Editing Photosphere

{{short description|Star's outer shell from which light is radiated}}
{{about|the astronomical concept|the image stitching feature|VR photography}}
{{distinguish|Photon sphere}}
[[File:Highest resolution photo of Sun (NSF) as of January 20, 2020.jpg|thumb|alt=A miasma of plasma|Sun's surface in false color|228x228px]]
The '''photosphere''' is a star's outer shell from which [[light]] is radiated. It extends into a star's surface until the [[plasma (physics)|plasma]] becomes opaque, equivalent to an [[optical depth]] of approximately {{frac|2|3}},<ref>{{cite book
|last1=Carroll |first1=Bradley W.
|last2=Ostlie |first2=Dale A.
| name-list-style=amp
| date=1996
| title=Modern Astrophysics
| publisher=[[Addison-Wesley]]
}}</ref> 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 [[wavelength]]s.

Stars, except [[neutron star]]s, have no solid or liquid surface.{{NoteTag|As of 2004, although white dwarfs are believed to crystallize from the middle out, none have fully solidified yet;<ref>{{cite journal |arxiv=astro-ph/0411199v1 |collaboration=WET|doi=10.1051/0004-6361:20041125|title=Whole Earth Telescope observations of BPM 37093: A seismological test of crystallization theory in white dwarfs|year=2005|last1=Kanaan|first1=A.|last2=Nitta|first2=A.|last3=Winget|first3=D. E.|last4=Kepler|first4=S. O.|last5=Montgomery|first5=M. H.|last6=Metcalfe|first6=T. S.|last7=Oliveira|first7=H.|last8=Fraga|first8=L.|last9=Da Costa|first9=A. F. M.|last10=Costa|first10=J. E. S.|last11=Castanheira|first11=B. G.|last12=Giovannini|first12=O.|last13=Nather|first13=R. E.|last14=Mukadam|first14=A.|last15=Kawaler|first15=S. D.|last16=O'Brien|first16=M. S.|last17=Reed|first17=M. D.|last18=Kleinman|first18=S. J.|last19=Provencal|first19=J. L.|last20=Watson|first20=T. K.|last21=Kilkenny|first21=D.|last22=Sullivan|first22=D. J.|last23=Sullivan|first23=T.|last24=Shobbrook|first24=B.|last25=Jiang|first25=X. J.|last26=Ashoka|first26=B. N.|last27=Seetha|first27=S.|last28=Leibowitz|first28=E.|last29=Ibbetson|first29=P.|last30=Mendelson|first30=H.|journal=Astronomy & Astrophysics|volume=432|issue=1|pages=219–224|bibcode=2005A&A...432..219K|s2cid=7297628|display-authors=1}}</ref> and only neutron stars are believed to have a solid, albeit unstable,<ref>{{cite journal |arxiv=astro-ph/0210207|doi=10.1086/377351|title=Nature of Fault Planes in Solid Neutron Star Matter|year=2003|last1=Jones|first1=P. B.|journal=The Astrophysical Journal|volume=595|issue=1|pages=342–345|bibcode=2003ApJ...595..342J|s2cid=119335130}}</ref> crust <ref>{{cite journal |doi=10.1111/j.1365-2966.2004.07834.x|title=Heterogeneity of solid neutron-star matter: Transport coefficients and neutrino emissivity|year=2004|last1=Jones|first1=P. B.|journal=Monthly Notices of the Royal Astronomical Society|volume=351|issue=3|pages=956–966|doi-access=free |arxiv=astro-ph/0403400|bibcode=2004MNRAS.351..956J|s2cid=11877513}}</ref>}} 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|date=March 2021}}

== 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 [[Metallicity|''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 ==
[[Image:Sun Atmosphere Temperature and Density SkyLab.jpg|thumb|upright|[[Solar atmosphere]]: temperature and density.<ref name=Eddy /> See [[File talk:Sun Atmosphere Temperature and Density SkyLab.jpg|here]] for meanings of extra lines in the graph.]]

