What information do the spectra provide?
Spectroscopy is the astronomer’s most powerful tool. It is a technique which allows one to determine the brighness of an object as a fuction of wavelength of light, or equivalently color. It turns out that the properties of atoms and molecules leave tell-tale signs in the spectra of virtually all things. By measuring the spectrum of an object one can determine what sorts of elements and molecules exist in the object. In the case of stars the spectrum reveals the contents of only the atmosphere. The interior of the star is shrouded by the atmosphere and cannot be observed directly using spectroscopy.
