Why Helium was the Dark Matter of its Day

Why Helium was the Dark Matter of its Day: In the middle of the 1800s, scientists couldn't stop puzzling over the strange data that they kept finding. When they looked at the sun and at other stars through spectroscopes, they found a funny line, a frequency of light that was emitting by something, but not by any element that they had gotten their hands on yet. This was not a negligible trace of plasma or whiff of gas. This was a full twenty-four percent of the mass of stars in the galaxy. Because it seemed a solely stellar element, in 1868 it was named 'helium,' after Helios, the sun god. It was clearly a massive chunk of the universe of which we were a part, but no one could get their hands on it.