photosphere

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photosphere,

luminous, apparently opaque layer of gases that forms the visible surface of the sunsun,
intensely hot, self-luminous body of gases at the center of the solar system. Its gravitational attraction maintains the planets, comets, and other bodies of the solar system in their orbits.
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 or any other star. The photosphere lies between the dense interior gases and the more attenuated gases of the chromospherechromosphere
[Gr.,=color sphere], layer of rarefied, transparent gases in the solar atmosphere; it measures 6,000 mi (9,700 km) in thickness and lies between the photosphere (the sun's visible surface) and the corona (its outer atmosphere).
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. The incandescent gases of the photosphere, estimated to be at temperatures near 6,000°K;, are so much brighter than the other layers of the sun that they seem to form a surface. These gases are in a constant state of agitation due to convection currents that reach down to 150,000 mi (241,000 km) below the photosphere. Differences in the density of the gases result in a grainy appearance of the photosphere; the small bright patches, or granules, are several hundred miles in diameter and are constantly shifting. Another feature of the photosphere, observed only near the sun's edge, is the appearance near sunspots of bright, veinlike regions known as faculae.
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photosphere

(foh-tŏ-sfeer) The ‘visible’ surface of the Sun and source of the absorption spectrum that is characteristic of most stars. The photosphere of a star is considerably more dense than the atmospheric layers that lie above it, i.e. the chromosphere and corona.

The solar photosphere is a stratum several hundred kilometers thick, from which almost all the energy emitted by the Sun is radiated into space. Within the photosphere the temperature falls from about 6000 K just above the convective zone to about 4000 K at the temperature minimum, where the photosphere merges with the chromosphere.

The intensity of the solar photosphere, which decreases at visible wavelengths from the center to the limb of the disk (see limb darkening), is due to the radiation emitted, principally by negative hydrogen ions (H), at depths of up to a few hundred kilometers. At higher levels, where the density of H ions is too low for appreciable opacity, the lower temperature gives rise to the absorption of radiation at discrete wavelengths. The Fraunhofer lines of the resulting absorption spectrum have provided the key to determining the chemical composition of the photosphere, because a direct comparison can be made with the laboratory spectra of known elements under various conditions.

Regions of the solar photosphere (and lower chromosphere) several thousand kilometers in diameter rhythmically rise and fall with a period of about 5 minutes over a time span of less than half an hour, attaining a maximum velocity of about 0.5 km s–1. These vertical oscillations are thought to be produced by the outward propagation of low-frequency sound waves, generated by turbulence in the convective zone. The internal vibrations of the Sun, the subject area of helioseismology, can reveal information on the solar interior.

See also faculae; granulation; supergranulation; sunspots.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Photosphere

 

the deepest and densest layer of a stellar atmosphere, including the solar atmosphere, from which most of the stellar radiant energy escapes.

A large part of the continuous spectrum of stars, chiefly the visible spectrum, and most of the Fraunhofer absorption lines arise in the photosphere. The photosphere is generally in radiative equilibrium. It is easier for radiation to escape from the higher layers of a stellar atmosphere, and consequently the temperature of the star decreases as the outer layers are approached. On the average, the temperature is close to the effective temperature of the star. The size of the photosphere of the main-sequence stars (on the Hertzsprung-Russell diagram) relative to the radius of the stars is 10–4–10–3, of white dwarfs of the order of 10–6, and of giants and supergiants 10–3–10–2. The average gas densities of the photospheres of various stars vary from 10–9 g/cm3 for hot stars of the main sequence to 10–6 g/cm3 for white dwarfs.

The photosphere of the sun, which coincides with its apparent surface, has been studied in greatest detail. It is 200–300 km thick, and its temperature ranges from 4500° to 8000°K; the pressure of the gas varies from 10–5 to 10–3 dyne/cm2. The photosphere is the only region of the sun with relatively weak ionization of the sun’s predominant chemical element—hydrogen—the degree of ionization of which is about 10–4. In stars similar to the sun, the strong opacity of the photospheric gases is due to a small impurity of negative hydrogen ions.

By using a photosphere telescope it is possible to observe the fine structure of the solar photosphere—granulation—consisting of small round (about 1,000 km in diameter) bright granules that are separated by dark intergranular regions.

E. V. KONONOVICH

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

photosphere

[′fōd·ə‚sfir]
(astronomy)
The intensely bright portion of the sun visible to the unaided eye; it is a shell a few hundred miles in thickness marking the boundary between the dense interior gases of the sun and the more diffuse cooler gases in the outer portions of the sun.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
These short-lived Alfven pulses have been found to be generated by prevalent photospheric plasma swirls about the size of the British Isles, which are suggested to have a population of at least 150,000 in the solar photosphere at any moment of time.
Ono et al., "Photospheric emission from stratified jets," The Astrophysical Journal, vol.
Magnetic heating mechanisms are divided into AC and DC mechanisms, according to the ratio between the time scale [[tau].sub.c] of the convective motions which drive coronal loops at the photospheric level, and the characteristic time scale of magnetic loops, [[tau].sub.A].
We have presented here a simple technique for determining the sun's photospheric temperature, with fair accuracy, simplicity, and broad availability--ideal for the undergraduate physics classroom.
Within the context of the SSM, K-coronal polarization is thought to be produced by relativistic electrons which scatter photospheric light such that most Fraunhofer lines can no longer be observed [16, p.
We have computed the frequency [v.sub.ei] of the electron-ion collisions in the quiet photospheric conditions and reported the results in Table 1.
1989 2009 2010 Carbon 8.56 8.43 8.50 Nitrogen 8.05 7.83 7.86 Oxygen 8.93 8.69 8.76 Neon 8.09 7.93 n/a SOURCES: GEOCHIMICA ET COSMOCHIMICA ACTA 1989; ANNUAL REVIEW OF ASTRONOMY AND ASTROPHYSICS 2009; SOLAR PHYSICS 2010 Debated values Two teams have published revised estimates for photospheric metal abundances (selected ones above) that differ from 1989 values.
The density of the photospheric plasma is sufficiently high that the plasma pressure exceeds the magnetic pressure in the sunspots and so controls the motions of any magnetic fields embedded in the photosphere; the churning motions of the photosphere serve to weave and stress the magnetic fields and thus, by storing energy in the fields, create the opportunity for them to become unstable and erupt violently in the form of a flare or a CME.
[39] included the magnetic field inclination and photospheric field distribution and performed another 3D numerical MHD model for the two different types of jet events: standard and blowout jets.
In the case of magnetic bright points, it is the 'floor' which is viewed as bright, as light is said to originate from "deeper photospheric layers that are usually hotter" [138].