The story of helium, a colorless, inert gas with the atomic number two, is unique because its discovery began not on Earth, but in the atmosphere of the Sun. Determining who truly discovered it is complicated, as the process involved two distinct phases: initial observation from afar and subsequent isolation on our planet. This decades-long journey required the innovative use of spectroscopy to bridge celestial observation and terrestrial chemistry.
The First Glimpse: Discovery by Solar Observation
The first indication of helium’s existence occurred during a total solar eclipse in India on August 18, 1868. French astronomer Pierre Janssen used a spectroscope to analyze light from the Sun’s chromosphere, the layer of gas just above the surface. Janssen observed a bright yellow spectral line that did not match the known signature of any element on Earth. This novel line, which he realized could be observed even without an eclipse, marked the first sighting of the element.
Coincidentally, English astronomer Joseph Norman Lockyer independently observed the same spectral line two months later from Britain. Recognizing the significance of the unidentified signature, Lockyer was the first to hypothesize that the line represented a new element present in the Sun. He and his colleague, chemist Edward Frankland, designated the line as D3, distinguishing it from the D1 and D2 lines belonging to sodium.
Lockyer and Frankland named the hypothetical element “Helium,” deriving it from the Greek word for the Sun, Helios. This celestial naming proposed the existence of an element based solely on its spectral fingerprint in a star. This identification demonstrated the power of spectroscopy as a tool for chemical analysis across vast cosmic distances.
Isolating the Element on Earth
For nearly three decades, helium remained a purely theoretical element, known only through its distinct yellow light emission from the Sun. The breakthrough in isolating it came in 1895 through the work of Scottish chemist Sir William Ramsay. Ramsay was investigating the gas released from cleveite, a radioactive mineral, while initially searching for the noble gas argon.
Ramsay treated the cleveite mineral with mineral acids, causing the mineral to disintegrate and release a gas. After meticulously removing all known gases, he examined the spectrum of the remaining gas. To his surprise, the gas produced the exact bright yellow D3 spectral line that had been observed in the Sun decades earlier.
Ramsay’s spectroscopic confirmation proved that the celestial element, helium, was also present on Earth, trapped within radioactive minerals. The same year, Swedish chemists Per Teodor Cleve and Abraham Langlet independently isolated the gas from cleveite, confirming Ramsay’s findings. This terrestrial isolation completed the element’s discovery, allowing for the accurate determination of its atomic weight and placement in the periodic table as a noble gas.
The Significance of a Celestial Discovery
The discovery of helium holds a unique place in scientific history because it was the first element identified in an extraterrestrial body before being chemically isolated on Earth. This finding validated astronomical spectroscopy, confirming that light carries precise chemical information about distant celestial objects. The success demonstrated that the laws of physics and chemistry apply uniformly across the universe, a foundational concept for modern science.
The initial identification of helium paved the way for the development of astrophysics, allowing scientists to understand the composition and internal workings of stars. Previously, determining the chemical makeup of the Sun without physically sampling it was considered speculative. Helium’s story is a testament to the power of observation and scientific deduction, connecting the laboratory bench to the cosmos.