determination accuracy was 6 arcsec. The ROSAT mission was divided into two phases: After a two-month on-orbit calibration and verification period, an all-sky survey was performed for six months using the PSPC in the focus of XRT, and in two XUV bands using the WFC. The survey was carried out in the scan mode. The second phase consists of the remainder of the mission and was devoted to pointed observations of selected astrophysical sources. In ROSAT's pointed phase, observing time was allocated to Guest Investigators from all three participating countries through peer review of submitted proposals. ROSAT had a design life of 18 months, but was expected to operate beyond its nominal lifetime. Instruments X-ray Telescope (XRT) The main assembly was a German-built imaging X-ray Telescope (XRT) with three focal plane instruments: two German Position Sensitive Proportional Counters (PSPC) and the US-supplied High Resolution Imager (HRI). The X-ray mirror assembly was a grazing incidence four-fold nested Wolter I telescope with an diameter aperture and focal length. The angular resolution was less than 5 arcsec at half energy width. The XRT assembly was sensitive to X-rays between 0.1 and 2 keV. Position Sensitive Proportional Counters (two) (PSPC) Each Position Sensitive Proportional Counter (PSPC) is a thin-window gas counter. Each incoming X-ray photon produces an electron cloud whose position and charge are detected using two wire grids. The photon position is determined with an accuracy of about 120 micrometers. The electron cloud's charge corresponds to the photon energy, with a nominal spectral bandpass 0.1-2.4 keV. High Resolution Imager (HRI) The US-supplied High Resolution Imager used a crossed grid detector with a position accuracy to 25 micrometers. The instrument was damaged by solar exposure on 20 September 1998. Wide Field Camera (WFC) The Wide Field Camera (WFC) was a UK-supplied extreme ultraviolet (XUV) telescope co-aligned with the XRT and covered the wave band between 300 and 60 angstroms (0.042 to 0.21 keV). Highlights X-ray all-sky survey catalog, more than 150,000 objects XUV all-sky survey catalog (479 objects) Source catalogs from the pointed phase (PSPC and HRI) containing ~ 100,000 serendipitous sources Detailed morphology of supernova remnants and clusters of galaxies. Detection of shadowing of diffuse X-ray emission by molecular clouds. Detection of pulsations from Geminga. Detection of isolated neutron stars. Discovery of X-ray emission from comets. Observation of X-ray emission from the collision of Comet Shoemaker-Levy with Jupiter. Catalogues 1RXS – an acronym