An Etymological Dictionary of Astronomy and Astrophysics

The abundance of a → chemical element as determined from the observation of solar → spectral lines. The solar chemical composition is an important ingredient in our understanding of the formation, structure and evolution of both the Sun and our solar system. Furthermore, it is an essential reference standard against which the elemental contents of other astronomical objects are compared (Asplund et al. 2009, arXiv:0909.0948). The photospheric abundances relative to hydrogen are not representative of the → protosun, or global → solar system abundances.
This is because heavy-element fractionation in the Sun has altered photospheric abundances (Lodders 2003, ApJ 591, 1220).

See also: → solar; → photospheric; → abundance.