While observing a solar eclipse in 1868, astronomer Pierre Janssen noticed bright yellow lines in the Sun's chromosphere. He concluded that the chromosphere was gaseous and that it could be studied in the absence of an eclipse. Other astronomers began to study the chromosphere and the yellow lines, including Pierre Lockyer, who measured the wavelength of the lines and realized his findings indicated a previously unknown element. He named the element helium, from the Greek word helios, meaning sun.
While historians credit Janssen and Lockyer with the discovery of helium, Sir William Ramsay, a Scottish chemist, as well as two Swedish chemists who worked independently of Ramsay, Nils Langlet and Per Theodor Cleve, were the first to isolate it in the lab. The researchers treated clevite, an ore containing uranium, with acid to produce helium. Lockyer and other researchers confirmed that the gas produced was a new element when they measured the yellow spectral lines the isolated gas produced when exposed to light. They found that the lines had a wavelength of 587.49 nanometers, which was different than that of other known elemental gases, such as hydrogen.
Although helium only exists in trace amounts on Earth, it is continually produced by the decay of radioactive elements. This decay creates alpha particles, which become helium atoms when they capture electrons.