The [[Sun]]'s photosphere has a temperature between {{convert|4400|and|6600|K|°C|lk=in}} (with an effective temperature of {{convert|5772|K|°C|lk=in}})<ref>{{Cite web |title=Sun Fact Sheet |url=https://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html |access-date=2023-08-27 |website=nssdc.gsfc.nasa.gov}}</ref><ref>{{Cite web |date=2014 |title=Resolution B3 on recommended nominal conversion constants for selected solar and planetary properties |url=https://iau.org/static/resolutions/IAU2015_English.pdf |url-status=live |archive-url=https://web.archive.org/web/20160128180606/https://iau.org/static/resolutions/IAU2015_English.pdf |archive-date=2016-01-28}}</ref> 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{{e|-4}} [[kilogram|kg]]/[[cubic meter|m<sup>3</sup>]];<ref name="Stanford University">{{cite web| url=http://solar-center.stanford.edu/vitalstats.html| title=The Sun's Vital Statistics| author=Stanford Solar Center| year=2008| access-date=2018-02-20| archive-date=2012-07-03| archive-url=https://web.archive.org/web/20120703061116/http://solar-center.stanford.edu/vitalstats.html| url-status=live}}</ref> increasing with increasing depth.<ref name=Eddy>{{cite web | url = https://history.nasa.gov/SP-402/p2.htm | title = SP-402 A New Sun: The Solar Results From Skylab | author = John A. Eddy | year = 1979 | publisher = NASA | access-date = 2017-07-12 | archive-date = 2004-11-18 | archive-url = https://web.archive.org/web/20041118125616/https://history.nasa.gov/SP-402/p2.htm | url-status = live }}</ref> The Sun's photosphere is 100–400 kilometers thick.<ref>{{cite web |last1=Burnett |first1=Don |title=Search for Origins |url=https://solarsystem.nasa.gov/genesismission/ |website=NASA |access-date=5 November 2023}}</ref><ref>{{cite web |title=The Photosphere |url=https://solarscience.msfc.nasa.gov/surface.shtml |website=NASA |access-date=5 November 2023}}</ref><ref>{{cite web |title=Layers of the Sun |url=https://www.nasa.gov/image-article/layers-of-sun/ |website=NASA |access-date=5 November 2023}}</ref>

== Photospheric phenomena ==
{{Further|Solar phenomena}}

In the Sun's photosphere, the most ubiquitous phenomenon are [[Granule (solar physics)|granules]]—[[convection cell]]s of [[Plasma (physics)|plasma]] each approximately {{cvt|1000|km|mi|sp=us}} in diameter with hot rising plasma in the center and cooler plasma falling in the spaces between them, flowing at velocities of {{cvt|7|km/s|mi/s|sp=us}}. Each granule has a lifespan of only about twenty minutes, resulting in a continually shifting "boiling" pattern. Grouping the typical granules are [[Supergranulation|supergranule]]s up to {{cvt|30,000|km|mi|sp=us}} in diameter with lifespans of up to 24 hours and flow speeds of about {{cvt|500|m/s|ft/s|sp=us}}, carrying [[magnetic field]] bundles to the edges of the cells. Other magnetically related phenomena in the Sun's photosphere include [[sunspot]]s and solar [[Solar facula|facula]]e dispersed between granules.<ref>{{cite web| url=http://solarscience.msfc.nasa.gov/feature1.shtml| title=NASA/Marshall Solar Physics| publisher=[[NASA]]| access-date=2008-02-19| archive-date=2016-02-05| archive-url=https://web.archive.org/web/20160205053236/http://solarscience.msfc.nasa.gov/feature1.shtml| url-status=live}}</ref> 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 ''[[starspot]]s''.

== Notes ==
{{NoteFoot}}

== References ==
{{Reflist}}

== External links ==
*{{Commons category-inline}}
* [http://alienworlds.southwales.ac.uk/sunStructure.html#/photosphere Animated explanation of the Photosphere ] (University of South Wales).
* [http://alienworlds.southwales.ac.uk/sunStructure.html#/photospheretemp Animated explanation of the temperature of the Photosphere] (University of South Wales).
* [http://www.mps.mpg.de/solar-physics/slam Solar Lower Atmosphere and Magnetism] ([[Max Planck Institute for Solar System Research|MPS]])

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