Once in a blue moon is a common English expression and it refers to a rare event. But why a blue Moon? And what is a blue Moon if it isn't blue? There is no unique answer, but here are a few things it could be.
Once in a Blue Moon The recent "blue moon" of August 20/21 2013 was the third of four full moons of the summer season. There will be a fourth one before the equinox. In England this is the Fruit Moon. What about where you live?
