Editing Stellar corona (section)

=== Historical theories ===

The high temperature of the Sun's corona gives it unusual [[spectroscopy|spectral]] features, which led some in the 19th century to suggest that it contained a previously unknown element, "[[coronium]]". Instead, these spectral features have since been explained by [[highly charged ion|highly ionized]] [[iron]] (Fe-XIV, or Fe<sup>13+</sup>).  [[Bengt Edlén]], following the work of [[Walter Grotrian]] in 1939, first identified the coronal spectral lines in 1940 (observed since 1869) as transitions from low-lying [[metastable]] levels of the ground configuration of highly ionised metals (the green Fe-XIV line from Fe<sup>13+</sup> at {{gaps|5|303|[[Ångström|Å]]}}, but also the red Fe-X line from Fe<sup>9+</sup> at {{gaps|6|374|Å}}).<ref name="Aschwanden" />