Topic summary
Sun's corona
Extracted from the Wikipedia article Solar corona.
Observational history
The high temperature of the Sun's corona gives it unusual 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 ionizediron (Fe-XIV, or Fe). 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 at 5303Å, but also the red Fe-X line from Fe at 6374Å).