ROSAT

ROSAT was a German-led X-ray astronomy satellite that surveyed the sky and observed cosmic X-ray sources from 1990 to 1999.

Wolter telescope: A grazing-incidence telescope that uses nested curved mirrors to focus X-rays. ROSAT’s X-ray Telescope used this mirror design to focus incoming radiation.
German Aerospace Center: Germany’s national aeronautics and space research organization, known by the acronym DLR. DLR led the mission and supplied the spacecraft and X-ray telescope.
X-ray source catalog: A compiled list of astronomical objects detected through their X-ray emission. ROSAT’s catalogs gave astronomers positions and measurements for sources across the sky.
ROSAT Bright Source Catalog: A catalog of bright X-ray sources detected in the ROSAT All-Sky Survey. It provided a widely used, well-characterized subset of the survey detections.
Uhuru: The first satellite dedicated to X-ray astronomy, which conducted an all-sky survey in the early 1970s. Uhuru pioneered X-ray source surveys, while ROSAT later achieved much greater sensitivity in soft X-rays.
Soft X-ray: An X-ray with relatively low photon energy, typically below a few kiloelectronvolts. ROSAT was especially sensitive to this energy range, which interstellar gas readily absorbs.
NASA: The United States government agency responsible for civilian space exploration and aeronautics research. NASA provided launch services and instruments for ROSAT’s international mission.
Active galactic nucleus: A compact, luminous galactic center powered by matter accreting onto a supermassive black hole. ROSAT detected many active galactic nuclei, including objects obscured at other wavelengths.
ROSAT Faint Source Catalog: A catalog of faint X-ray sources detected in the ROSAT All-Sky Survey. It extended the survey’s reach to much weaker sources than the bright-source catalog.
EXOSAT: The European Space Agency’s X-ray observatory, operational from 1983 to 1986. EXOSAT emphasized timing and pointed studies rather than ROSAT’s defining soft-X-ray sky survey.

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