Editing Sun (section)

== Atmosphere ==
Five layers make up the [[atmosphere]] of the Sun. The [[chromosphere]], transition region, and [[corona]] are much hotter than the outer photosphere surface of the Sun.<ref name=Abhyankar1977/> It is believed that [[Alfvén wave]]s may pass through to heat the corona.<ref>
{{Cite journal|last=De Pontieu B. |display-authors = etal|title=Chromospheric Alfvénic waves strong enough to power the solar wind|url=https://archive.org/details/sim_science_2007-12-07_318_5856/page/1574 |journal=Science|volume=318 |issue=5856 |pages=1574–77|year=2007|doi=10.1126/science.1151747|pmid=18063784|bibcode = 2007Sci...318.1574D |s2cid = 33655095}}</ref>

The '''minimum temperature zone''', the coolest layer of the Sun, is about {{convert|500|km|abbr=off}} above the photosphere. It has a temperature of about {{cvt|4100|K}}.<ref name=Abhyankar1977>{{Cite journal|last=Abhyankar K.D.|title=A survey of the solar atmospheric models|year=1977|journal=Bull. Astr. Soc. India|volume=5|bibcode=1977BASI....5...40A|pages=40–44|url=http://prints.iiap.res.in/handle/2248/510}}</ref> This part of the Sun is cool enough to allow simple molecules such as [[carbon monoxide]] and water to form. These molecules can be seen on the Sun with special instruments called [[Spectroscope|spectroscopes]].<ref name=Solanki1994>{{Cite journal|last=Solanki S.K; Livingston W. & Ayres T|title=New light on the heart of darkness of the solar chromosphere |url=https://archive.org/details/sim_science_1994-01-07_263_5143/page/64|year=1994|journal=Science|pmid=17748350|volume=263|issue=5143|pages=64–66|doi=10.1126/science.263.5143.64|bibcode = 1994Sci...263...64S |s2cid=27696504 }}</ref>

The '''chromosphere''' is the first layer of the Sun which can be seen, especially during a [[solar eclipse]] when the moon is covering most of the Sun and blocking the brightest light.

The '''solar transition region''' is the part of the Sun's atmosphere, between the chromosphere and outer part called the [[corona]].<ref name=MSFC>{{cite web|title=The Transition Region|url=http://solarscience.msfc.nasa.gov/t_region.shtml|work=Solar Physics, NASA Marshall Space Flight Center|publisher=NASA|access-date=2012-12-12|archive-date=2017-01-08|archive-url=https://web.archive.org/web/20170108211927/https://solarscience.msfc.nasa.gov/t_region.shtml|url-status=dead}}</ref>  It can be seen from [[outer space|space]] using telescopes that can sense [[ultraviolet]] light. The transition is between two very different layers. In the bottom part it touches the photosphere and gravity shapes the features. At the top, the transition layer touches the corona.

The '''[[corona]]''' is the outer atmosphere of the Sun and is much bigger than the rest of the Sun. The corona continuously expands into space forming the [[solar wind]], which fills all the Solar System.<ref name=Russell2001/> The average temperature of the corona and solar wind is about {{cvt|1000000|–|2000000|K|F}}. In the hottest regions it is {{cvt|8000000|–|20000000|K|F}}.<ref name=Erdelyi2007/> We do not understand why the corona is so hot.<ref name=Russell2001>{{Cite book|last=Russell|first=C.T.|title=Space weather (Geophysical Monograph)|year=2001|publisher=American Geophysical Union|chapter=Solar wind and interplanetary magnetic filed: A tutorial|editor=Song, Paul; Singer, Howard J. and Siscoe, George L.|isbn=978-0-87590-984-4|pages=73–88|url=http://www-ssc.igpp.ucla.edu/personnel/russell/papers/SolWindTutorial.pdf|access-date=2012-12-12|archive-date=2018-10-01|archive-url=https://web.archive.org/web/20181001131951/http://www-ssc.igpp.ucla.edu/personnel/russell/papers/SolWindTutorial.pdf|url-status=dead}}</ref><ref name=Erdelyi2007>Erdèlyi R. & Ballai I. 2007. Heating of the solar and stellar coronae: a review. ''Astron. Nachr''. '''328''' (8): 726–733</ref> It can be seen during a [[solar eclipse]] or with an instrument called a [[coronagraph]].

The '''[[heliosphere]]''' is the thin outer atmosphere of the Sun, filled with the [[solar wind]] [[Plasma (physics)|plasma]]. It extends out past the orbit of [[Pluto]] to the [[Heliopause (astronomy)|heliopause]], where it forms a boundary where it collides with the [[interstellar medium]].<ref>{{cite press release
 |url=http://www.spaceref.com/news/viewpr.html?pid=16394
 |title=The distortion of the Heliosphere: our interstellar magnetic compass
 |year=2005
 |publisher=[[European Space Agency]]
 |accessdate=2006-03-22
 |archive-date=2020-05-11
 |archive-url=https://web.archive.org/web/20200511052656/http://www.spaceref.com/news/viewpr.html?pid=16394
 |url-status=dead
 }}</ref>