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.
Nun principio apareceu a hipótese de que a liña podería deberse a un elemento descoñecido, que foi bautizado como nebulium (unha idea semellante levou ao descubrimento do helio pola análise do espectro do Sol en 1868).