BEIJING, Dec. 29 (Xinhuanet) -- The last night of 2009 will boast December's second full moon, otherwise known as a blue moon, but New Year's Eve revelers won't be able to see it, according to U.S. media reports Tuesday.    

    For one thing, it won't really be blue.

    A blue moon, according to a U.S. folklore, is the appearance of a second full moon in a given month, said Bob Hayward, an astronomer and educator at Pisgah Astronomical Research Institute, the observatory in Rosman.

    Given the months with an uneven number of days in the Gregorian calendar, every couple of years will see an extra full moon in the calendar year, Hayward said.    

    That extra moon gave rise to the folklore saying “once in a blue moon,” meaning a rare occurrence. 

   “Visibly, you won't see anything different about this moon. It's just a bit of tradition,” Hayward said.

    According to Michael Paesler, head of the physics department at N.C. State University, there is such a phenomenon when the moon turns blue, but for this to happen the air must contain particles that are larger than usual; the particles scatter red light and give the moon a bluish tint. But it's an incredible rarity, Paesler said.

    The moon would not appear blue unless there is some type of optic phenomenon, said meteorologist Josh Weiss of the National Weather Service in Wilmington, N.C..

    The moon was last full at 2:30 a.m. Dec. 2. On Thursday, the moon will be exactly full at 2:13 p.m.

    The last blue moon came on May 31, 2007.   

    (Agencies)