February 22, 1824 - Birth of Pierre Janssen, discoverer of the chemical element helium

Pierre Jules César Janssen graduated in mathematics from the University of Paris and devoted himself to teaching and research.

He also undertook several scientific missions, one of the most important of which was to Guntur in India. The purpose of this mission was to study the total solar eclipse that occurred on 18 August 1868. In this way, he was able to demonstrate the gaseous nature of the prominences and red flames of the Sun. To do this he devised a method of observing them under ordinary daylight conditions without the use of eclipses. One of the main objectives of his spectroscopic investigations was to answer the question of whether the Sun contains oxygen or not.

During the experiment, he observed a bright yellow line with a wavelength of 587.49 nanometres in the spectrum of the Sun's chromosphere, indicating the existence of an unknown element. When he reported this fact, he was ridiculed, as no element had ever been detected in space before it was found on Earth. On 20 October of the same year, the English astronomer Lockyer also observed the same yellow line in the solar spectrum and concluded that it was caused by an unknown element after he unsuccessfully tried to prove that it was a certain type of hydrogen. He later proved that it was a hitherto new element: helium. Janssen was therefore its discoverer.

If you want to know more about this scientist, click on the following link: Pierre Janssen