Editing Sun (section)

==== Chromosphere ====
{{Main|Chromosphere}}
Above the temperature minimum layer is a layer about {{val|2000|u=km|fmt=commas}} thick, dominated by a spectrum of emission and absorption lines.<ref name="Abhyankar1977" /> It is called the ''chromosphere'' from the Greek root ''chroma'', meaning colour, because the chromosphere is visible as a coloured flash at the beginning and end of total solar eclipses.<ref name="autogenerated1" /> The temperature of the chromosphere increases gradually with altitude, ranging up to around {{val|20000|u=K|fmt=commas}} near the top.<ref name="Abhyankar1977" /> In the upper part of the chromosphere helium becomes partially [[ionization|ionised]].<ref name="Hansteen1997">{{Cite journal |last1=Hansteen |first1=V. H. |last2=Leer |first2=E. |last3=Holzer |first3=T. E. |date=1997 |title=The role of helium in the outer solar atmosphere |journal=[[The Astrophysical Journal]] |volume=482 |issue=1 |pages=498–509 |bibcode=1997ApJ...482..498H |doi=10.1086/304111 |doi-access=free}}</ref>

[[File:171879main LimbFlareJan12 lg.jpg|thumb|The Sun's transition region taken by [[Hinode (satellite)|Hinode]]'s Solar Optical Telescope|left|alt=A photograph of the surface of the sun, with flares terminating from the surface on the left.]]
The chromosphere and overlying corona are separated by a thin (about {{val|200|u=km}}) transition region where the temperature rises rapidly from around {{val|20000|u=K|fmt=commas}} in the upper chromosphere to coronal temperatures closer to {{val|1000000|u=K|fmt=commas}}.<ref name="Erdelyi2007">{{Cite journal |last1=Erdèlyi |first1=R. |last2=Ballai |first2=I. |date=2007 |title=Heating of the solar and stellar coronae: a review |journal=Astron. Nachr. |volume=328 |issue=8 |pages=726–733 |bibcode=2007AN....328..726E |doi=10.1002/asna.200710803 |doi-access=free}}</ref> The temperature increase is facilitated by the full ionisation of helium in the transition region, which significantly reduces radiative cooling of the plasma.<ref name="Hansteen1997" /> The transition region does not occur at a well-defined altitude, but forms a kind of nimbus around chromospheric features such as [[Solar spicule|spicules]] and [[Solar filament|filaments]], and is in constant, chaotic motion.<ref name="autogenerated1" /> The transition region is not easily visible from Earth's surface, but is readily observable from space by instruments sensitive to [[extreme ultraviolet]].<ref name="Dwivedi2006">{{Cite journal |last=Dwivedi |first=B. N. |date=2006 |title=Our ultraviolet Sun |url=http://www.iisc.ernet.in/currsci/sep102006/587.pdf |url-status=live |journal=[[Current Science]] |volume=91 |issue=5 |pages=587–595 |archive-url=https://web.archive.org/web/20201025001339/http://www.iisc.ernet.in/currsci/sep102006/587.pdf |archive-date=25 October 2020 |access-date=22 March 2015}}</ref>