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.

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.

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

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.
References in periodicals archive ?
As a result, despite the realization that the spectrum of the K-corona implies that the corona is self-luminous and displays an apparent temperature no higher than that of the photosphere [2], advocates of the gaseous models of the Sun have no choice but to postulate that coronal apparent temperatures far exceed those of the solar surface.
The rigid rotation of the corona is highly suggestive that it possesses condensed matter whose associated magnetic field lines are anchored at the level of the photosphere.
Note that the apparent temperature of the photosphere (~6 000 K), does not manifest the true energy content of this region.
Having in mind this proportion, the radiation temperatures at the radii of core and photosphere (and an arbitrary radius as well) can be expressed as
In this case, to determine temperature of the photosphere, one can use the well-known formula for thermal radiation power, considering core as a radiation source:
Having in mind the evident dependence of temperature on the linear size, the temperature of the photosphere can be expressed via the temperature of the core:
Coronal material ([dagger]) contains magnetic fields lines which, in turn, are anchored at the level of the photosphere [62].
Hence, the spatial extent of the chromosphere constitutes one of the most elegant observations relative to the existence of a condensed solar photosphere.
In the same article, Herve Faye emphasized that the photospheric surface was illusionary: "This limit is in any case only apparent: the general milieu where the photosphere is incessantly forming surpasses without doubt, more or less, the highest crests or summits of the incandescent clouds, but we do not know the effective limit; the only thing that one is permitted to affirm, is that these invisible layers, to which the name atmosphere does not seem to me applicable, would not be able to attain a height of 3', the excess of the perihelion distance of the great comet of 1843 on the radius of the photosphere' [9].
James Keeler was the first to voice an objection to Schmidt's theory, responding immediately to Wilczynski's article [12]: "But however difficult it may be for present theories to account for the tenuity of the solar atmosphere immediately above the photosphere, and however readily the same fact may be accounted for by the theory of Schmidt, it is certain that the observer who has studied the structure of the Sun's surface, and particularly the aspect of the spots and other markings as they approach the limb, must feel convinced that these forms actually occur at practically the same level, that is, that the photosphere is an actual and not an optical surface.
At the same time, Langley had previously measured the solar spectrum and was setting the temperature of the photosphere at ~6,000 K.
6] K) which exceeded that of the photosphere (~6,000 K) indicated a violation of the 2nd law of thermodynamics.