Blue moon 2009: a New Year's Eve rarity
At the end of 2009, a 鈥渂lue moon鈥� will preside over the annual New Year鈥檚 Eve countdown and accompanying ball drop in Times Square.
But what does this mean?
For most people, it will just mean a full pie in the sky Thursday night. A blue moon is simply the second full moon in month. It doesn鈥檛 actually have anything to do with color at all.
Usually, there鈥檚 only one full moon each month because the monthly calendar was built on the lunar cycle (29.5 days). But once every 2-1/2 years, those extra half days add up to two full moons in a month.
So where does the name come from?
According to , the term blue moon was "used in much the same way we use the term 'harvest moon.' There were twelve names for full moons, one for each month, and the name blue moon was used in years which had 13 full moons."
But in 1943, Sky and Telescope Magazine erroneously wrote that the second full moon in any calendar month was called a blue moon. The label stuck and is still used today.
It鈥檚 relatively rare that a blue moon would fall on New Year鈥檚 Eve. The last time that happened was 1990, according to .
Even more rare 鈥� there were two blue moons in 1999, one in January and one in March. That happens only about four times a century.
Interestingly enough, this is not where the expression 鈥渙nce in a blue moon鈥� comes from. According to NASA, that phrase is believed to have originated in 1883 after the eruption of Indonesia鈥檚 Mount Krakatoa. The volcano put so much dust in the atmosphere that the moon actually looked blue in color. The event was deemed so unusual the phrase 鈥渙nce in a blue moon鈥� was coined.
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