A very interesting phenomenon happens on the rare occasion that the rising moon is witnessed over an ocean with warm surface temperatures. The large temperature difference between the water surface and the air above it creates a mirage of a second moon in the moon's wake. At one point in the moon's rising this mirage seems to make the moon into an Omega, dubbing this phenomenon an "Omega Moon."

The full article on the latest sighting of the Omega Moon and how a photographer was lucky enough to capture it on film can be found here. Thanks Will :)