                        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.

                              2022 November 20
    The featured image shows a dark field with a photographer lit in red
   imaging a night sky tinged with green airglow and decorated with clouds
        that appear collectively like a giant spiral. Please see the
                 explanation for more detailed information.

                         Airglow Ripples over Tibet
                     Image Credit & Copyright: Jeff Dai

   Explanation: Why would the sky look like a giant target? Airglow.
   Following a giant thunderstorm over Bangladesh in late April, giant
   circular ripples of glowing air appeared over Tibet, China, as pictured
   here. The unusual pattern is created by atmospheric gravity waves,
   waves of alternating air pressure that can grow with height as the air
   thins, in this case about 90-kilometers up. Unlike auroras powered by
   collisions with energetic charged particles and seen at high latitudes,
   airglow is due to chemiluminescence, the production of light in a
   chemical reaction. More typically seen near the horizon, airglow keeps
   the night sky from ever being completely dark.

                      Tomorrow's picture: butterfly sky
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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                             & Michigan Tech. U.

