Photosphere

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The structure of the Sun, a G-type star: .mw-parser-output .div-col{margin-top:0.3em;column-width:30em}.mw-parser-output .div-col-small{font-size:90%}.mw-parser-output .div-col-rules{column-rule:1px solid #aaa}.mw-parser-output .div-col dl,.mw-parser-output .div-col ol,.mw-parser-output .div-col ul{margin-top:0}.mw-parser-output .div-col li,.mw-parser-output .div-col dd{page-break-inside:avoid;break-inside:avoid-column} Core Radiation zone Convection zone Photosphere Chromosphere Corona Sunspot Granules Prominence Not labelled: Solar wind Sun diagram.svg
The structure of the Sun, a G-type star:
  1. Core
  2. Radiation zone
  3. Convection zone
  4. Photosphere
  5. Chromosphere
  6. Corona
  7. Sunspot
  8. Granules
  9. Prominence
Not labelled: Solar wind
Sun's surface in false color Highest resolution photo of Sun (NSF) as of January 20, 2020.jpg
Sun's surface in false color

The photosphere is a star's outer shell from which light is radiated. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately 2⁄3, [1] or equivalently, a depth from which 50% of light will escape without being scattered.

Contents

A photosphere is the region of a luminous object, usually a star, that is transparent to photons of certain wavelengths.

Stars, except neutron stars, have no solid or liquid surface. [note 1] Therefore, the photosphere is typically used to describe the Sun's or another star's visual surface.

Etymology

The term photosphere is derived from Ancient Greek roots, φῶς, φωτός/phos, photos meaning "light" and σφαῖρα/sphaira meaning "sphere", in reference to it being a spherical surface that is perceived to emit light.[ citation needed ]

Temperature

The surface of a star is defined to have a temperature given by the effective temperature in the Stefan–Boltzmann law. Various stars have photospheres of various temperatures.

Composition of the Sun

The Sun is composed primarily of the chemical elements hydrogen and helium; they account for 74.9% and 23.8%, respectively, of the mass of the Sun in the photosphere. All heavier elements, colloquially called metals in stellar astronomy, account for less than 2% of the mass, with oxygen (roughly 1% of the Sun's mass), carbon (0.3%), neon (0.2%), and iron (0.2%) being the most abundant.

Sun's photosphere

Solar atmosphere: temperature and density. See here for meanings of extra lines in the graph. Sun Atmosphere Temperature and Density SkyLab.jpg
Solar atmosphere: temperature and density. See here for meanings of extra lines in the graph.

The Sun's photosphere has a temperature between 4,400 and 6,600  K (4,130 and 6,330 °C) (with an effective temperature of 5,772  K (5,499 °C)) [6] [7] meaning human eyes perceive it as an overwhelmingly bright surface, and with sufficiently strong neutral density filter, as a hueless, gray surface. It has a density of about 3×10−4 kg/m3; [8] increasing with increasing depth. [5] The Sun's photosphere is 100–400 kilometers thick. [9] [10] [11]

Photospheric phenomena

In the Sun's photosphere, the most ubiquitous phenomenon are granules—convection cells of plasma each approximately 1,000 km (620 mi) in diameter with hot rising plasma in the center and cooler plasma falling in the spaces between them, flowing at velocities of 7 km/s (4.3 mi/s). Each granule has a lifespan of only about twenty minutes, resulting in a continually shifting "boiling" pattern. Grouping the typical granules are supergranules up to 30,000 km (19,000 mi) in diameter with lifespans of up to 24 hours and flow speeds of about 500 m/s (1,600 ft/s), carrying magnetic field bundles to the edges of the cells. Other magnetically related phenomena in the Sun's photosphere include sunspots and solar faculae dispersed between granules. [12] These features are too fine to be directly observed on other stars; however, sunspots have been indirectly observed, in which case they are referred to as starspots .

