At first it was hypothesized that the line might be due to an unknown element, which was named nebulium—a similar idea had led to the discovery of helium through analysis of the Sun's spectrum in 1868.
La început s-a lansat ipoteza că linia s-ar datora unui element necunoscut care a fost denumit nebulium - o idee similară a dus la descoperirea heliului prin analiza spectrală a Soarelui în 1868.