Half Term Blue Moon

Tonight’s a Blue Moon, which happens whenever there are two full moons in a calendar month, although the phrase used to mean the third full moon of a season in which there are four in a quarter-year (or season). A Blue Moon isn’t all that rare an occurence actually. In fact there’s one every two or three years on average. But it does at least provide an excuse to post this again…

Incidentally, today marks the half-way mark in my five-year term as Head of the School of Mathematical and Physical Sciences at the University of Sussex. I started on 1st February 2013, so it’s now been exactly two years and six months. It’s all downhill from here!

9 Responses to “Half Term Blue Moon”

  1. Is that the old English spelling of average..?

  2. Bryn Jones Says:

    I had always thought the term blue moon meant those very rare occasions when the Moon appears slightly blue due to ash particles in the atmosphere after volcanic eruptions or forest fires. Then came the definition of two full moons in the same calendar month, presumably from an American folk tradition, at least to media attention.

    This changes the meaning of “once in a blue moon” from an exceptionally rare event to a rather uncommon one. That’s a significant change in meaning.

    • telescoper Says:

      The old usage of the term to denote the third moon in a sequence of four in the same quarter seems be almost completely forgotten..

      • Bryn Jones Says:

        Indeed; or never known in the first place.

        Who would use such a definition? It seems of no astronomical interest. Perhaps it is of interest to astrologers and other confused people.

      • telescoper Says:

        It appears to have been used by farmers in the 18th and 19th centuries to indicate a third moon that does not mark the end of a season.

      • Bryn Jones Says:

        I see, from the use of the lunar cycle for marking the seasons, presumably as a substitute for a calendar. I suppose it saved them forking out on a softbound almanac.

      • telescoper Says:

        How many farmers were literate in those days?

      • Bryn Jones Says:

        Literacy varied from place to place and from time to time. Probably only a minority of farmers would have had any formal education, but many could have come across basic education in Sunday schools and adult evening classes.

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