Editing Aurora (section)

=== Colours and wavelengths of auroral light ===

* Red: At its highest altitudes, [[Excited state|excited]] atomic oxygen emits at 630&nbsp;nm (red); low concentration of atoms and lower sensitivity of eyes at this wavelength make this colour visible only under more intense solar activity. The low number of oxygen atoms and their gradually diminishing concentration is responsible for the faint appearance of the top parts of the "curtains". Scarlet, crimson, and carmine are the most often seen hues of red for the auroras.<ref>{{Cite web |title=The Colors of the Aurora (U.S. National Park Service) |url=https://www.nps.gov/articles/-articles-aps-v8-i1-c9.htm |access-date=2025-05-19 |website=www.nps.gov |language=en}}</ref>
* Green: At lower altitudes, the more frequent collisions suppress the 630&nbsp;nm (red) mode: rather the 557.7&nbsp;nm emission (green) dominates. A fairly high concentration of atomic oxygen and higher eye sensitivity in green make green auroras the most common. The excited molecular nitrogen (atomic nitrogen being rare due to the high stability of the N<sub>2</sub> molecule) plays a role here, as it can transfer energy by collision with an oxygen atom, which then radiates it away at the green wavelength. (Red and green can also mix together to produce pink or yellow hues.) The rapid decrease in concentration of atomic oxygen below about 100&nbsp;km is responsible for the abrupt-looking end of the lower edges of the curtains. Both the 557.7 and 630.0&nbsp;nm wavelengths correspond to [[forbidden transition]]s of atomic oxygen, a slow mechanism responsible for the graduality (0.7&nbsp;s and 107&nbsp;s respectively) of flaring and fading.<ref>{{Cite web |title=The Colors of the Aurora (U.S. National Park Service) |url=https://www.nps.gov/articles/-articles-aps-v8-i1-c9.htm |access-date=2025-05-19 |website=www.nps.gov |language=en}}</ref>
[[File:AuroraBorealisOkeford20240510-01.jpg|thumb|2024 appearance seen in England radiating blue through red aurora]] 
* Blue: At yet lower altitudes, atomic oxygen is uncommon, and molecular nitrogen and ionized molecular nitrogen take over in producing visible light emission, radiating at a large number of wavelengths in both red and blue parts of the spectrum, with 428&nbsp;nm (blue) being dominant. Blue and purple emissions, typically at the lower edges of the "curtains", show up at the highest levels of solar activity.<ref>{{cite web|work=Windows to the Universe|title=Auroral colors and spectra|url=http://www.windows2universe.org/earth/Magnetosphere/tour/tour_earth_magnetosphere_09.html|access-date=13 January 2014|archive-date=19 December 2014|archive-url=https://web.archive.org/web/20141219143402/http://www.windows2universe.org/earth/Magnetosphere/tour/tour_earth_magnetosphere_09.html|url-status=live}}</ref> The molecular nitrogen transitions are much faster than the atomic oxygen ones.
* Ultraviolet: Ultraviolet radiation from auroras (within the optical window but not visible to the human eye) has been observed with the requisite equipment. Ultraviolet auroras have also been seen on Mars,<ref name="scinewscom">{{cite web|url=http://www.sci-news.com/space/science-nasas-maven-ultraviolet-aurora-mars-02614.html|title=NASA's MAVEN Orbiter Detects Ultraviolet Aurora on Mars &#124; Space Exploration|publisher=Sci-News.com|access-date=16 August 2015|archive-date=25 July 2015|archive-url=https://web.archive.org/web/20150725140509/http://www.sci-news.com/space/science-nasas-maven-ultraviolet-aurora-mars-02614.html|url-status=live}}</ref> Jupiter, and Saturn.
* Infrared: Infrared radiation, in wavelengths that are within the optical window, is also part of many auroras.<ref name="scinewscom" /><ref>{{cite web|url=http://www.dapep.org/DAPT/EM-Wiki/aurora-borealis.html|title=Aurora Borealis|publisher=dapep.org|access-date=16 August 2015|archive-date=19 April 2015|archive-url=https://web.archive.org/web/20150419140349/http://www.dapep.org/DAPT/EM-Wiki/aurora-borealis.html|url-status=dead}}{{clarify|reason=dapep.org is down. Cite by name, not domain name. What was it – possibly Denver Area Physics Education Project?|date=November 2023}}</ref>
* Yellow and pink are [[Additive colour|a mix]] of red and green or blue. Yellow and pink auroras are relatively rare and are associated with high solar activity.<ref>{{Cite web |last=updated |first=Daisy Dobrijevic last |date=23 June 2023 |title=Aurora colors: What causes them and why do they vary? |url=https://www.space.com/aurora-colors-explained |access-date=31 March 2025 |website=Space.com |language=en}}</ref> Other shades of red, as well as orange and gold, also may be seen on rare occasions. As red, green, and blue are linearly independent colours, additive synthesis could, in theory, produce most human-perceived colours, but the ones mentioned in this article comprise a virtually exhaustive list.