It's the celestial way of ringing in 2010.
Merrymakers looking up tonight might be treated to fireworks and confetti, but everybody will get to enjoy a New Year's Eve blue moon.
Well, as long as today's cloudy sky doesn't totally obscure it.
A blue moon refers to the second full moon in one month. The first full moon this month occurred on Dec. 2 and the second is today. The phenomenon only occurs every 2.7 years - hence the phrase "once in a blue moon." And it's rarer that the lunar event occurs on New Years Eve: around once every 20 years.
The reason we sometimes have blue moons is because of a mismatch between lunar and solar timekeeping, said David Mues, planetarium coordinator at Sacramento's Discovery Museum Science and Space Center. Our calendar is constructed so one year is one revolution of the earth around the sun, and each month is approximately one lunar cycle. But a lunar cycle is actually less than a month - 29.5 days - so once every 2.7 years, a month has more than one full moon.
The reason it's called a blue moon has nothing to do with the glowing orb's color, which will not be blue. Originally, if four full moons occurred in one season, the third was referred to as the blue moon, said Greg Laughlin, an astronomy professor at UC Santa Cruz. "Blue" moon was just one of many full moon names, such as the fall's "harvest" moon, he said.
In 1946, the magazine Sky and Telescope mistakenly referred to the blue moon by its modern definition, and it stuck.
"While most people aren't tied to the natural seasonal cycle, we do organize around the months," Laughlin said. "So it somehow has a more modern feeling."
Some locals are organizing their New Year festivities around the blue moon, such as the Sacramento Walking Sticks. They named their annual New Years Eve walk after the celestial event.
"Oh my gosh yes, I am excited," said Walking Sticks president Barbara Nuss. "I've been fascinated by the full moon for the past year and a half."
Nuss says she'll be handing out moon pies, a round pastry consisting of two graham crackers with marshmallow in the center, dipped in chocolate. She's invited an expert from the Sacramento Valley Astronomical Society to join the walk. She'll lead a few rounds of moon-themed songs, like "Moon River."
"There's just something so magical about the full moon," Nuss said. "The fact there's a blue moon on New Years is just amazing."
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