About once every 19 years, February has no full moon at all. Moreover, in 7 out of every 19 years, two full moons will fall in the same calendar month. The second of the month’s two full moons is popularly referred to as a Blue Moon. The name Blue Moon accounts for times when there are more full moons than is ordinary, and for this round, the 'blue moon' is actually referring to the second full moon in the month of August 2012. We already had a full moon om 1st August 2012 and tonite, there is another round of full moon!! :)
http://earthsky.org/astronomy-essentials/when-is-the-next-blue-moon
