Thursday, December 31, 2009

Once in a blue moon

"Life's not all beer and skittles," so, on this last day of 2009, here is an astronomical observation.

Moon over Ashburn
In the early 20th century, the editors of the Maine Farmers' Almanac suggested that if any of the four seasons in that year contained four full Moons rather than three, the third full Moon should be called a Blue Moon. This was related to the issues of a lunar calendar (29+ days) versus a solar calendar (28, 29, 30, 31 days per month). It was also related to Christian Church methods of determining Easter Sunday, and other arcana.

Confused yet?

In the 1940s, venerable magazine Sky and Telescope was also confused. It misinterpreted the Almanac to mean a Blue Moon to be the second full moon in one calendar month. It repeated this error in 1980 on its Stardate radio broadcast.

So ... If we follow Sky and Telescope's definition, tonight is the Blue Moon —in North America. The next Blue Moon —that is, the next 2nd full moon in one calendar month— will not occur until 31 August 2012. If we follow the Farmer's Almanac, the next Blue Moon (the 3rd in one season) arrives earlier: November 21, 2010.

Tonight, here in YFGF-land, we'll have to wait for either definition of blue moon: the sky is overcast.

Happy (and safe) New Year's Eve.

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