Wednesday, December 30, 2009

Blue Moon



Once in a blue moon there is one on New Year's Eve. According to popular definition, a blue moon is the second full moon in a month. But don't expect it to be blue as the name has nothing to do with the color.

The New Year's Eve blue moon will be visible in the United States, Canada, Europe, South America and Africa. The Eastern Hemisphere can celebrate with a partial lunar eclipse on New Year's Eve when part of the moon enters the Earth's shadow. The eclipse will not be visible in the Americas.

A full moon occurred on Dec. 2. It will appear again on Thursday in time for the New Year's countdown.

A full moon occurs every 29.5 days, and most years have 12. On average, an extra full moon in a month, a blue moon, occurs every 2.5 years. The last time there was a lunar double take was in May 2007. New Year's Eve blue moons are rarer, occurring every 19 years. The last time was in 1990; the next one won't come again until 2028.

Blue moons have no astronomical significance, said Greg Laughlin, an astronomer at the University of California, Santa Cruz. "'Blue moon' is just a name in the same sense as a 'hunter's moon' or a 'harvest moon,"' Laughlin said in an email.

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