This fourth edition of Roy and Clarke's classic textbook has been updated and expanded to include the many developments in modern astronomy and experimental methods. "Astronomy: Principles and Practice" provides a comprehensive and systematic treatment of astronomy, including the essential physical and mathematical groundwork. Divided into four main parts, this volume introduces the concepts and historical development of astronomy, presents a full and detailed course on positional measurements and celestial mechanics, and describes the techniques and instrumentation of astronomical observation and measurement. Suitable for undergraduate students in physics and astronomy, the authors have included many worked examples, problems with answers, a wide selection of practical projects and a directory of relevant and important astronomy web sites. The companion volume "Astronomy: Structure of the Universe" discusses the Solar System, the astrophysics of stars, interstellar matter, galactic structure and cosmology. Combined these two volumes provide a complete course companion.