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                           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.   
      
                                   2024 April 6   
      
                                   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.   
      
                NASA Coverage: Total Solar Eclipse of 2024 April 8   
                          Tomorrow's picture: clear skies   
        __________________________________________________________________   
      
          Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)   
               NASA Official: Amber Straughn Specific rights apply.   
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                         A service of: ASD at NASA / GSFC,   
                              NASA Science Activation   
                                & Michigan Tech. U.   
      
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