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'Blue moon' is just a name in the same sense as a `hunter's moon' or a `harvest moon,"' Laughlin said in an e-mail to the Associated Press.
There's a famous song about it and a phrase that emphasizes its rarity. Now, the Bay Area will get to witness one of nature's oddest occurances.
Tonight is not only New Year's Eve, it's also the second full moon of the calendar month of December. That makes it a blue moon and the first in two years. This month's first full moon was on Dec. 2.
But this blue moon is even more special than others because it's happening on New Year's Eve -- a combination that comes only every 19 years. The last time there was a blue moon on New Year's Eve was 1990; the next one will be in 2028.
The New Year's Eve blue moon will be visible in the United States, Canada, Europe, South America and Africa. For partygoers in Australia and Asia, the full moon does not show up until New Year's Day, making January a blue moon month for them.
You'd think with it's name, the event would turn the night sky blue. But, alas, the name doesn't have anything to do with the color. 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 e-mail to the Associated Press.
So, when you howl at the moon as you're ringing in 2010, take a moment to realize that you are looking at something rare.