Tuesday, August 18, 2009

Helium Discovered 141 Years Ago Today

"Aug. 18, 1868: Helium Discovered During Total Solar Eclipse"
This Day in Tech, Wired (August 17, 2009)

"1868: A French astronomer spots an unknown element, now known as helium, in the spectrum of the sun during a much-anticipated total eclipse. The event marks the first discovery of an 'extraterrestrial' element, as helium had not yet been found on Earth.

"Astronomers had been eagerly awaiting a total solar eclipse since 1859, when German physicist Gustav Kirchhoff figured out how to use the analysis of light to deduce the chemical composition of the sun and the stars. Scientists wanted to study the bright red flames that appeared to shoot out from the sun, now known to be dense clouds of gas called solar prominences. But until 1868, they thought the sun’s spectrum could only be observed during an eclipse.

"French astronomer Pierre Jules César Janssen camped out in Guntoor, India ... 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...."

We've filled in the periodic table through element 112, and are studying elements 114, 116, and 118 - although 116 and 118 haven't been completely nailed down - which isn't the way physicists put it. For that matter, there are some fairly basic characteristics of 114 that are unknown: like its atomic weight and electron configuration.

The Wired article is a pretty good overview (I use that phrase a lot, don't I?) of how helium was discovered, and the scientist who found the new element. Newly-discovered, that is.

If cosmologists are anywhere near correct, helium has been around almost as long as the universe has. Which is another topic.

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