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 21

                                Unwinding M51
    Image Credit & Copyright: Data - Hubble Heritage Project, Unwinding -
                                 Paul Howell

   Explanation: The arms of a grand design spiral galaxy 60,000
   light-years across are unwound in this digital transformation of the
   magnificent 2005 Hubble Space Telescope portrait of M51. In fact, M51
   is one of the original spiral nebulae, its winding arms described by a
   mathematical curve known as a logarithmic spiral, a spiral whose
   separation grows in a geometric way with increasing distance from the
   center. Applying logarithms to shift the pixel coordinates in the
   Hubble image relative to the center of M51 maps the galaxy's spiral
   arms into diagonal straight lines. The transformed image dramatically
   shows the arms themselves are traced by star formation, lined with
   pinkish starforming regions and young blue star clusters. Companion
   galaxy NGC 5195 (top) seems to alter the track of the arm in front of
   it though, and itself remains relatively unaffected by this unwinding
   of M51. Also known as the spira mirabilis, logarthimic spirals can be
   found in nature on all scales. For example, logarithmic spirals can
   also describe hurricanes, the tracks of subatomic particles in a bubble
   chamber and, of course, cauliflower.

                      Tomorrow's picture: light-weekend
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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