|Main article: History of Helium discovery |
Helium was first discovered by two astronomers, the French scientist Pierre Janssen and the English astronomer Norman Lockyer who observed a bright yellow line in the in spectrum of the Sun during the solar eclipse of 1868 (which was named the D3 line). In 1871 Lockyer explained it by the presence of a new element in the Sun. On 26 March 1895 British chemist William Ramsay isolated helium on Earth the gas liberated from the mineral cleveite, in the spectrum of which he noticed a bright-yellow line that matched the D3 line observed in the spectrum of the Sun.
|Main article: Occurrence of Helium |
The abundance of helium on the Earth are estimated as 5x1014m3. In the Earth's crust, the concentration of helium is in 200 bigger than in the atmosphere. The greatest concentrations on the planet are in the depths of the Earth, in the alpha active elements. Helium is a rear and dissipated gas. There are only 0.003 mg of helium in 1 kg of terrestrial matter, in the air is the concentration of helium by volume is only 5.2 parts per million. According to the recent calculations it constitutes 23% of the elemental mass of the universe, while hydrogen is 76 %. All other elements make less than 1% of the space matter! So the matter of universe may be considered as hydrogen-helium constituted. These two elements dominate in stars, planetary nebulae, in interstellar gas.
Almost the entire space helium originated in the first several minutes after the Big Bang, during the initial nucleosynthesis. In the modern Universe almost all new helium is created as a result of the nuclear fusion of hydrogen in stars. On Earth it is created by the radioactive decay of much heavier elements (alpha particles are helium nuclei). After its creation, part of it is trapped with natural gas in concentrations up to 7% by volume.