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Helium (from Greek: ἥλιος, romanized: helios, lit. 'sun') is a chemical element; it has symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table.
Helium is produced as a side product. Previously, Onnes obtained helium from processing monazite, and Onnes used the processed monazite (which still contained thorium) to trade for the helium. On earth, helium is usually found in coexistence with radioactive material, since it is a product of radioactive decay. [6]
An observation of the new yellow line had been made earlier by Janssen at the 18 August 1868 solar eclipse [13], and because their papers reached the French academy on the same day, he and Lockyer usually are awarded joint credit for helium's discovery. Terrestrial helium was found about 27 years later by the Scottish chemist William Ramsay.
Pierre Janssen and Joseph Norman Lockyer had discovered a new element on 18 August 1868 while looking at the chromosphere of the Sun, and named it helium after the Greek word for the Sun, ἥλιος (hḗlios). [9] No chemical analysis was possible at the time, but helium was later found to be a noble gas.
Jules Janssen; photograph by Nadar (date unknown) Photo taken by Janssen, from the Meudon observatory, of Renard and Krebs' La France dirigible (1885). Pierre Jules César Janssen (22 February 1824 – 23 December 1907), usually known as Jules Janssen, was a French astronomer who, along with English scientist Joseph Norman Lockyer, is credited with discovering the gaseous nature of the solar ...
The tail is a region where the Sun's solar wind slows down and ultimately escapes the heliosphere, slowly evaporating because of charge exchange. [42] The shape of the heliotail (newly found by NASA's Interstellar Boundary Explorer – IBEX), is that of a four-leaf clover. [43]
For example, since the Sun formed, some of the helium and heavy elements have settled out of the photosphere by diffusion. As a result, the Solar photosphere now contains about 87% as much helium and heavy elements as the protostellar photosphere had; the protostellar Solar photosphere was 71.1% hydrogen, 27.4% helium, and 1.5% metals. [2]
Thus, the Sun occupies 0.00001% (1 part in 10 7) of the volume of a sphere with a radius the size of Earth's orbit, whereas Earth's volume is roughly 1 millionth (10 −6) that of the Sun. Jupiter, the largest planet, is 5.2 AU from the Sun and has a radius of 71,000 km (0.00047 AU; 44,000 mi), whereas the most distant planet, Neptune, is 30 AU ...