                        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 December 7

                     Mammatus Clouds over Mount Rushmore
                  Image Credit & Copyright: Laure Mattuzzi

   Explanation: What's that below those strange clouds? Presidents. If you
   look closely, you may recognize the heads of four former US Presidents
   carved into famous Mount Rushmore in South Dakota, USA. More obvious in
   the featured image are the unusual mammatus clouds that passed briefly
   overhead. Both were captured together by a surprised tourist with a
   quick camera in early September. Unlike normal flat-bottomed clouds
   which form when moist and calm air plateaus rise and cool, bumpy
   mammatus clouds form as icy and turbulent air pockets sink and heat up.
   Such turbulent air is frequently accompanied by a thunderstorm. Each
   mammatus lobe spans about one kilometer. The greater mountain is known
   to native Lakota Sioux as Six Grandfathers, deities responsible for the
   directions north, south, east, west, up, and down.

               Tomorrow's picture: an almost great conjunction
     __________________________________________________________________

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

