Astronomy Picture of the Day

    Discover the cosmos! Each day a different image or photograph of our
      fascinating universe is featured, along with a brief explanation
                    written by a professional astronomer.

                               2020 August 27

                          Shell Galaxies in Pisces
                    Image Credit & Copyright: Martin Pugh

   Explanation: This intergalactic skyscape features a peculiar system of
   galaxies cataloged as Arp 227 some 100 million light-years distant.
   Swimming within the boundaries of the constellation Pisces, Arp 227
   consists of the two galaxies prominent right of center, the curious
   shell galaxy NGC 474 and its blue, spiral-armed neighbor NGC 470. The
   faint, wide arcs or shells of NGC 474 could have been formed by a
   gravitational encounter with neighbor NGC 470. Alternately the shells
   could be caused by a merger with a smaller galaxy producing an effect
   analogous to ripples across the surface of a pond. The large galaxy on
   the top lefthand side of the deep image, NGC 467, appears to be
   surrounded by faint shells too, evidence of another interacting galaxy
   system. Intriguing background galaxies are scattered around the field
   that also includes spiky foreground stars. Of course, those stars lie
   well within our own Milky Way Galaxy. The field of view spans 25 arc
   minutes or about 1/2 degree on the sky.

                      Tomorrow's picture: in the valley
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