The first full moon was on December 2
But don't expect it to be blue, for the name has nothing to do with the colour of our closest celestial neighbour.
The New Year's Eve "blue moon" will be visible over Africa, South America, the US, Canada and Europe.
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.
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.
"A very small eclipse of the full moon will be visible from all over South Africa. The eclipse starts at 8.51pm on December 31," said Dr Claire Flanagan, of the Johannesburg Planetarium at Wits University.
Partygoers will see a slight blurring of the moon.
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 be until 2028.
Blue moons had 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.
The popular definition of blue moon came about after a writer for Sky & Telescope magazine in 1946 misinterpreted the Maine Farmer's Almanac and labelled a blue moon as the second full moon in a month.
The almanac had defined a blue moon as the third full moon in a season with four full moons, not the usual three.
Although Sky & Telescope corrected the error decades later, the definition caught on.
Blue moon
Wikipedia: Blue moon
Wikipedia: Blue Moon (disambiguation)
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