Astronomy Picture of the Day . The Double Nucleus of M31 . ... 11.10.1996 . ... HST Explanation: The center of M31 is twice as unusual as previously thought. In 1991 the Planetary Camera then onboard the Hubble Space Telescope pointed toward the center of our Milky Way 's closest major galactic neighbor: Andromeda (M31). To everyone's surprise, M31's nucleus showed a double structure . ... NASA Web Site Statements, Warnings, and Disclaimers . ... U. Based on Astronomy Picture Of the Day ...