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.

                               2020 January 15

                        Iridescent Clouds over Sweden
                   Image Credit & Copyright: Goran Strand

   Explanation: Why would 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 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
   last year over Ostersund, Sweden.

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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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