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.

                                2021 March 8

                        Three Tails of Comet NEOWISE
                 Image Credit & Copyright: Nicolas Lefaudeux

   Explanation: What created the unusual red tail in Comet NEOWISE?
   Sodium. A spectacular sight back in the summer of 2020, Comet NEOWISE,
   at times, displayed something more than just a surprisingly striated
   white dust tail and a pleasingly patchy blue ion tail. Some color
   sensitive images showed an unusual red tail, and analysis showed much
   of this third tail's color was emitted by sodium. Gas rich in sodium
   atoms might have been liberated from Comet NEOWISE's warming nucleus in
   early July by bright sunlight, electrically charged by ultraviolet
   sunlight, and then pushed out by the solar wind. The featured image was
   captured in mid-July from Brittany, France and shows the real colors.
   Sodium comet tails have been seen before but are rare -- this one
   disappeared by late July. Comet C/2020 F3 (NEOWISE) has since faded,
   lost all of its bright tails, and now approaches the orbit of Jupiter
   as it heads back to the outer Solar System, to return only in about
   7,000 years.

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