The outermost layer of the Sunīs atmosphere, visible to the eye during a total solar eclipse; it can also be observed through special filters and best of all, by X-ray cameras aboard satellites. The corona is very hot, up to 1-1.5 million degrees centigrade, and is the source of the solar wind. The shape of the corona is different at solar maximum and at solar minimum.
A luminous discharge due to the ionization of the gas surrounding a conductor caused by a voltage gradient exceeding a certain critical value. It does not greatly heat the conductor, and it is limited to the region surrounding the conductor. While corona is a low energy process, over long periods of time, it can degrade insulators, causing a system to fail due to dielectric breakdown.