a blue moon, depending on the definition you use, is either when there are 13 full moons in one year, 4 in one quarter, or 2 in one month. There's a full moon on about December 3 some time, and again on December 31. but because full moon occurs at 19:13GMT, only places as far east as GMT+4 (Pakistan, Iran, parts of Russia, etc) will have a blue moon, since in GMT+5 (India) the blue moon is at 00:13 on January 1. Thus the late-January full moon (or the late spring full moon, or the 13th full moon in 2010) will be a blue moon east of GMT+4, while the late-December full moon will be a blue moon in GMT+4 and west of there.
A blue moon happens about once every 2.7 years, Wikipedia says. hmm...