Discovered 1779 by Barnabus Oriani.

M61 was discovered by Barnabus Oriani on May 5, 1779 when following the comet of that year, 6 days before Charles Messier's discovery, who had seen it on the same day as Oriani but mistaken it for the comet. Messier mistook it for two nights more, until he realized that it did not move. As for a small number of others, this object was assigned an own number, H I.139, by William Herschel, who normally avoided to give own numbers to Messier's objects, when he observed and cataloged it on April 17, 1786.

M61 is one of the larger galaxies in the Virgo cluster; its 6 arc minutes of diameter correspond to about 100,000 light years, similar to the diameter of the Milky Way galaxy. Its 10th magnitude corresponds to an absolute magnitude of -21.2.

Four supernovae have been observed in M61: 1926A (12.8 mag) was discovered by Wolf and Reinmuth, 1961I (mag 13, Humason), 1964F (mag 12, Rosino), and 1999gn (13.4 mag, Dimai). NED gives the following types and (alternative values for) maxima: SN 1926A, type IIL, 14pv; SN 1961I, type II, 13.0; SN 1964F, type I, 14.0. The Supernova 1961I appeared in the spiral arms, about 82" from the center, and was photographed by the Lick observatory, see e.g. Burnham (you may also order this image from them as slide or print).