Ginga was a Japanese X-ray satellite, launched by ISAS (Institute of Space and Astronautical Science), that measured the time variability of X-rays from active galaxies and quasars in the energy range 1–500 keV. Ginga, which means "galaxy," was known before launch as Astro-C (see Astro- series). It was the third Japanese X-ray astronomy mission, following Hakucho and Tenma. Ginga reentered the Earth's atmosphere on 1 November 1991.