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18th of August

 

 

 

 

 

 

 

 

 

Aug 18

In 1868 French Astronomer Pierre Janssen became the first person to detect Helium.

 

Helium is the second most abundant element in the Universe (Hydrogen being the most abundant). Most of the Hydrogen was produced at the time if the Big Bang event but millions of tonnes is being constantly produced through the fusion of Hydrogen atoms in the nuclear reactions that power the stars. Despite its huge abundance in the universe helium is quite rare on Earth. It is not that surprising therefore that helium was first detected in the light from the sun before being discovered on earth.

 

Since Isaac Newton in the 17th century scientist have studied the colours produce from light passing through a prism. It was Newton that concluded that these colours were a component of the light and not created by the prism and it was also Newton that gave them the name spectrum. Scientists discovered many things about these lines including William Herschel who found that the red lines produce the most heat while the dark area just beyond that line produced more heat still (the discovery of infrared). William Wollaston was doing a similar experiment when he discovered the presence of black lines within the colours of the spectrum. These lines were later detected by Joseph Von Fraunhofer in 1814 and he continued to work on their origin and the change in the position depending on the light source (the sun, planets and moon). Later work from several other scientist determined that these lines where what we now call absorption lines and can be used to tell us the chemical composition of light sources based on the light frequency the different elements absorb.

 

Helium was first detected by French astronomer Pierre Janssen during a total solar eclipse in Guntur, India on the 18th of August 1868 using spectroscopy. It was evident as a bright yellow line (a wavelength of 587.49 nanometres) in the spectrum of the Chromosphere of the Sun but it was assumed that this line was produced by sodium which produces similar yellow lines. But it was

 

 On the 20th of October 1868 English astronomer Norman Lockyer observed the same line and concluded that it was produced by an element in the sun that was as yet un-discovered on earth. Lockyer and English chemist Edward Frankland named the element after the Greek word for the Sun (helios).

 

 Helium was not isolated on earth until the 26th of March 1895 when a Scottish chemist Sir William Ramsey isolated samples whilst attempting isolate argon. The samples were confirmed to be Helium by Lockyer and English physicist William Crookes. In the same year helium had independently been isolated by Swedish chemists Per Teodor Cleve and Abraham Langle producing enough samples to accurately determine its atomic weight.