Our old Plum tree became a picture for Alfred Hitchcocks 'The Birds' A wonderful Blue moon last night, not only me looking at it but this pair of Crows....The time between one full moon and the next is close to the length of a calendar month. So the only time one month can have two full moons is when the first full moon happens in the first few days of the month. The second full moon is known as a Blue moon, only in name though as it isn't actually blue, mores the pity....This happens every 2-3 years, so these sorts of Blue Moons don't come about that often.
Blue Moon, according to this definition? August 31, 2012.