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Stellar atmosphere
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<h2 id="overview">Overview</h2> <p>The stellar atmosphere is divided into several regions of distinct character: </p> <ul><li>The <a href="/facts/Photosphere/32a139LB">photosphere</a>, which is the atmosphere's lowest and coolest layer, is normally its only visible part.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> <a href="/facts/Light/jeofpMn4">Light</a> escaping from the surface of the star stems from this region and passes through the higher layers. The <a href="/facts/Sun/CadPCVHh">Sun</a>'s photosphere has a <a href="/facts/Effective_temperature/RY30DaSY">temperature</a> in the 5,770–5,780 <a href="/facts/Kelvin/E3trzC4C">K</a> (5,500–5,510 <a href="/facts/Celsius/okAEu1CA">°C</a>; 9,930–9,940 <a href="/facts/Fahrenheit/2TVmyJod">°F</a>) range.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a><a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> <a href="/facts/Starspot/Hc16g7mJ">Starspots</a>, cool regions of disrupted <a href="/facts/Magnetic_field/Ta8Ev588">magnetic field</a>, lie in the photosphere.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a></li> <li>Above the photosphere lies the <a href="/facts/Chromosphere/TurLRnLk">chromosphere</a>. This part of the atmosphere first cools down and then starts to heat up to about 10 times the temperature of the photosphere.</li> <li>Above the chromosphere lies the <a href="/facts/Solar_transition_region/fwsuHRhk">transition region</a>, where the temperature increases rapidly on a distance of only around 100 km (62 mi).<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a></li> <li>Additionally, many stars have a molecular layer (MOLsphere) above the photosphere and just beyond or even within the chromosphere.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> The molecular layer is cool enough to contain molecules rather than plasma, and may consist of such components as carbon monoxide, water vapor, silicon monoxide, and titanium oxide.</li> <li>The outermost part of the stellar atmosphere, or upper stellar atmosphere, is the <a href="/facts/Stellar_corona/W4WNqV9u">corona</a>, a tenuous <a href="/facts/Plasma_(physics)/1d3btMVU">plasma</a> which has a temperature above one million Kelvin.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> While all stars on the <a href="/facts/Main_sequence/DJ3Wq8kd">main sequence</a> feature transition regions and coronae, not all <a href="/facts/Stellar_evolution/Qa4vAGmn">evolved stars</a> do so. It seems that only some <a href="/facts/Giant_star/kMseY7qf">giants</a>, and very few <a href="/facts/Supergiant/y7w8WEcm">supergiants</a>, possess coronae. <a href="/facts/Stellar_corona/W4WNqV9u">An unresolved problem</a> in stellar <a href="/facts/Astrophysics/krFPRWLA">astrophysics</a> is how the corona can be heated to such high temperatures. The answer is believed to lie in <a href="/facts/Magnetic_field/Ta8Ev588">magnetic fields</a>, but the exact mechanism remains unclear.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a></li> <li>The <a href="/facts/Astrosphere/hjIcT4u0">astrosphere</a>, which is in the case of the Sun the <a href="/facts/Heliosphere/Yc9ToWbA">heliosphere</a>,<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> can be in a broader understanding considered the furthest part of a stellar atmosphere,<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a><a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> before <a href="/facts/Interstellar_space/R3LRKyFs">interstellar space</a> begins at the <a href="/facts/Heliopause_(astronomy)/Yc9ToWbA">heliopause</a>. The astrosphere is not to be confused with the <a href="/facts/Solar_System/QIcLSazQ">Solar System</a> and its outermost region the <a href="/facts/Oort_cloud/wdP3VNxd">Oort cloud</a>, which extends much further than the astrosphere, therefore far into interstellar space.</li></ul> <p>During a total <a href="/facts/Solar_eclipse/2XsCFG1a">solar eclipse</a>, the photosphere of the Sun is <a href="/facts/Occultation/a9Q1KTPe">obscured</a>, revealing its atmosphere's other layers.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> Observed during eclipse, the Sun's chromosphere appears (briefly) as a thin pinkish <a href="/facts/Arc_(geometry)/xBQ0pTBW">arc</a>,<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> and its corona is seen as a tufted <a href="/facts/Halo_(optical_phenomenon)/QgmnIgWQ">halo</a>. The same phenomenon in <a href="/facts/Binary_star/TYlDe1bD">eclipsing binaries</a> can make the chromosphere of giant stars visible.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Cecilia_Payne-Gaposchkin/omItk5SS">Cecilia Payne-Gaposchkin</a>, who first proposed the presently-accepted composition of stellar atmospheres</li> <li><a href="/facts/Circumstellar_envelope/8YvSMX5l">Circumstellar envelope</a></li> <li><a href="/facts/Heliosphere/Yc9ToWbA">Heliosphere</a></li></ul> <h2 id="notes">Notes</h2> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>""Beyond the Blue Horizon" – A Total Solar Eclipse Chase". 