M81 es la galaxia más grande de su grupo, formado por 34 galaxias localizadas en la constelación de la Osa Mayor. Su distancia a la tierra es de unos 11.7 millones de años luz. M81 está ligada gravitatoriamente con M82 y NGC3077.
Messier 81 is the largest galaxy in the M81 Group, a group of 34 galaxies located in the constellation Ursa Major. The distance from the Earth to the group is approximately 11.7 Mly (3.6 Mpc), making this one of the closest groups to the Local Group, which contains the Milky Way. M81 is gravitationally interacting with Messier 82 and NGC 3077. The interactions have stripped some hydrogen gas away from all three galaxies, leading to the formation of filamentary gas structures in the group. Moreover, the interactions have also caused some interstellar gas to fall into the centers of Messier 82 and NGC 3077, which has led to strong starburst activity (or the formation of many stars) within the centers of these two galaxies.