A corona describes one or more luminous disks of light that sometimes appear around the sun or moon. Corona means crown. These optical phenomena are created by light diffraction, which is the slight bending of light as it passes by the edge of an object. When sunlight passes through a cloud, the light is diffracted by water droplets in the cloud and white light is separated into the many different colors that make up the corona. Coronas are widespread, but rare and usually occur in the winter over mountaintops. Here is an image of a lunar corona.
