Tonight is the real 'Once in a Blue Moon'

There are two definitions of a blue moon. 

One is when there are two full moons in a month, but that definition was a mistake, according to Mother Nature Network.  The common definition is the third full moon in a season with four full moons. Most have three.

It's also called the Full Sturgeon Moon, the Full Red Moon, the Green Corn Moon and the Grain Moon. Check this article to find out why.