How much iron is in the Sun?

This article traces the historical and scientific development of understanding the elemental composition of the Sun, with a particular focus on the solar iron abundance. It outlines key eras in research, from early spectroscopic observations and ionization theory breakthroughs to the adoption of curve of growth methods, intense academic debates in the late 20th century, and the modern digital era employing three-dimensional, non-local thermodynamic equilibrium (NLTE) models. The solar iron abundance, expressed on the astronomical logarithmic scale where hydrogen is set at 12 dex, has been refined over time to a current consensus near 7.5 dex, consistent with measurements from CI chondrite meteorites. This progression exemplifies how advances in theory, technology, and collaborative scrutiny have shaped our understanding of the Sun’s composition, which is crucial for insights into stellar evolution and the formation of the solar system.