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The eclipse of Helium gas in 1868

The helium was discovered in the Sun's atmosphere in the occasion of a solar eclipse in 1868.

German physicist Gustav Kirchhoff discovered in 1859  how the light of the sun or the stars reveal their chemical composition and created the spectroscope and founded the science of spectroscopy. It was the first solar eclipse after Kirchhoff's  discovery where astronomers have tried to determine the chemical composition of the solar atmosphere and the prominences - bright purple flames that can be seen at the eclipse - by attaching the spectroscope to the telescope.

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The path of totality crossing India of solar eclipse on 18 August, 1868

French astronomer Pierre Jules César Janssen camped out in Guntoor, India, to watch the eclipse at 18 August, 1868. Using his spectroscope Janssen discovered that the prominences were mostly made of super-hot hydrogen gas. But he also noticed something extra: Using a special prism instrument called a spectroscope, he determined that the line of yellow light everyone had assumed to be sodium didn’t match up to the wavelength of any known element. Janssen was so impressed by the brightness of the sun’s emission lines that he felt sure they could be seen without an eclipse, if he could just figure out how to block other wavelengths of visible light. Working feverishly over the next few weeks, Janssen built the first “spectrohelioscope”.total1868 close

 

Unbeknownst to Janssen, a second scientist was also working on the same problem 5,000 miles away. English astronomer Joseph Norman Lockyer succeeded in viewing the solar prominences in regular daylight in October 1868. In stunning scientific synchronicity, the two scientists’ papers arrived at the French Academy of Sciences on the same day, and today both men are credited with the first sighting of  - as this element is named today - the helium.

 

 Janssen's observing place with data of eclipse.

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The Paris Mint made a commemorative medal in memory of the discovery. The designer artist was ALPHEE Dubois. On obverse the radiating crowned sun god Helios in a four-horse chariot, Quadriga with his right hand points to the Moon hides the Sun with clearly visible prominences in its atmosphere. Under the Sun is the zodiac with the sign of Lion, while behind Helios Virgo is pictured. The French legend "ANALYSE DES PROTUBERANCES SOLAIRES . 18 AOUT 1868." that is, the observation of solar prominences and the exact date of the eclipse.

The reverse shows the portrait of the two scientists at the right, in legend are their names.