Messier 101 (M101, NGC 5457) was discovered by Pierre Méchain on March 27, 1781, and added as one of the last entries in Charles Messier's catalog. It was one of the first "spiral nebula" identified as such, in 1851 by William Parsons, the third Earl of Rosse.
The distance of M101 has been determined by the measurement of Cepheid variables with the Hubble Space Telescope in 1994/95 to be about 24 +/- 2 million light years
