Wikipedia dicit:
A corona (meaning ‘crown’ in Latin derived from Ancient Greek ‘κοÏώνη’ (korÅnè, “garland, wreath”)) is an aura of plasma that surrounds the Sun and other stars. The Sun’s corona extends millions of kilometres into outer space and is most easily seen during a total solar eclipse, but it is also observable with a coronagraph.
Spectroscopy measurements indicate strong ionization in the corona and a plasma temperature in excess of 1000000 kelvin, much hotter than the surface of the Sun.
Light from the corona comes from three primary sources, from the same volume of space. The K-corona (K for kontinuierlich, “continuous” in German) is created by sunlight scattering off free electrons; Doppler broadening of the reflected photospheric absorption lines spreads them so greatly as to completely obscure them, giving the spectral appearance of a continuum with no absorption lines. The F-corona (F for Fraunhofer) is created by sunlight bouncing off dust particles, and is observable because its light contains the Fraunhofer absorption lines that are seen in raw sunlight; the F-corona extends to very high elongation angles from the Sun, where it is called the zodiacal light. The E-corona (E for emission) is due to spectral emission lines produced by ions that are present in the coronal plasma; it may be observed in broad or forbidden or hot spectral emission lines and is the main source of information about the corona’s composition.
Video credit: Video credit: NASA’s Goddard Space Flight Center/Genna Duberstein (USRA): Producer/Mara Johnson-Groh (Wyle Information Systems): Lead Writer/Tom Bridgman (GST): Data Visualizer/Chris Smith (USRA): Narrator/Aaron E. Lepsch (ADNET): Technical Support
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