Photosphere

Source: Wikipedia, the free encyclopedia.
This article is about the astronomical object. For the image stitching feature, see VR photography.
Not to be confused with Photon sphere.
Granules
  • Prominence
    • Not labelled: Solar wind
    A miasma of plasma
    The surface of the Sun

    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.

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

    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. 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.

    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, called metals in 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

    Solar atmosphere: temperature and density.[5] See here
    for meanings of extra lines in the graph.

    The

    kilometers thick.[9][10][11]

    Photospheric phenomena

    Further information: Solar phenomena

    In the Sun's photosphere, the most ubiquitous phenomena 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]

    References

    1. ^ Carroll, Bradley W. & Ostlie, Dale A. (1996). Modern Astrophysics. Addison-Wesley.
    2. S2CID 7297628
      .
    3. S2CID 119335130
      .
    4. S2CID 11877513
      .
    5. ^ a b 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.

    External links

    Retrieved from "https://en.wikipedia.org/w/index.php?title=Photosphere&oldid=1218212327"