Introductory Remarks

The philosopher Auguste Comte (1798–1857) asserted that man would never know the chemical composition of the stars. It is therefore ironical that Gustav Kirchhoff (1824–1887) discovered the laws of spectroscopy at about the same time as Comte's death. With the help of the principles articulated by Kirchhoff we now claim knowledge of the composition not only of the nearby stars, but of galaxies so distant that it has taken a substantial fraction of the age of the universe for their light to reach us.

In this chapter we will review the laws of atomic and molecular spectroscopy that enable us to analyze the electromagnetic radiation from space. Naturally, we cannot give a complete account of these rather complicated topics. There is only space to highlight the nomenclature, and in some cases provide heuristic insight into the more important formulae.

The following chapters will deal with the application of atomic and molecular physics to chemical analyses of stars and stellar systems, and interstellar material.

Atomic Spectra: The Nomenclature of LS Coupling

The identification of spectral lines in a star is done with the help of certain reference volumes, the most important of which is possibly C. E. Moore's (1972) A Multiplet Table of Astrophysical Interest. While the basic work appeared as a series of the publications of the Princeton Observatory, the demand for this material was so great that it has gone through one major revision and innumerable reprints and updates.