A Blue Moon is the second of two full moons in one calendar month. The term originated from modern folklore. The moon doesn't actually appear to shine the color blue; rather, it looks like regular full moons.
An actual blue-tinted moon occurs most commonly following a volcanic eruption. Reports of blue-colored moons being viewed in the Western Hemisphere occurred following the eruption of Mt. St Helen's in 1980 and Mexico's El Chichon in 1983. Blue-hued moons also occur during major forest fires, such as the fire in 1953 in Alberta, Canada.
The Blue Moon also reached the entertainment world, inspiring the Elvis Presley 1956 hit of the same name.