Spectroscopy

Abstract

Spectroscopy is a major tool for learning the nature of celestial sources. It tells us about composition, temperatures, motions, and the general physical circumstances of those sources. The most common instrument for spectroscopy is a diffraction-grating spectrograph, which spreads the light into its panoply of colors. For many years spectrographs were designed to use photographic plates, but now CCD detectors are used because they are more sensitive and give photometrically better results more directly, without the need for wet processing or densitometers. The optical design of the spectrographs nevertheless remains much the same, but with gains accruing from improvements in the quality of the optics. There are, however, several designs that have been quite overlooked.