                        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 April 23
    Two airplane contrails, crossing in an X, are shown across the middle
    of the image. They are bright white against a dark blue background. A
    high cloud deck is seen above the crossing, sunlit, contrails. A low
       Sun creates a dark shadow X on the high while clouds. A row of
      buildings runs across the lower part of the image. Please see the
                 explanation for more detailed information.

                              Contrail Shadow X
                    Image Credit & Copyright: Fatih Ekmen

   Explanation: What created this giant X in the clouds? It was the shadow
   of contrails illuminated from below. When airplanes fly, humid engine
   exhaust may form water droplets that might freeze in Earth's cold upper
   atmosphere. These persistent streams of water and ice scatter light
   from the Sun above and so appear bright from below. On rare occasions,
   though, when the Sun is near the horizon, contrails can be lit from
   below. These contrails cast long shadows upwards, shadows that usually
   go unseen unless there is a high cloud deck. But that was just the case
   over Istanbul, Türkiye, earlier this month. Contrails occur all over
   planet Earth and, generally, warm the Earth when the trap infrared
   light but cool the Earth when they efficiently reflect sunlight. The
   image was taken by a surprised photographer in the morning on the way
   to work.

                      Tomorrow's picture: a star's art
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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.

