Blue Moon, the second full moon for the month of July, is seen next to the dome of the U.S. Capitol, in Washington, on Friday, July 31, 2015.

In recent years, people have used the name Blue Moon for the second of two full moons in a single calendar month. An older definition of Blue Moon is that it’s the third of four full moons in a single season.

Image Credit: NASA/Bill Ingalls

Blue Moon

source NASA