Around 2015, astronomers took on the painstaking task of stitching together Hubble Space Telescope images of this galaxy, but that effort had focused on the galaxy's northern half. Still, however, the resulting image showcased a sweeping view of 100 million stars packed into about 1.5 billion pixels.

In the years following the launch of NASA's Hubble Space Telescope, astronomers have tallied over 1 trillion galaxies in the universe. But only one galaxy stands out as the most important nearby stellar island to our Milky Way -- the magnificent Andromeda galaxy (Messier 31).

Hubble Space Telescope mapped Andromeda, revealing a chaotic history shaped by mergers. A 2.5-billion-pixel mosaic shows 200 million stars.