon in a month to a January 1980 radio broadcast by Deborah Byrd. Ms. Byrd told him that her source was a 1946 Sky and Telescope magazine article. Thus we have the widespread use of this interpretation only over the recent thirty years.

So that is where the astronomical matter stands.

But there is more to this story. Hiscock notes a number of other uses of the phrase blue moon. The average person in the 16th century, he tells us, interpreted it as most of us do today. To them "He would argue that the moon is blue" was the equivalent of saying, "He would argue that black is white." A blue moon was as possible as the moon being made of green cheese.

That may be, but Hiscock then turns this upside down by pointing out that blue moons really have occurred. He tells us, "When the Indonesian volcano Krakatoa exploded in 1883, its dust turned sunsets green and the moon blue all around the world for the best part of two years. In 1927, the Indian monsoons were late arriving and the extra-long dry season blew up enough dust for a blue moon. And moons in northeastern North America turned blue in 1951 when huge forest fires in western Canada threw smoke particles up into the sky."

From this we derive "once in a blue moon" as an infrequent event, not quite regular enough to be determined.

In any case, if you accept the current interpretation of blue moon as the second full moon in a month, I have the answer for Lazarczyk. I understand that the next time a blue moon will occur on New Year's Eve will be in 2028. My source for that information is not an astronomer, but rather Brian Williams on the December 29 NBC Evening News.