Frank Shu's introductory textbook The Physical Universe is an impressive overview of the field of astronomy. While sufficiently technical for an fairly advanced undergraduate (the physics review chapters are very useful), Shu is careful to keep astronomical concepts in context. He uses the history of astronomy as well as the importance of basic research in his end of chapter "why does this matter?" paragraphs to put these issues into a broader understanding of science. His final chapters about life in the universe start from a biochemical perspective and is one of the best treatments of biology I've read by an astrophysicist. The one disappointing aspect of this textbook is that it has not been updated since it was first published in the 1980's. Many of the cutting edge problems in astrophysics, like the solar neutrino problem, presented here have already been solved, and dark energy/matter was not known at the time of writing. Shu's explanations of astrophysical principles and descriptions are intuitive and reminiscent of Richard Feynman's explanations of physics, and The Physical Universe is a great intro textbook that could be significantly better with an update.