NED lists 61 aliases from numerous radio, X-ray, QSO, Ultraviolet and even Infrared catalogues. Mrk 501 falls in the class of AGN (Active Galactic Nuclei) which are thought to be ejecting material from a very hot X-ray emitting accretion disc, with one jet shooting out directly along our line of sight. It generally varies from 13.6-13.9V.

400/500mm - 18" (7/30/08): Mrk 501 is one of the brightest and the second closest BL Lacerta objects (blazars) in the sky. At 283x it appeared faint, extremely small, round, ~10" diameter (viewed core only). With averted vision the halo increased to 15"-20". With direct vision a stellar nucleus was visible and the halo nearly disappeared. Located ~6' W of a 6' string of mag 12-13 stars

Notes by Steve Gottlieb