Editing Stellar corona (section)

== Observable components ==

The solar corona has three recognized, and distinct, sources of light that occupy the same volume: the "F-corona" (for "Fraunhofer"), the "K-corona" (for "Kontinuierlich"), and the "E-corona" (for "emission").<ref>Golub & Pasachoff (1997). "The Solar Corona", Cambridge University Press (London), ISBN 0 521 48082 5, p. 4</ref>

The "F-corona" is named for the [[Fraunhofer lines|Fraunhofer spectrum]] of absorption lines in ordinary sunlight, which are preserved by reflection off small material objects.  The F-corona is faint near the Sun itself, but drops in brightness only gradually far from the Sun, extending far across the sky and becoming the [[zodiacal light]].  The F-corona is recognized to arise from small dust grains orbiting the Sun; these form a tenuous cloud that extends through much of the [[Solar System]].

The "K-corona" is named for the fact that its spectrum is a continuum, with no major spectral features.  It is sunlight that is [[Thomson scattering|Thomson-scattered]] by free electrons in the [[hot plasma]] of the Sun's outer atmosphere.  The continuum nature of the spectrum arises from [[Doppler broadening]] of the Sun's Fraunhofer absorption lines in the reference frame of the (hot and therefore fast-moving) electrons. Although the K-corona is a phenomenon of the electrons in the plasma, the term is frequently used to describe the plasma itself (as distinct from the dust that gives rise to the F-corona).

The "E-corona" is the component of the corona with an [[emission-line]] spectrum, either inside or outside the wavelength band of visible light.  It is a phenomenon of the ion component of the plasma, as individual ions are excited by collision with other ions or electrons, or by absorption of ultraviolet light from the Sun.