Virgo Cluster
The spectrum of Messier 90 is blueshifted, which indicates that, net of non-aligned vectors of motion, it gap to galaxy is narrowing. The spectra of most galaxies are redshifted. The blueshift was originally used to argue that Messier 90 was actually an object in the foreground of the Virgo Cluster. However, since the phenomenon was limited mostly to galaxies in the same part of the sky as the Virgo Cluster, it appeared that this inference based on the blueshift was incorrect. Instead, many blueshifts exhibit the large range in velocities of objects within the Virgo Cluster.