Blue Moon

Blue Moon

A Blue Moon is the appearance of the third full moon in a season that has four full moons, instead of the usual three.Since a blue moon occurs only every two or three years, the term blue moon is used to mean a rare event, as in the phrase "once in a blue moon". (info from Wikipedia)

We went camping over the Labor Day weekend and were treated to a fairly rare occurrence. A Blue Moon. So theoretically we went camping "once in a blue moon". Actually we camp a lot and are treated to Mother Nature's beauty and bounty quite often..
I'm trying to figure out the "season" for this moon. According to the calendar, summer starts in June and ends in September.However, for this Blue Moon, the first of the four full moons is in July and the fourth comes after the first day of Fall. Since June's full moon is before the first day of Summer why is the full moon in September counted? So, I'm confused. Just like I'm confused about how they arrive at when Easter is. Not going to go into that one. If you figure it out and can relay it in terms I can understand, let me know.