re: #506 DEZes

Yeah, I have heard a blue moon as a 13th full moon of the year.
So that would be true as well, but 2 full moons in one month seems to be the most common among astronomers, and to take that pattern, its 3.4 blue moons per year on average.
Yes I am bored. ;)

Two per month is the common usage, regardless of the actual history.

3.4 per year sounds like an awfully high average, though. Where did you see that?