Subj : Daily APOD Report
To   : All
From : Alan Ianson
Date : Mon Aug 30 2021 00:38:40

                        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 August 30

                      A Fire Rainbow over West Virginia
                        Image Credit: Christa Harbig

   Explanation: What's happening to this cloud? Ice crystals in a distant
   cirrus cloud are acting like little floating prisms. Known informally
   as a fire rainbow for its flame-like appearance, a circumhorizon arc
   appears parallel to the horizon. For a circumhorizontal arc to be
   visible, the Sun must be at least 58 degrees high in a sky where cirrus
   clouds present below -- in this case cirrus fibrates. The numerous,
   flat, hexagonal ice-crystals that compose the cirrus cloud must be
   aligned horizontally to properly refract sunlight in a collectively
   similar manner. Therefore, circumhorizontal arcs are somewhat unusual
   to see. The featured fire rainbow was photographed earlier this month
   near North Fork Mountain in West Virginia, USA.

                     Tomorrow's picture: true moon blue
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