The Composition of stars is a very important and interesting field for astronomers. Stars begin their life when an ordinary dense cloud of interstellar matter becomes unstable and begins to collapse. The composition of such a cloud of matter determines the composition of the star which results from the collapse. Astronomers study the spectrum of the Sun to determine it's chemical composition, since it is the biggest star we are familiar with. In the visible region alone, from 4000 to 7000 angstroms (10-10 Meters), there are thousands of absorption lines in the solar spectrum. These lines have been cataloged, and tell us that there are 67 chemical elements identified in the Sun. There are probably even more elements in the Sun that are present in such a small amount that our most modern instruments can't detect them.
10 Most common elements in the Sun
Hydrogen is the most abundant element in the Sun, followed by helium. Those two together make up 99.9 percent by number of the total atoms in the Sun! This is also what we find in the composition of the Universe as a whole. When other stars are studied it is found that most stars are composed of around 70 percent hydrogen and 28 percent helium by mass, very similar to what we see in the Sun. The Sun burns hydrogen into helium at it's center, or "core". This is the chain of nuclear fusion that powers the Sun. The net effect is that four hydrogen nuclei combine to create one helium nucleus, some gamma radiation and two neutrinos. The gamma-ray photons slowly lose energy as they pass through the solar interior, and the energy eventually escapes in the form of visible light!