This false-color radio image of half of Andromeda’s “ring” shows the distribution of hydrogen in the galaxy. The image was created with a special process. Like all disk galaxies, Andromeda rotates; the rotation makes some parts, including associated hydrogen atoms, appear as though they are moving toward us while others seem to be moving away. Astronomers select speed ranges—16 to 26 kilometers per second, for instance—then map out areas that appear to be moving at this rate. Although it is convenient for radio astronomers to process data in this way, it is difficult for others to understand these “velocity maps.” 
    In fact, there is no ring in Andromeda. Because we see