The Orbiting Astronomical Observatory 2 (OAO-2, nicknamed Stargazer) was the first successful space telescope (the first space telescope being OAO-1, which failed to operate once in orbit), launched on December 7, 1968. An Atlas-Centaur rocket launched it into a nearly circular 750-kilometre (470 mi) altitude Earth orbit. Data was collected in ultraviolet from many sources including comets, planets, and galaxies. It had two major instrument sets facing in opposite directions; the Smithsonian Astrophysical Observatory (SAO) and the Wisconsin Experiment Package (WEP). One discovery was large halos of hydrogen gas around comets, and it also observed Nova Serpentis, which was a nova discovered in 1970.