chromosphere

Astronomy a gaseous layer of the sun's atmosphere extending from the photosphere to the corona and visible during a total eclipse of the sun

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

chromosphere

(kroh -mŏ-sfeer) The stratum of a star's atmosphere immediately above the photosphere and below the corona. The chromosphere is considerably less dense than the photosphere, and its gases are characterized by an emission rather than an absorption spectrum. The best-studied chromosphere is that of the Sun.

In the solar chromosphere the temperature rises over a few thousand kilometers from about 4000 K at the temperature minimum to around 50 000 K at the transition region (see Sun). The rise in temperature (which continues in the transition region and inner corona) was once thought to be the result of ascending shock waves, but this mechanism does not tally with detailed observations of the coronae of the Sun and other stars. It is now believed that magnetic heating is responsible (see corona).

The solar chromosphere is visible under natural circumstances only when the photosphere is totally eclipsed by the Moon (see eclipse). It is then seen in profile at the Sun's limb. It may, however, be observed at times other than totality with the aid of a spectroheliograph/spectrohelioscope or a telescope equipped with a suitable narrow-band interference filter. See also chromospheric network; flash spectrum; spicules.

Chromospheres of other stars are studied by observing their strong ultraviolet emission lines or the narrow optical emission lines seen in the center of their photospheric broad absorption lines. In many stars of similar spectral type to the Sun, the chromospheric emission changes with a period of several years, indicating the presence of a cycle of activity akin to the solar cycle (see sunspot cycle). Chromospheric brightness is related to speed of rotation, being greater for stars that rotate rapidly (either because they are young or because of the effect of a companion – see RS Canum Venaticorum star).

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

chromosphere

[′krȯ·mə‚sfir]

(astronomy)

A transparent, tenuous layer of gas that rests on the photosphere in the atmosphere of the sun.

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References in periodicals archive

During a solar eclipse, the flash spectrum associated with the chromosphere of the Sun becomes readily visible [2-5].

The liquid metallic hydrogen model of the sun and the solar atmosphere VIII. 'Futile' processes in the chromosphere

While hydrogen-[alpha] emissions are responsible for the red glow of the chromosphere visible during an eclipse, this region of the Sun also emits a weak continuous spectrum [56] which has drawn the attention of solar observers for more than 100 years [140-147].

Forty lines of evidence for condensed matter--the sun on trial: liquid metallic hydrogen as a solar building block

In order to further increase this scale height to the levels observed, it was hypothesized that the chromosphere had to be heated, either through turbulent motion, wave motion, magnetic fields, or 5-minute oscillations [277, p.

Forty lines of evidence for condensed matter--the sun on trial: liquid metallic hydrogen as a solar building block

I watched it thus, for over a minute,' he later wrote, 'but it gradually merged into the background darkness as it moved farther away, and was irretrievably lost just before 13h.19m.' The explanation, he proposed, 'would seem to be that the planet was being projected against a low intensity suffusion of light (not visually apparent) from the lower chromosphere.' (12)

Mercury projected on the solar corona

Models based on this picture successfully predict the intensity and color of light emitted by a variety of atoms in the sun's chromosphere. But they cannot readily match measurements of the intensity of certain wavelengths of infrared light emitted by carbon monoxide molecules.

Big chill in the solar atmosphere

It's unclear whether they are a new type of blast or a hotter analog to "Ellerman bombs," which are created when a small, U-shaped magnetic loop in the chromosphere dips down into the photosphere, pinches off, and dumps its energy.

Sun: IRIS finds solar tornadoes, bombs

Since then, great attention has been given to identifying the lines which are contained within the flash spectrum of the chromosphere, particularly through the efforts of astronomers like John Evershed [9,10] and Donald Menzel [11,12].

Commentary relative to the emission spectrum of the solar atmosphere: further evidence for a distinct solar surface

Usually comets do not survive because of the Sun's over powering heat but this one apparently did, and disappeared in the chromosphere, evaporating in the 100,000-degree (Kelvin) heat.

Scientists capture collision of a comet and Sun

it may also lift charged particles from the sun's dense lower atmosphere, or chromosphere. These particles fill the series of closely spaced magnetic loops that form an arcade high in the corona.

Solar outbursts