A full moon occured on Aug 2, 2012 and again on Aug 31, 2012

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.
The Farmers Almanac was first to call this second full moon
in one month the Blue Moon, and the name stuck.
The Christian calendar uses the blue moon for curtain dates such as Easter,
which is why Easter may vary several weeks from year to year.