WISE gives Milky Way's closest sibling a new look
The Andromeda Galaxy, a spiral galaxy 2.5 million light-years away, is something of a big sister to our own Milky Way. Andromeda contains roughly a trillion stars, a few times more than the Milky Way, but as the nearest major galaxy and the nearest spiral, it is useful for studying the structure of galaxies like our own. (Since astronomers are deeply embedded in the Milky Way, it is difficult to make comprehensive measurements of our home universe.)
NASA launched the Wide-field Infrared Survey Explorer, or WISE, in December to map the sky in infrared wavelengths. The spacecraft has already discovered a new asteroid and comet near Earth, and on Wednesday the space agency released a series of images WISE has captured of known astronomical objects. In this infrared image of Andromeda, bluer light represents stars, which give off a great deal of heat, whereas redder hues mark cooler regions, such as dusty wisps within the galaxy. The blue lobe below the galactic disk is Messier 110, an elliptical galaxy that is one of Andromeda's many satellites.