Helium is a chemical element with the atomic number 2 and represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert monatomic gas that heads up the noble gas series in the periodic table. Its boiling and melting points are the lowest of all the elements. Helium’s low density and low solubility in water make it difficult to extract from natural sources. The majority of helium on Earth was formed during Big Bang nucleosynthesis about 14 billion years ago.
helium was first detected spectroscopically in 1868 by French astronomer Jules Janssen during a total solar eclipse in Guntur India. Scottish chemist Sir William Ramsay discovered it while working with minerals that contained uranium—an element with much higher atomic number than helium—in 1895. Helium was originally believed to be rare on Earth because it is continuously lost to outer space as a result of its high escape velocity: approximately 7 km/s from Earth’s surface. However, large reserves of helium were found underground in 1903 near Dexter Kansas; these deposits are now the largest known source of natural helium.
The name “helium” is derived from Greek ἥλιος (helios), meaning “sun”. In 1871 Ramsay suggested that Janssen’s line might be due to an unknown element in the Sun which he named “helium”, after the Greek god of the sun. On March 26, 1895 Ramsay succeeded in isolating helium on Earth by fractional distillation of liquid air. First he cooled air until it became liquid, then he allowed different fractions (liquids with different boiling points) to boil off separately. The lightest fraction rose first and contained most of what we now call nitrogen; however, it also held small amounts of other gases including argon and methane. When this mixture was heated even further one more gas boiled off before nitrogen: a new gas which Ramsay identified as helium using spectrum analysis.
Ramsay estimated that atmospheric nitrogen consisted of 80% nitrogen and 20% other gases, mostly argon but with some oxygen and carbon dioxide; thus he calculated that about 1/20000th part of atmospheric air was helium. From these data he concluded that if every star were like our Sun (which indeed they are not), then at least one out four hundred would have planets where conditions were right for life similar to ours; many more stars could support life if they had different compositions or conditions. This estimate proved far too optimistic—most stars are very unlike our Sun—but his reasoning was sound: there must be many places in our Milky Way galaxy where conditions are favorable for life as we know it.”