During the total solar eclipse of 7 August 1869, a green emission line of wavelength 530.3 nm was independently observed by Charles Augustus Young (1834–1908) and William Harkness (1837–1903) in the coronal spectrum.
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It was not until the 1930s that Walter Grotrian and Bengt Edlén discovered that the spectral line at 530.3 nm was due to highly ionized iron (Fe13+); other unusual lines in the coronal spectrum were also caused by highly-charged ions, such as nickel, the high ionization being due to the extreme temperature of the solar corona.