Corona

The outermost layer of the Sun’s outer atmosphere. This halo of ions extends millions of miles into space and consists of a gas that is much thinner than Earth’s atmosphere. The temperature is greater than one million kelvin. The corona is visible to the naked eye only during a solar eclipse.

The very hot outer layer of the Sun's atmosphere, composed of highly diffused, superheated, ionized gases, and extending into interplanetary space. Some of the hot gasses in the solar corona escape the Sun to form the solar wind.

1. The outermost layer of the solar atmosphere, characterized by low densities (< 1.0x10⁹/cc) and high temperatures (> 1.0x10⁶ K).

2. In solar-terrestrial terms, a white or colored circle or set of concentric circles of light of small radius seen around a luminous body, especially around the sun or moon. The color varies from blue inside to red outside and the phenomenon is attributed to diffraction of light by thin clouds or mist (distinguished from halo).