What is a blue moon? Thats the first question I wanted to answer today. In one year, there are usually 12 full moons, but the lunar cycle allows a 13th full moon every 2 or 3 years. It happens exactly 7 times in 19 years. Blue-moon is the 13th full moon in such a year.
Last night, January 30th 2010 was a blue moon in Pakistan. First full moon of 2010 was on 1st January and then its the second full moon of the month. Hence it explains the term “once in s a blue moon”.
When does the blue moon happen? It happens in different months in different time zones. You can find the blue moon calendar here as it happens at different time of year in different time zones.