Prior to the discovery of 3C 273, several other radio sources had been associated with optical counterparts, the first being 3C 48. Also, many active galaxies had been misidentified as variable stars, including the famous BL Lac, W Com, and AU CVn. However, it was not understood what these objects were, since their spectra were unlike those of any known stars. Its spectrum did not resemble that of any normal stars with typical stellar elements. 3C 273 was the first object to be identified as a quasar—an extremely luminous object at an astronomical distance.