It comes as a surprise to most people when they learn that rarely does a professional astronomer actually look through a telescope. Most of the time, in fact, he isn't interested in the appearance at all. What he actually wants (usually) is a spectroscopic analysis of the light coming from the object being observed.
The biggest telescope cannor resolve a star into anything but a point of light. The information contained in that point of light can tell you a lot about that star. The composition of its atmosphere, its motion, its temperature and more can all be determined by analyzing the light beam.
This book was developed for a third year undergraduate level course. It presumes that the student had a prior course in Quantum Mechanics which covered the Hydrogen Atom, but no further atomic physics or spectroscopy.