Helium (He) is a colorless, odorless, tasteless, non-toxic, inert monatomic chemical element that heads the noble gas series in the periodic table and whose atomic number is 2. Its boiling and melting points are the lowest among the elements and it exists only as a gas except in extreme conditions. Extreme conditions are also needed to create the small handful of helium compounds, which are all unstable at standard temperature and pressure. It has a second, rare, stable isotope which is called helium-3. The behavior of liquid helium-4's two fluid phases, helium I and helium II, is important to researchers studying quantum mechanics (in particular the phenomenon of superfluidity) and to those looking at the effects that temperatures near absolute zero have on matter (such as superconductivity).
Helium is the second most abundant and second lightest element in the universe and was one of the elements created in the Big Bang. 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. It is extracted from the natural gas by a low temperature separation process called fractional distillation.
In 1868 the French astronomer Pierre Janssen first detected helium as an unknown yellow spectral line signature in light from a solar eclipse. Since then large reserves of helium have been found in the natural gas fields of the United States, which is by far the largest supplier of the gas. It is used in cryogenics, in deep-sea breathing systems, to cool superconducting magnets, in helium dating, for inflating balloons, for providing lift in airships and as a protective gas for many industrial uses (such as arc welding and growing silicon wafers). A much less serious use is to temporarily change the timbre and quality of one's voice by inhaling a small volume of the gas (see precautions section below).