It’s a rather peculiar tale in the annals of science, a story where an element was spotted in the fiery heart of our solar system, the Sun, a full quarter-century before anyone stumbled upon it here on our own planet. This isn’t the usual order of things. Typically, we identify substances in our terrestrial laboratories and then, perhaps, train our instruments skyward to find them in the cosmos. But helium, the second most abundant element in the universe, decided to make its grand entrance from a stage 93 million miles away.
A Solar Spectacle and an Unexpected Line
The year was 1868. Astronomers worldwide were abuzz with excitement for a total solar eclipse, a celestial event that provides a rare opportunity to study the Sun’s outer atmosphere, its corona and chromosphere, normally obscured by the star’s intense glare. Among those keenly anticipating the event was French astronomer Pierre Jules César Janssen. He traveled all the way to Guntur in India, armed with a spectroscope, an instrument that splits light into its constituent colors, revealing a spectrum interspersed with dark or bright lines. These lines are like elemental fingerprints, unique to each substance.
On August 18th, 1868, as the Moon slid perfectly in front of the Sun, Janssen aimed his spectroscope at the solar prominences – those magnificent reddish gas ejections leaping from the Sun’s surface. He observed the expected bright spectral lines of hydrogen. But then, he saw something else, something unexpected: a brilliant yellow line very close to the sodium D lines, but distinct. He meticulously recorded its wavelength at 587.49 nanometers. So profound was his observation, and so clear were the prominences even after the eclipse ended, that Janssen realized he could study them in broad daylight, a revolutionary idea at the time.
Unbeknownst to Janssen, across the English Channel, another astronomer, Norman Lockyer, was also pioneering the technique of observing solar prominences without an eclipse. On October 20th, 1868, Lockyer, too, observed this same mysterious yellow line in the solar spectrum. He, like Janssen, concluded that this line did not correspond to any element known on Earth at the time. His conviction was so strong that he proposed it belonged to a new, undiscovered element, unique to the Sun.
Both Pierre Janssen and Norman Lockyer independently observed a new, bright yellow spectral line in the Sun’s chromosphere during 1868. This line, with a wavelength of 587.49 nanometers, did not match any known terrestrial element. Their simultaneous discoveries, announced to the French Academy of Sciences on the same day, highlighted the power of spectroscopy in astronomical research.
Lockyer, in collaboration with the chemist Edward Frankland, took the bold step of naming this hypothetical solar element. They derived the name from the Greek word for the Sun, “helios,” dubbing it helium. This was a significant departure from convention, naming an element based solely on astronomical observation before any physical sample had been isolated or studied in a laboratory.
The Skeptical Scientific Community
The idea of an element existing on the Sun but not on Earth was met with considerable skepticism by many in the scientific community. It was a radical notion. For decades, the nature of this “helium” remained a subject of debate. Some scientists wondered if it was perhaps a form of hydrogen under unusual solar conditions, or an altogether different phenomenon. The evidence was purely spectral, a line of light from a distant star, and direct physical proof was, for the time being, impossible to obtain from the Sun itself.
Janssen and Lockyer, however, remained confident in their findings. Lockyer, in particular, continued to champion the existence of helium, publishing further research and arguing for its elemental nature. The scientific method, though, demands rigorous proof, and the astronomical evidence, while compelling, wasn’t enough to fully convince everyone without a terrestrial counterpart.
Helium Makes Its Earthly Debut
The mystery of helium lingered for over two decades. Then, in 1895, the scene shifted from astronomical observatories to the chemistry laboratory. Scottish chemist Sir William Ramsay, already famous for his discovery of argon (another noble gas) a year earlier, was investigating a uranium-bearing mineral called cleveite. It was known that when cleveite was treated with acids, it produced a gas. The initial assumption was that this gas was nitrogen or argon.
Ramsay, however, was meticulous. He collected the gas emitted from the cleveite and subjected it to spectroscopic analysis. To his astonishment, after removing nitrogen and argon, he observed a spectrum that featured a brilliant, unfamiliar yellow line. He, along with his colleagues William Crookes and Norman Lockyer (who was sent a sample), confirmed that this yellow line was identical to the one observed in the solar spectrum by Janssen and Lockyer 27 years prior. The solar element had finally been found on Earth!
Sir William Ramsay’s 1895 experiment with the mineral cleveite was a landmark. He isolated a gas that, when analyzed spectroscopically, showed the same unique yellow line observed in the Sun. This discovery irrefutably proved that helium existed on Earth, vindicating Janssen and Lockyer’s earlier solar observations and conclusions. It was a pivotal moment confirming the elemental nature of helium.
This was a triumphant moment for science. It not only confirmed the existence of a new element but also validated the power of spectroscopy as a tool for discovery, bridging the vast distances of space. Almost simultaneously, and independently, Swedish chemists Per Teodor Cleve and Nils Abraham Langlet also isolated helium from cleveite in Uppsala, Sweden, further corroborating Ramsay’s findings.
The Significance of the Discovery
The discovery of helium, first in the Sun and then on Earth, had profound implications.
- Composition of Stars: It provided direct evidence that the Sun was made of elements that, even if not yet found, could exist on Earth. It opened the door to understanding stellar composition in a more concrete way.
- Spectroscopy Vindicated: It was a stunning validation of astrophysical spectroscopy. A mere line of light from the Sun had accurately predicted the existence and a key characteristic of an element before it was physically handled.
- A New Class of Elements: Helium turned out to be the first of the noble gases to be identified via its spectrum, though argon was isolated first. It’s incredibly inert, meaning it doesn’t readily react with other elements. This property explains why it took so long to find on Earth; it wasn’t hiding in common compounds.
- Understanding the Universe: We now know helium is the second most abundant element in the universe, forged in the Big Bang and in the hearts of stars through nuclear fusion. Its discovery story is a key chapter in our understanding of the cosmos.
The unique circumstances of helium’s discovery – a celestial find preceding a terrestrial one – underscore a fundamental truth: the universe is a vast laboratory, and the elements that make up our world are also the building blocks of distant stars and galaxies. The bright yellow line observed by Janssen and Lockyer was more than just a scientific curiosity; it was a messenger from the Sun, carrying news of a new substance that would eventually find myriad uses on Earth, from lifting balloons and airships (due to its lightness and non-flammability) to cooling superconducting magnets in advanced scientific instruments, and even in specialized welding processes due to its inert atmosphere.
It’s a testament to the power of observation, the courage to propose new ideas against prevailing skepticism, and the interconnectedness of the cosmos. The Sun, our life-giving star, not only illuminates our world but also, in this instance, illuminated a new corner of the periodic table before we even knew to look for it under our own feet. The story of helium remains a shining example of scientific discovery unfolding in unexpected and fascinating ways, a cosmic “hello” from an element that waited patiently in the Sun to be noticed, reminding us that there are still wonders to be found, both on our world and far beyond.
