Thursday, 29 July 2010

What is a Blue Moon?

You've probably heard the phrase "once in a blue moon", meaning rather infrequently. But what is a Blue Moon?

According to the popular definition, it is the second full moon to occur in a single calendar month. On average, there will be 41 months that have two full moons in every century, so you could say that once in a Blue Moon actually means once every two-and-a-half years.

But that's not the only definition!

In Sky and Telescope, 1946, the author of an article on full moons, gave the current definition. He was working from the 1937 Maine Farmers' Almanac which listed full moons, but it seems that he made a mistake!

In fact, checking back entries to 1819, it seems clear the Almanac used the term Blue Moon to mean the third full moon in a season which has four. Not the same as our popular definition!

The folklore historian Philip Hiscock has traced six different meanings of the term blue moon over the centuries. He find the earliest use of the term to mean something absurd, that cannot be, like "The Moon is made of Green Cheese". The earliest citation is a 1528 poem "Rede Me and Be Not Wroth":
"Yf they say the mone is blewe
We must believe that it is true."

This lead to the second meaning of "never" - a blue moon was an impossible event, which never happened.

The third meaning was a literal blue moon, which happened, for instance, after Krakatoa exploded. Because this visual event was rare, it lead to the fourth meaning of "not very often at all".

Meaning five uses it as a symbol of loneliness and sadness, as with singing the blues. Moon river....

Meaning six was that given in the Almanac, or its misinterpretation, of two full moons in a calendar month; this does not appear in any records before 1937!!!

So what is a blue moon?

Most of these definitions sum up how we perceive the moon, and its effect on us, and our lives. In this respect, the current definition is marking time as special by the phases of the moon, and marking the moons attraction on us. The pattern of our lives as with all life on earth, follows solar cycles and lunar cycles.

But there is also a cultural cycle imposed upon this, a pattern of reason, which has fashioned the calendar months away from the lunar cycle. These are a human creation, and we live our lives according to those patterns which we have created as well. So the blue moon, as the current definition has it, marks a special overlap between the lunar cycle and the social/cultural pattern, and this gives it a distinctive merit.

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