Anyone hoping for something special in 2010 will get started

on the right foot: a rare blue moon will grace the skies New Year’s Eve, an event

that happens only once every 19 years.

Blue moons aren’t really blue. They’re second full moons

that fall within a single calendar month. At 29.5 days, the lunar cycle is

slightly shorter than the typical month, which puts a second full moon on a

monthly calendar every 2.5 years.

The double full moon can occur in any month, except February,

which is too short. The last time it happened on New Year’s Eve was in 1990.

The next one won’t be until 2028.

The term “blue moon” hasn’t been around for all that long. In

1937 the Almanac of Maine offered a definition of ‘blue moon’ so convoluted

that even professional astronomers struggled to understand it, according to Philip

Hiscock, folklore expert at Memorial University of Newfoundland.

“It involved factors such as the ecclesiastical dates of

Easter and Lent, and the timing of seasons according to the dynamical mean sun.

Aiming to explain blue moons to the layman, Sky & Telescope published an article in 1946 titled ‘Once in a Blue

Moon.’ The author, James Hugh Pruett , cited the 1937 Maine almanac and opined

that the ‘second [full moon] in a month, so I interpret it, is called Blue

Moon,’ ” Hiscock said in a NASA press release.

The assessment wasn’t right, but the term stuck nonetheless. 

Enjoy the sight and Happy New Year.