Helium was discovered on the Sun nearly 30 years before it was found on Earth.

The discovery of helium began during the solar eclipse of August 18, 1868. French astronomer Pierre Janssen and English astronomer Norman Lockyer independently observed a bright yellow line in the solar spectrum that did not match sodium or any other known element. Lockyer concluded it was a new element and named it after Helios, the Greek personification of the Sun.For decades, many scientists believed this "solar element" might exist only under the extreme temperatures and pressures of the Sun. It remained a celestial mystery until 1895, when Scottish chemist Sir William Ramsay was searching for argon. He treated a mineral called cleveite with mineral acids and isolated a gas that produced the same distinctive yellow spectral line observed years earlier.This discovery proved that helium was a terrestrial element, not merely a solar phenomenon. Around the same time, independent of Ramsay, Swedish chemists Per Teodor Cleve and Abraham Langlet also successfully isolated the gas and determined its atomic weight. This 27-year gap between solar and terrestrial discovery is unique in the history of the periodic table.Helium is the second most abundant element in the universe, yet it is relatively rare on Earth because it is light enough to escape into space. Most of the helium we use today is actually a byproduct of the radioactive decay of heavy elements like uranium and thorium. It becomes trapped in natural gas deposits deep underground, where it is eventually extracted for industrial use.