The Eclipse That Led to Helium
Next: August 18, 2027
A yellow line in sunlight.
The story
Where it comes from
This Story marks 18 August 1868, when a total eclipse of the Sun crossed India and astronomers turned a new instrument, the spectroscope, on the glowing prominences at the Sun's edge. At Guntur the French astronomer Jules Janssen saw a bright yellow line among their colours, and at Masulipatam the British astronomer Norman Pogson noted one close to the line of sodium. It came from an element then unknown on Earth. The English astronomer Norman Lockyer studied the line that autumn, and the element was named helium, from helios, Greek for the Sun.
How it's celebrated
There is no formal observance. Popular accounts often say Janssen discovered helium that day, but historians point out that he never claimed a new element, and credit is still argued over. Helium was found on Earth only in 1895, when the chemist William Ramsay saw the same yellow line in gas from a uranium mineral. A party balloon is a fine reminder of the day: the gas inside it was found in sunlight first.
Did you know
- After the eclipse, Janssen worked out in India how to see the prominences without one; Lockyer found the same method in England, and their reports reached the French Academy of Sciences on the same day.
- During the same eclipse, Pogson also spotted a green line in the Sun's corona, long before the American astronomer Charles Young, who usually gets the credit.
- Helium is the second most abundant element in the observable universe, yet it is rare on Earth.
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