Long used in undergraduate and introductory graduate courses, Astrophysical Techniques, Sixth Edition provides a comprehensive account of the instruments, detectors, and techniques employed in astronomy and astrophysics. Emphasizing the underlying unity of all astronomical observations, this popular text provides a coherent state-of-the-art account of the instruments and techniques used in current astronomy and astrophysics. As in earlier editions, the author aims to reduce the trend towards fragmentation of astronomical studies. The underlying unity of all of astronomical observation is emphasized by the layout of the book: the pattern of detection --> imaging --> ancillary techniques has been adopted so that one stage of an observation is encountered together with the similar stages required for all other information carriers. The book is written in a very accessible manner, and most of the mathematics is accessible to those who have attended a mathematics course in their final years at school. Nevertheless, the treatment of the topics in general is at a sufficiently high level to be of use to those professionals seeking technical information in areas of astronomy with which they might not be completely familiar.