Since its launch on June 1, 1990 the X-ray satellite ROSAT has been orbiting the Earth equipped with the largest and most precise X-ray telescope ever built.

In the ROSAT Survey, the entire sky was mapped and sources were visible a hundred times fainter than in any previous survey. Selected sources were studied in more than 5,000 additional individual observations. Altogether, 120,000 X-ray sources were discovered with ROSAT, twenty-five times more than with all previous X-ray satellites together.

Just as important, more important even than the entire quantitative progress, is the broadening of the scientific horizon mediated by ROSAT. Thus, in the survey with its unlimited field of view, the regions of diffuse X-ray emission, for instance from supernova remnants and cluster of galaxies, were reproduced and spectroscopically analyzed for the first time. With the deepest X-ray exposures in the pointing programme, the puzzle of the cosmic X-ray background could nearly be solved.

Together with the ROSAT team at the Max Planck-Institut für Extraterrestrische Physik, colleagues from twenty astronomical institutes in Germany and about one thousand scientists world-wide are working on the evaluation and interpretation of ROSAT data. In past years the ROSAT calendar with its beautiful ROSAT images had found much attraction. On the occasion of the five-year anniversary of the launch, we have supplemented these pictures by additional images and collected them in an illustrated book. We dedicate it to all friends and sponsors and express our thanks for the excellent co-operation and support.

Joachim Trümper

for the ROSAT team
of the Max-Planck-Institut für Extraterrestrische Physik