Corona

:For other meanings, see Corona (disambiguation)

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The corona is the luminous plasma "atmosphere" of the Sun extending millions of kilometres into space, most easily seen during a total solar eclipse, but also observable in a coronagraph.

Related Topics:
Plasma - Atmosphere - Sun - Kilometre - Solar eclipse - Coronagraph

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An interesting feature of the corona is the fact that it is much hotter (by a factor of nearly 200) than the visible "surface" of the Sun: the photosphere's average temperature is 5800 kelvins compared to the corona's one to three million kelvins. The corona is 10−12 as dense as the photosphere, however, and so produces about one-millionth as much visible light. The corona is separated from the photosphere by the relatively shallow chromosphere. The exact mechanism by which the corona is heated is still the subject of some debate, but likely possibilities include induction by the Sun's magnetic field and sonic pressure waves from below (the latter being less probable now that coronae are known to be present in early-type stars). The outer edges of the Sun's corona are constantly being lost as solar wind.

Related Topics:
Photosphere - Temperature - Kelvin - Chromosphere - Magnetic field - Sonic - Star - Solar wind

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The Corona is not always evenly distributed across the surface of the sun. During periods of quiet Sun, the corona is more or less confined to the equatorial regions, with "coronal holes" covering the polar regions. However, during the Sun's active periods, the corona is evenly distributed over the equatorial and polar regions, though it is most prominent in areas with sunspot activity.

Related Topics:
Equator - Polar - Sunspot

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Generated by solar flares or large solar prominences, "coronal transients" are sometimes released. These are enormous loops of coronal material travelling outward from the Sun at over a million kilometres per hour, containing roughly 10 times the energy of the solar flare or prominence that triggered them.

Related Topics:
Solar flare - Solar prominence

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Stars other than the Sun have coronae, which can be detected using X-ray telescopes. Some stellar coronae, particularly in young stars, are much more luminous than the Sun's.

Related Topics:
X-ray - Telescope

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The high temperature of the corona gives it unusual spectral features, which led some to suggest, in the 19th century, that it contained a previously unknown element, "coronium"; however these spectral features have since been traced to known elements in high states of ionization.

Related Topics:
Spectral - 19th century - Coronium

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