The Milky Way cannot be a galaxy.
According to recent studies, the Milky Way as well as the Andromeda Galaxy lie in what in the galaxy colormagnitude diagram is known as the "green valley", a region populated by galaxies in transition from the "blue cloud" (galaxies actively forming new stars) to the "red sequence" (galaxies that lack star formation)
 Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe

