Recent advances in observational and theoretical efforts in understanding the nature of cataclysmic variables had reached such maturity that there existed a strong, shared feeling among the workers in this field that an international colloquium sponsored by the International Astronomical Union would be timely. To be more specific, this was due primarily to the accumulation of the new data from satellite observatories, such as the International Ultraviolet Observatory (IUE) and EXOSAT, as well as ground-based optical and radio telescopes, and the advances in modeling the putative accretion disks and the thermo-nuclear run-away phenomena in the vinicity of the white dwarf stars in cataclysmic variables. A series of workshops on this subject held in North America over the past several years and that held in Europe in 1985 had all contributed to the advances in our knowledge that led to IAU Colloguium No. 93, held in Bamberg from the 16th to 19th of June 1986. In all, 157 astronomers from 27 countries participated in this conference. Judging from the papers presented, both invited and contributed, and from the enthusiasm seen in discussions, the meeting was indeed a success.

Space experiments have opened practically all electromagnetic windows on the Universe. A discussion of the most important results obtained with multi-frequency photonic astrophysics experiments will provide new input to advance our knowledge of physics, very often in its more extreme conditions. A multitude of high quality data across the whole electromagnetic spectrum came at the scientific community's disposal a few years after the beginning of the Space Era. With these data we are attempting to explain the physics governing the Universe and its origin, which continues to be a matter of the greatest curiosity for humanity. In this book we describe the latest steps of the investigations born with the advent of space experiments. We highlight the most important results, identify unsolved problems, and comment on perspectives we can reasonably expect. This book aims to provide a useful tool for the reader who is not specialized in space astrophysics and for students. Therefore, the book is written in the form of a review with a still reasonable length, taking into account the complexity of the arguments discussed. We do not claim to present a complete picture of the physics governing the Universe, but have rather selected particular topics for a more thorough discussion. A cross section of essays on historical, modern, and philosophical topics is offered and combined with personal views into tricks of the space astrophysics trade.

The International Scientific Spring Meeting of the Astronomische Ge sellschaft (AG) held at Bamberg in April 1991 was devoted to "Vari abilities in Stars and Galaxies". Time-dependent phenomena are observed in a wide range of as tronomical objects. They are caused by different physical mechanisms (for example by pulsation, by accretion, or by dramatic eruptive events in connection with mass outflow) producing observable intensity vari ations through all wavelengths. Many of the papers in this volume are concerned with galactic stars showing such behaviour (for ex ample cataclysmic variables, symbiotic stars, luminous blue variables (LBVs) and novae). Intrinsic variations of the, magnetic field struc ture on observable time scales are, for instance, a peculiarity of cool, solar-like stars and represent a useful tool to study differential rotation and cycles of activity. Recent results on the investigation of gas motions in the inner regions of the Milky Way system, a study of the bipolar galaxy M 82, observations of variable extragalactic radio sources, the variability of emission lines in active galactic nuclei (AGN) as well as continuum variations of quasars and AGN are discussed by several authors. The yearbook series Reviews in Modern Astronomy of the AG to bring the scientific events of the was established in 1988 in order meetings of the society to the attention of the worldwide astronomical community.

Several decades have elapsed since the publication of any similar book in the German language. The lack of such a book has been felt keenly by all friends of astronomy. In our space age, astronomical knowledge arouses public interest more and more. Practical observation at the telescope depends more than anything else on such knowledge. The educational value of such a training is undisputed. On the other hand, the work of the amateur astronomer can also contribute essentially to the work of the professionals. It is from these points of view that this handbook aims to help with versatile advice. At the same time, the book intends to show the wide range of applied astronomy, as it presents itself to the friend of the stars; in mathematical-physical fields, in precision mechanics and optics, and last but not least in the area of social relations. Beyond the circle of amateur astronomers the book is addressed to lecturers, teachers, students and pupils. It wishes to serve them as a guide to "astronomical experiments", which we suggest should be performed in primary and secondary schools, specialist colleges, and extramural courses.