chromosphere

—chromospheric /kroh'meuh sfer"ik, -sfear"-/, adj.

/kroh"meuh sfear'/, n. Astron.

1. a scarlet, gaseous envelope surrounding the sun outside the photosphere, from which enormous quantities of hydrogen and other gases are erupted.

2. a gaseous envelope surrounding a star.

[1865-70; CHROMO- + -SPHERE]

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Layer of the Sun's atmosphere, several thousand miles thick, above the photosphere and below the corona.

The chromosphere (literally "colour sphere") is briefly visible as a thin ring, red from hydrogen's emission spectrum, during solar eclipses when the photosphere is obscured by the Moon. At other times it can be observed only with special instruments. Its temperatures range from about 7,000 °F (4,000 °C) about 700 mi (1,100 km) above the photosphere, increasing with altitude to several hundred thousand degrees. Solar flares and solar prominences are mainly chromospheric phenomena.

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▪ solar

      lowest layer of the Sun's atmosphere, several thousand kilometres thick, above the bright photosphere and below the extremely tenuous corona. Named by the English astronomer Joseph Norman Lockyer in 1868, the chromosphere (colour sphere) appears briefly as a bright crescent, red with hydrogen light, during solar eclipses when the body of the Sun is almost obscured by the Moon. Except during eclipses, it can be observed only with special instruments—i.e., the spectroheliograph or coronagraph. The lower chromosphere was formerly called the reversing layer because it was thought to be responsible for producing the dark lines of the solar spectrum that appear reversed against the bright continuous spectrum; actually the weak dark lines and bright continuum can be produced in essentially the same regions, stronger lines being produced at higher levels. The term reversing layer is now seldom used. The lower chromosphere is more or less homogeneous; the upper contains comparatively cool columns of ascending gas known as spicules, having between them hotter gas much like that of the corona, into which the upper chromosphere merges gradually. Temperatures in the chromosphere range from about 4,500 to 100,000 K, increasing with altitude. Solar flares and prominences are primarily chromospheric phenomena.

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