How Scientists Discovered Helium, the First Alien Element, 150 Years Ago

First found only on the sun, scientists doubted the mysterious element even existed for more than a decade

By Lorraine Boissoneault
SMITHSONIAN.COM
AUGUST 17, 2018 8:00AM

“I have obtained one of the finest and least expected results—Spectra of the stars!—and beautiful spectra with colors and magnificent lines. Just one more step and the chemical composition of the universe will be revealed,” wrote astrophysicist Pierre Jules César Janssen to his wife from an observatory in Italy in December 1862. Armed with the latest technology of the day and observations made by other Western astrophysicists, Janssen was determined to pry open the secrets of the galaxy.

On August 18, 1868, Janssen managed to do just that. He became the first person to observe helium, an element never before seen on Earth, in the solar spectrum. At the time, though, Janssen didn’t know what he’d seen—just that it was something new.

The mid-1800s was an exciting time to peer at the heavens. A new instrument called a spectroscope was upending the field of astronomy. Similar in design to a telescope, the spectroscope worked like a super-powered prism, dispersing light into measurable wavelengths. An early model had allowed physicist Joseph Fraunhofer to observe the sun in the early 1800s, but he was puzzled by black lines interrupting the normal colors. These black lines were named for Fraunhofer, even though he didn’t understand what they were.

That knowledge would come several decades later, with German researchers Gustav Kirchhoff and Robert Bunsen. In 1859, Bunsen and Kirchoff discovered that heating different elements produced bright lines of light in the spectroscope—and those lines of light sometimes corresponded to the dark Fraunhofer lines.

Read more: https://www.smithsonianmag.com/history/how-scientists-discovered-helium-first-alien-element-1868-180970057/#Ap1zKHyDWmI3CceI.99