The first edition of this book sold within a relatively short time span of about two years. Nevertheless, this second edition is not just a corrected and updated reprint but has also seen a couple of changes. First of all, SI units are adopted throughout. Equations often used for estimates also are given in the older but still commonly used cgs system. Thus, the reader can choose what suits best. Second, there were a lot of larger and smaller flaws in the first printing which have been corrected. I greatly appreciate the hints and comments given by Andre Balogh, R. A. Cairns, Stanley H. Cowley, Roman Hatzky, Eberhard Moebius, Reinhold Muller-Mellin, Constantinos Paizes, Wilfried Schroder, C. L. Waters, and, last but not least, Gerd Wibberenz. All these people not only helped reduce the numbers of errors but also made valuable sugges tions on better or clearer explanations, topics to cover in more depth, and misleading wording and sentences. I have gratefully taken their suggestions and incorporated them into this edition. For the remaining errors, I take sole responsibility. If you find such a flaw, or have additional suggestions for improvements, please send a brief note to mkallenr@uni-osnabrueck. de. Aside from these minor, though important, modifications there are also some larger changes.
