Astronomy, astrophysics and space research have developed extensively and rapidly in the last few decades. The new opportunities for observation afforded by space travel, the development of high-sensitivity light detectors and the use of powerful computers have revealed new aspects of the fascinating world of galaxies and quasars, stars and planets. The fourth, completely revised edition of The New Cosmos bears witness to this explosive development. It provides a comprehensive but concise introduction to all of astronomy and astrophysics. It stresses observations and theoretical principles equally, requiring of the reader only basic mathematical and scientific background knowledge. Like its predecessors, this edition of The New Cosmos will be welcomed by students and researchers in the fields of astronomy, physics and earth sciences, as well as by serious amateur astronomers.