Coronium

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Coronium was the name of a suggested chemical element, hypothesised in the 19th century. It was named after the solar corona.

During the total solar eclipse of 7 August 1869, a green emission line of wavelength 530.3 nm was observed in the coronal spectrum that did not correspond to any known spectral lines. It was proposed that this was due to an unknown element, provisionally named coronium.

In 1902, in an attempt at a chemical conception of the Aether, Dimitri Mendeleev put forward a hypothesis that there existed two inert chemical elements of lesser atomic weight than hydrogen. Of these two proposed elements, he thought the lighter to be an all-penetrating, all-pervasive gas, and the slightly heavier one to be a proposed element, coronium. Later, he decided to rename it as Newtonium.^[1]

It was not until the 1930s that it was discovered, by Walter Grotrian and Bengt Edlén, 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.