- 7 Astronomy is not confined to the exploration of the "courage of omission" and concentrate on those visible sky: Since the fifties, scientists have opened areas that can be conveyed without substantial more and more new windows to the universe, prerequisites; but we have tried to take into making it possible to study numerous new aspects account all crucial aspects and have striven for of cosmic events. factual correctness. We also used this courage The German science satellite ROSAT, circling of omission when personal contributions of the Earth since June I, 1990, is an important milestone investigators working with ROSAT were involved. on this road. Its data have provided us not While we mention scientists by name in the only with a complete survey of the x-ray sky in historical chapters, we preferred to attribute all several colors, but also with important insights ROSAT results to the satellite itself, as it were into normal and exotic cosmic objects. It can be otherwise, the list of names would have grown too said without exaggeration that the entirety of these long, and the danger of forgetting one or the other data has changed our view of the world in which would have been too high. We have tried to find words to describe the we live.