M94
Spiral galaxy M94 was classified Sab because of its extremely bright inner. This bright circular disk is surrounded by a ring of active star-forming regions, traced by blue young star clusters in color images, which sharply separates it from a much less bright outer ring of an older yellowish stellar population. In the outskirts, this region however ends again in a ring with moderate star formation activity, so that M94 is one of the relatively rare galaxies in which two "waves" of stellar formation can be observed. In very long exposures, a further very faint ring, about 15 arc minutes across, becomes visible.