Spectra of Comets and Their Interpretation

Important progress has been made in the study of cometary spectra in recent years thanks to the introduction of high resolution. Spectra of comets have been taken with the coudé spectrographs of large telescopes. Thus the precision of the wavelength measurements has been increased appreciably, new emission lines have been discovered, some of which have been identified, and the analysis of the detailed structure of molecular bands has become possible. Similarly, some information has been derived concerning the kinematical and the spatial structure of comets' heads. On the theoretical side, efforts have been made to take advantage of the higher quality of the new observational data, and a better interpretation of these data has been obtained in some cases. It is not the purpose of the present review to give a complete description of the observational material now available, especially since such a description can be found in a recent .article by Swings (1). Rather shall we emphasize the theoretical aspects of the study of the spectra of comets and present a critical discussion of recent investigations regarding the details of the production of the cometary light