Notes

  1. ↑ As of 2004, although white dwarfs are believed to crystallize from the middle out, none have fully solidified yet; [2] and only neutron stars are believed to have a solid, albeit unstable, [3] crust [4]

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<span class="mw-page-title-main">Main sequence</span> Continuous band of stars that appears on plots of stellar color versus brightness

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<span class="mw-page-title-main">Sun</span> Star at the center of the Solar System

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<span class="mw-page-title-main">Star</span> Large self-illuminated object in space

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HD 169830 is a star in the southern constellation of Sagittarius. It has a yellow-white hue and is dimly visible to the naked eye with an apparent visual magnitude of +5.90. The star is located at a distance of 120 light years from the Sun based on parallax. It is drifting closer with a radial velocity of −17.3 km/s, and is predicted to come as close as 20.7 ly (6.4 pc) in 2.08 million years. HD 169830 is known to be orbited by two large Jupiter-like exoplanets.

<span class="mw-page-title-main">Convection zone</span> Region of a star which is unstable due to convection

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<span class="mw-page-title-main">Stellar magnetic field</span> Magnetic field generated inside a star

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<span class="mw-page-title-main">Red giant</span> Type of large cool star

A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature around 5,000 K or lower. The appearance of the red giant is from yellow-white to reddish-orange, including the spectral types K and M, sometimes G, but also class S stars and most carbon stars.

HD 171238 is a star with an orbiting exoplanet in the southern constellation of Sagittarius. It is located at a distance of 145 light years from the Sun based on parallax measurements, and is drifting further away with a radial velocity of 21 km/s. The star has an absolute magnitude of 5.15, but at the distance of this system it is too faint to be viewed with the naked eye, having an apparent visual magnitude of 8.61.

<span class="mw-page-title-main">XX Trianguli</span> Star system in the constellation Taurus

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References

  1. ↑ Carroll, Bradley W. & Ostlie, Dale A. (1996). Modern Astrophysics. Addison-Wesley.
  2. ↑ Kanaan, A.; et al. (WET) (2005). "Whole Earth Telescope observations of BPM 37093: A seismological test of crystallization theory in white dwarfs". Astronomy & Astrophysics. 432 (1): 219–224. arXiv: astro-ph/0411199v1 . Bibcode:2005A&A...432..219K. doi:10.1051/0004-6361:20041125. S2CID   7297628.
  3. ↑ Jones, P. B. (2003). "Nature of Fault Planes in Solid Neutron Star Matter". The Astrophysical Journal. 595 (1): 342–345. arXiv: astro-ph/0210207 . Bibcode:2003ApJ...595..342J. doi:10.1086/377351. S2CID   119335130.
  4. ↑ Jones, P. B. (2004). "Heterogeneity of solid neutron-star matter: Transport coefficients and neutrino emissivity". Monthly Notices of the Royal Astronomical Society. 351 (3): 956–966. arXiv: astro-ph/0403400 . Bibcode:2004MNRAS.351..956J. doi: 10.1111/j.1365-2966.2004.07834.x . S2CID   11877513.
  5. 1 2 John A. Eddy (1979). "SP-402 A New Sun: The Solar Results From Skylab". NASA. Archived from the original on 2004-11-18. Retrieved 2017-07-12.
  6. ↑ "Sun Fact Sheet". nssdc.gsfc.nasa.gov. Retrieved 2023-08-27.
  7. ↑ "Resolution B3 on recommended nominal conversion constants for selected solar and planetary properties" (PDF). 2014. Archived (PDF) from the original on 2016-01-28.
  8. ↑ Stanford Solar Center (2008). "The Sun's Vital Statistics". Archived from the original on 2012-07-03. Retrieved 2018-02-20.
  9. ↑ Burnett, Don. "Search for Origins". NASA. Retrieved 5 November 2023.
  10. ↑ "The Photosphere". NASA. Retrieved 5 November 2023.
  11. ↑ "Layers of the Sun". NASA. Retrieved 5 November 2023.
  12. ↑ "NASA/Marshall Solar Physics". NASA. Archived from the original on 2016-02-05. Retrieved 2008-02-19.
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