In 1864, the English astronomer Sir William Huggins made an amazing discovery. While looking at the Cat’s Eye Nebula through a spectroscope — a device that separates light into its component wavelengths – he observed green lines at wavelengths never seen before. This indicated a new chemical element, which Huggins named Nebulium.
It was an exciting discovery except for one tiny thing – Nebulium didn’t fit anywhere into the periodic table of the elements. But the periodic table had just been created (and was, in fact, erroneous in several respects), and the discovery of chemical elements was still in its infancy.
On August 18, 1868 – barely four years after Huggins’ discovery — French astronomer Pierre Jules César Janssen and English astronomer Joseph Norman Lockyer independently found another new element while looking through their spectroscopes during a total eclipse of the sun.
Janssen and Lokyer determined that a line of yellow everyone had assumed to be sodium didn’t match up to the wavelength of any known element. Lockyer named this new element “helium.” Unlike nebulium, however, helium fit cleanly into the periodic table — though it would be another 27 years before Sir William Ramsay, a Nobel prize-winning chemist, would discover helium on earth (along with the next four noble gases, argon, neon, krypton, and xenon).
In the meantime, nebulium hung in there as the Schrödinger’s Cat of elements, both existing and not existing at the same time. Only in 1927 did Caltech physicist Ira Bowen determine that nebulium was nothing more than doubly ionized oxygen, which was able to exist in the excited state of a nebula, but not on earth.