                        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 July 7
    A landscape shows the sky above, shallow water in front, and hills to
      the right. The sunset sky is filled with beautifully multicolored
   clouds. These clouds are clearly reflected by the calm water in front.
          Please see the explanation for more detailed information.

                        Iridescent Clouds over Sweden
                         Image Credit: Goran Strand

   Explanation: Why are these clouds multi-colored? A relatively rare
   phenomenon in clouds known as iridescence can bring up unusual colors
   vividly -- or even a whole spectrum of colors simultaneously. These
   polar stratospheric clouds also, known as nacreous and mother-of-pearl
   clouds, are formed of small water droplets of nearly uniform size. When
   the Sun is in the right position and, typically, hidden from direct
   view, these thin clouds can be seen significantly diffracting sunlight
   in a nearly coherent manner, with different colors being deflected by
   different amounts. Therefore, different colors will come to the
   observer from slightly different directions. Many clouds start with
   uniform regions that could show iridescence but quickly become too
   thick, too mixed, or too angularly far from the Sun to exhibit striking
   colors. The featured image and an accompanying video were taken late in
   2019 over Ostersund, Sweden.

                 Tomorrow's picture: red planet, blue planet
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       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.

