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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.

                               2023 December 5
      An illustrations depicts a high energy cosmic ray starting an air
      shower in the Earth's atmosphere. Below is an array of air shower
    detectors. Please see the explanation for more detailed information.

                    Energetic Particle Strikes the Earth
         Illustration Credit: Osaka Metropolitan U./L-INSIGHT, Kyoto
                           U./Ryuunosuke Takeshige

   Explanation: It was one of the most energetic particles ever known to
   strike the Earth -- but where did it come from? Dubbed Amaterasu after
   the Shinto sun goddess, this particle, as do all cosmic rays that
   strike the Earth's atmosphere, caused an air shower of electrons,
   protons, and other elementary particles to spray down onto the Earth
   below. In the featured illustration, a cosmic ray air shower is
   pictured striking the Telescope Array in Utah, USA, which recorded the
   Amaterasu event in 2021 May. Cosmic ray air showers are common enough
   that you likely have been in a particle spray yourself, although you
   likely wouldn't have noticed. The origin of this energetic particle,
   likely the nucleus of an atom, remains a mystery in two ways. First, it
   is not known how any single particle or atomic nucleus can practically
   acquire so much energy, and second, attempts to trace the particle back
   to where it originated did not indicate any likely potential source.

      Open Science: Browse 3,200+ codes in the Astrophysics Source Code
                                   Library
                    Tomorrow's picture: torched by stars
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
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