August 31 Blue Moon


Full moon
Full Moon (NASA Photo)


What is a Blue Moon? Several different explanations describe this infrequent occurrence.

August 31, 2012 is the second full moon of the month. This phenomenon is known as a “Blue Moon” in current discourse. This is a rather recent formulation of the term.

Sky & Telescope magazine has traced the history of the term in at least two articles and it has even been part of the change of how the term is used.

Here is a summary of what the articles describe:

  • The original usage of the term was like the modern statement “When pigs fly.”  (That will happen when the moon is blue.)
  • Another described an infrequent event related to volcanic eruptions.  The dust ejected high into the atmosphere, can give the moon and sun a bluish hue when seen through the dust.  While infrequent, blue moons do occur.
  • A usage closer to the popular modern concept can be traced to the Maine Farmers’ Almanac that related the term an extra full moon during a season.  Each season normally has three full moons.  When a season has four, the third one is called “Blue Moon.”  Historically, the full moons had season names, such as Harvest Moon, Egg Moon or Lenten Moon.  Because those full moons were related to specific events related to the seasons, there came a time when a season had an extra full moon without a name; the third month in that series was named “Blue Moon,” a sort of unnamed full moon for that infrequent occurrence.
  • Sky & Telescope also stated that it contributed to the popular notion with articles in 1946 and 1950 that cited the Maine Farmers’ Almanac, but added that a second full moon in a month was a “Blue Moon.”  This is the term that has been popularized today.

With that written, I will put here that I will not write about this topic until the next Blue Moon and let the reader determine the usage.


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Categories: Astronomy, Sky Watching

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