In 1868, an eclipse in India revealed an element found on Earth 27 years later
During the 1868 solar eclipse in India, astronomers observed a mysterious yellow spectral line in the Sun's light that was later identified as helium. This discovery demonstrated how solar eclipses serve as natural laboratories for identifying elements before they are found on Earth.
Why it matters
This historical event illustrates the importance of astronomical observation in the development of modern chemistry and physics.
In August 1868, the Sun briefly became a laboratory for astronomers gathered in India to watch a total solar eclipse. Among them was the French astronomer Pierre Jules Janssen, who turned a spectroscope towards the bright prominences rising around the eclipsed solar disc. Their light contained a yellow spectral line that seemed to sit close to the familiar sodium lines, yet did not quite match them. At the time, nobody could say what produced it. The observation would eventually be linked to helium, an element that was then unknown on Earth. But the story is slightly different from the familiar version.
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