Editing X-ray astronomy (section)

====Coronal mass ejection====
A [[coronal mass ejection]] (CME) is an ejected plasma consisting primarily of electrons and [[proton]]s (in addition to small quantities of heavier elements such as helium, oxygen, and iron), plus the entraining coronal closed magnetic field regions. Evolution of these closed magnetic structures in response to various photospheric motions over different time scales (convection, differential rotation, meridional circulation) somehow leads to the CME.<ref name=Gopalswamy>{{Cite journal|author=Gopalswamy N|author2=Mikic Z|author3=Maia D|author4=Alexander D|author5=Cremades H|author6=Kaufmann P|author7=Tripathi D|author8= Wang YM |title=The pre-CME Sun |journal=Space Science Reviews|date=2006 |volume=123|issue=1–3 |page=303|doi=10.1007/s11214-006-9020-2|bibcode = 2006SSRv..123..303G |s2cid=119043472 }}</ref> Small-scale energetic signatures such as plasma heating (observed as compact soft X-ray brightening) may be indicative of impending CMEs.

The soft X-ray sigmoid (an S-shaped intensity of soft X-rays) is an observational manifestation of the connection between coronal structure and CME production.<ref name=Gopalswamy/> "Relating the sigmoids at X-ray (and other) wavelengths to magnetic structures and current systems in the solar atmosphere is the key to understanding their relationship to CMEs."<ref name=Gopalswamy/>

The first detection of a Coronal mass ejection (CME) as such was made on December 1, 1971, by R. Tousey of the US Naval Research Laboratory using [[OSO 7]].<ref name=Howard>{{cite web|title=R.A.Howard, A Historical Perspective on Coronal Mass Ejections |url=http://hesperia.gsfc.nasa.gov/summerschool/lectures/vourlidas/AV_intro2CMEs/additional%20material/corona_history.pdf |archive-url=https://web.archive.org/web/20061012002045/http://hesperia.gsfc.nasa.gov/summerschool/lectures/vourlidas/AV_intro2CMEs/additional%20material/corona_history.pdf |archive-date=2006-10-12 |url-status=live}}</ref> Earlier observations of '''coronal transients''' or even phenomena observed visually during [[solar eclipses]] are now understood as essentially the same thing.

The largest geomagnetic perturbation, resulting presumably from a "prehistoric" CME, coincided with the first-observed solar flare, in 1859. The flare was observed visually by [[Richard Christopher Carrington]] and the [[geomagnetic storm]] was observed with the recording magnetograph at [[Kew Gardens]]. The same instrument recorded a '''crotchet''', an instantaneous perturbation of the Earth's ionosphere by ionizing soft X-rays. This could not easily be understood at the time because it predated the discovery of X-rays (by [[Wilhelm Conrad Roentgen|Roentgen]]) and the recognition of the [[ionosphere]] (by [[Arthur Edwin Kennelly|Kennelly]] and [[Heaviside]]).