Helium is a noble gas element denoted by the atomic symbol H. It has an atomic number of 2, and the average atomic weight of its isotopes is 4.0026. It is a colorless, odorless gas which is present in all natural gas sources.

In many respects, helium is one of the most unusual elements known to science. Helium is far more abundant throughout the rest of the universe than it is here on earth. In fact, helium was first found to exist on the Sun, for which it was named after the Greek word helios. In 1868, French astronomer Pierre Janssen (1824-1907) went to India to study a total solar eclipse. Although lame from a childhood accident, Janssen traveled the world in pursuit of such astronomical events. During the eclipse, he analyzed the wavelengths, or colors, displayed in the Sun's spectrum of light and found a yellow spectral line that he...