User:Ashill/Solar abundances

Chemical composition
The Sun is composed of chemical elements. The dominant elements are hydrogen and helium; they account for roughly 3/4 and 1/4 of the mass of the Sun, respectively. All heavier elements, called "metals" in astronomy, account for less than 2 percent of the mass. The most abundant metals are oxygen (roughly 1% of the Sun's mass), carbon (0.3%), neon (0.2%), and iron (0.2%). Initially, the Sun inherited its chemical composition from the interstellar medium out of which it formed: the hydrogen and helium in the Sun were produced by Big Bang nucleosynthesis, while the metals were produced by stellar nucleosynthesis in previous generations of stars. In the inner portions of the Sun, nuclear fusion has modified the composition by converting hydrogen into helium, so the innermost portion of the Sun is now roughly 60% helium, with the metal abundance unchanged. Because the interior of the Sun is radiative, not convective (see Structure above), the photosphere retains essentially the initial composition. The chemical composition of the photosphere is normally considered representative of the composition of the primordial Solar System.

Element diffusion
The Sun is composed of chemical elements. Of particular scientific interest is the diffusion of these elements inside the Sun, i.e. their distribution inside the star's interior. The diffusion of solar elements is determined by many variables, including gravity, which causes the heavier elements (e.g. helium in absence of other heavier elements) to stick to the centre of the solar mass while the non-heavy elements (e.g. hydrogen) diffuse towards the exterior of the Sun.