Wednesday, November 9, 2011

Blue Moon

Since tonight is a Full Moon, I thought it would be fun to make a post about it.  Specifically a Blue Moon..

Tonight's Full Moon

Have you ever heard an expression "Blue Moon"? Maybe someone had said "it happens once in a blue moon"... I've heard that numerous times but never knew what that meant.  I accepted it as one of those things that just were and didn't ask any questions.

Only recently I came across an explanation of what a Blue Moon actually is and I thought I would share it with everyone.

The expression Blue Moon refers to a Full Moon of a very special kind.  As we all know Full Moon occurs once a month, precisely, every 29.53 days.  That allows for 12 full moons per year or three full moons per season.  I have to add here that by seasons I mean the seasons of the tropical year namely  winter solstice, spring equinox, summer solstice and fall equinox. Approximately every 2.75 years there will be 13 full moons in a year and therefore one season will have four full moons instead of usual three.  The third moon of that season will then be called the Blue Moon and because the event is pretty rare a phrase "once in a blue moon" was adopted as interpretation of something uncommon.

You may ask why the third moon and not the fourth is named Blue Moon.  That's because each full moon in tropical year is already assigned variety of special names such as Moon before Yule, Moon after Yule, Corn Planting Moon, Death Moon, etc..  Each and every moon has to fall in it's assigned time.  To give you an example, the first moon of summer is called the Early Summer Moon, the second is called the Midsummer Moon, and the last is called the Late Summer Moon. When a season has four moons the third is called the blue moon so that the last can continue to be called the late moon.  Similarly, when the fall has four moons, the third one will be called the Blue Moon so that the last moon of the season can still be called Moon before Yule.

During second half of the twentieth century another definition of the Blue Moon has surfaced and it states that Blue Moon is the second full moon in the month.  That is actually incorrect and results from misinterpretation of the Maine Farmers' Almanac in the March 1946 Sky & Telescope magazine. This misinterpretation was corrected in 1999.

As to where the actual name Blue Moon came from, it appears that for centuries the extra moon was called the belewe moon which translated from Old English means "betrayer" or "blue".

Isn't all that interesting?  I have to add that tonight it's not a Blue Moon.  The next Blue Moon will happen on August 21, 2013 and the last one was on November 21st, 2010. 

I hope you enjoyed the post. :)

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