1999-08-05. Retrieved 2010-05-21. On ordinary days, the corona is hidden by the blue sky, since it is about a million times fainter than the layer of the sun we see shining every day, the photosphere. <a href="https://www.sciencedaily.com/releases/1999/08/990805111308.htm" target="_blank">https://www.sciencedaily.com/releases/1999/08/990805111308.htm</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Mariska, J. T. (1992). The solar transition region. Cambridge Astrophysics Series. Cambridge University Press. ISBN 978-0-521-38261-8. <a href="978-0-521-38261-8" target="_blank">978-0-521-38261-8</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Lang, K. R. (September 2006). "5.1 MAGNETIC FIELDS IN THE VISIBLE PHOTOSPHERE". Sun, earth, and sky (2nd ed.). Springer. p. 81. ISBN 978-0-387-30456-4. this opaque layer is the photosphere, the level of the Sun from which we get our light and heat <a href="978-0-387-30456-4" target="_blank">978-0-387-30456-4</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Lang, K. R. (September 2006). "5.1 MAGNETIC FIELDS IN THE VISIBLE PHOTOSPHERE". Sun, earth, and sky (2nd ed.). Springer. p. 81. ISBN 978-0-387-30456-4. this opaque layer is the photosphere, the level of the Sun from which we get our light and heat <a href="978-0-387-30456-4" target="_blank">978-0-387-30456-4</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Mariska, J. T. (1992). The solar transition region. Cambridge University Press. p. 60. ISBN 978-0-521-38261-8. 100 km suggested by average models <a href="978-0-521-38261-8" target="_blank">978-0-521-38261-8</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Tsuji, Takashi (2006). "Infrared Spectra and Visibilities as Probes of the Outer Atmospheres of Red Supergiant Stars". The Astrophysical Journal. 645 (2): 1448–1463. doi:10.1086/504585. S2CID 119426022. <a href="https://doi.org/10.1086%2F504585" target="_blank">https://doi.org/10.1086%2F504585</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>R.C. Altrock (2004). "The Temperature of the Low Corona During Solar Cycles 21–23". Solar Physics. 224 (1–2): 255. Bibcode:2004SoPh..224..255A. doi:10.1007/s11207-005-6502-4. S2CID 121468084. <a href="https://zenodo.org/record/1232838" target="_blank">https://zenodo.org/record/1232838</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>"The Sun's Corona – Introduction". NASA. Retrieved 2010-05-21. Now most scientists believe that the heating of the corona is linked to the interaction of the magnetic field lines. <a href="https://imagine.gsfc.nasa.gov/docs/science/mysteries_l1/corona.html" target="_blank">https://imagine.gsfc.nasa.gov/docs/science/mysteries_l1/corona.html</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Sterken, Veerle J.; Baalmann, Lennart R.; Draine, Bruce T.; Godenko, Egor; Herbst, Konstantin; Hsu, Hsiang-Wen; Hunziker, Silvan; Izmodenov, Vladislav; Lallement, Rosine; Slavin, Jonathan D. (2022). "Dust in and Around the Heliosphere and Astrospheres". Space Science Reviews. 218 (8). Springer Science and Business Media LLC. doi:10.1007/s11214-022-00939-7. hdl:20.500.11850/585419. ISSN 0038-6308. <a href="https://doi.org/10.1007%2Fs11214-022-00939-7" target="_blank">https://doi.org/10.1007%2Fs11214-022-00939-7</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>"Sun: Facts". NASA Science. 2017-11-14. Retrieved 2023-10-11. <a href="https://science.nasa.gov/sun/facts/" target="_blank">https://science.nasa.gov/sun/facts/</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>"Components of the Heliosphere". NASA. 2013-01-25. Retrieved 2023-10-11. <a href="https://www.nasa.gov/image-article/components-of-heliosphere/#:~:text=influence%20in%20space.-,The%20Heliosphere%20is%20the%20outer%20atmosphere%20of%20the%20Sun%20and,planets%20in%20our%20solar%20system." target="_blank">https://www.nasa.gov/image-article/components-of-heliosphere/#:~:text=influence%20in%20space.-,The%20Heliosphere%20is%20the%20outer%20atmosphere%20of%20the%20Sun%20and,planets%20in%20our%20solar%20system.</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>""Beyond the Blue Horizon" – A Total Solar Eclipse Chase". 1999-08-05. Retrieved 2010-05-21. On ordinary days, the corona is hidden by the blue sky, since it is about a million times fainter than the layer of the sun we see shining every day, the photosphere. <a href="https://www.sciencedaily.com/releases/1999/08/990805111308.htm" target="_blank">https://www.sciencedaily.com/releases/1999/08/990805111308.htm</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>Lewis, J.S. (2004-02-23). Physics and chemistry of the solar system (Second ed.). Elsevier Academic Press. p. 87. ISBN 978-0-12-446744-6. The dominant color is influenced by the Balmer radiation of atomic hydrogen <a href="978-0-12-446744-6" target="_blank">978-0-12-446744-6</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>Griffin, R.E. (2007-08-27). Hartkopft, W.I.; Guinan, E.F. (eds.). Only Binary Stars Can Help Us Actually SEE a Stellar Chromosphere. Vol. 2 (1 ed.). Cambridge University Press. p. 460. doi:10.1017/S1743921307006163. ISBN 978-0-521-86348-3. S2CID 123028350. {{cite book}}: |journal= ignored (help) <a href="978-0-521-86348-3" target="_blank">978-0-521-86348-3</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> </ol>