Helium was first identified in the Sun's spectrum before it was found on Earth.
During a total solar eclipse in 1868, astronomers observed an unfamiliar yellow spectral line in sunlight. They concluded that the line came from an unknown element and named it helium, from Helios, the Greek god of the Sun. This made helium the first element discovered through astronomical observation rather than terrestrial minerals.
Helium was later detected on Earth in 1895, when British chemist William Ramsay examined the uranium mineral cleveite. The gas had the same distinctive spectral signature as the mysterious solar element. Its atomic number is 2, and it is the second-lightest element after hydrogen.
The discovery story is sometimes simplified as saying helium was found only in the Sun. In fact, spectroscopy revealed it in sunlight first, while its terrestrial discovery came decades later. Helium is now widely used in cryogenics, leak detection, balloons and some medical technologies.