corona (solar and lunar)

An atmospheric optical phenomenon due to the diffraction of light, consisting of a set of colored rings - rarely more than three - surrounding the solar or lunar disk, arranged concentrically around it. The intensity of the colors is directly proportional to the uniformity of the size of the small water drops in which the light is diffracted, while the radius of the corona is inversely proportional to that size. The inner part of this photometeor is known as the aureole. The outermost layer of the sun, composed of plasma, at a temperature on the order of a million degrees Celsius, is also called the solar corona. See also solar storm.