Photosphere
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.
Stars, except perhaps 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
[edit | edit source]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]
Sun's photosphere
[edit | edit source]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 a 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]
Photospheric phenomena
[edit | edit source]In the Sun's photosphere, the most ubiquitous phenomenon are granules—convection cells of plasma each approximately Template:Cvt in diameter with hot rising plasma in the center and cooler plasma falling in the spaces between them, flowing at velocities of Template:Cvt. 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 Template:Cvt in diameter with lifespans of up to 24 hours and flow speeds of about Template:Cvt, 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.[11] These features are too fine to be directly observed on other stars; however, stellar spatial structures have been indirectly observed, and can behave like sunspots. We can refer to these as starspots, although clearly non-analogous features also may be present as well.
Notes
[edit | edit source]References
[edit | edit source]- ↑ Carroll, Bradley W. & Ostlie, Dale A. (1996). Modern Astrophysics. Addison-Wesley.
- ↑ 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.
- ↑ 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.
- ↑ 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.
- ↑ 5.0 5.1 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.
- ↑ "Sun Fact Sheet". nssdc.gsfc.nasa.gov. Retrieved 2023-08-27.
- ↑ "Resolution B3 on recommended nominal conversion constants for selected solar and planetary properties" (PDF). 2014. Archived (PDF) from the original on 2016-01-28.
- ↑ Stanford Solar Center (2008). "The Sun's Vital Statistics". Archived from the original on 2012-07-03. Retrieved 2018-02-20.
- ↑ "The Photosphere". NASA. Retrieved 5 November 2023.
- ↑ "Layers of the Sun". NASA. Retrieved 5 November 2023.
- ↑ "NASA/Marshall Solar Physics". NASA. Archived from the original on 2016-02-05. Retrieved 2008-02-19.
External links
[edit | edit source]
Media related to Photosphere at Wikimedia Commons- Animated explanation of the Photosphere Archived 2015-11-16 at the Wayback Machine (University of South Wales).
- Animated explanation of the temperature of the Photosphere Archived 2015-11-16 at the Wayback Machine (University of South Wales).
- Solar Lower Atmosphere and Magnetism (MPS)
_as_of_January_20,_2020.jpg){kind=link}
