Full thunder moon

This month will see two full moons...

What is a Blue Moon?

The modern day definition of a Blue Moon is when there are 2 full moons in one Month. A full moon occurs roughly every 29.5 days and on the rare occasions when the full moon falls at the very beginning of a month there is a good chance a Blue Moon will occur at the end of the month. According to this definition the next blue moon will occur on July 31, 2015.
The last blue moon occured in August 2012 and the next one will be in January 2018...
Source :  www.moongiant.com