I have a BSci in Astronomy and have not yet attended grad school. I work for a world class observatory that uses spectroscopy of some sort in almost all of the science we do. Having only had brief overviews as an undergrad, this book was a perfect next step allowing me to gain a more thorough understanding the science that I am part of. Some prior knowledge of atomic physics is very helpful.
The problems at the end of the chapters are useful to verify understanding of the material.