                        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.

                              2019 December 14

                        Interstellar Comet 2I/Borisov
            Image Credit: NASA, ESA, and D. Jewitt (UCLA) et al.

   Explanation: From somewhere else in the Milky Way galaxy, Comet
   2I/Borisov is just visiting the Solar System. Discovered by Crimean
   amateur astronomer Gennady Borisov on August 30, 2019, the first known
   interstellar comet is captured in these two recent Hubble Space
   Telescope images. On the left, a distant background galaxy near the
   line-of-sight to Borisov is blurred as Hubble tracked the speeding
   comet and dust tail about 327 million kilometers from Earth. At right,
   2I/Borisov appears shortly after perihelion, it's closest approach to
   Sun. Borisov's closest approach to our fair planet, a distance of about
   290 million kilometers, will come on December 28. Even though Hubble's
   sharp images don't resolve the comet's nucleus, they do lead to
   estimates of less than 1 kilometer for its diameter.

                       Tomorrow's picture: cloudy day
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
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