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.

                                2021 April 22

                          Planet Earth at Twilight
    Image Credit: ISS Expedition 2 Crew, Gateway to Astronaut Photography
                               of Earth, NASA

   Explanation: No sudden, sharp boundary marks the passage of day into
   night in this gorgeous view of ocean and clouds over our fair planet
   Earth. Instead, the shadow line or terminator is diffuse and shows the
   gradual transition to darkness we experience as twilight. With the Sun
   illuminating the scene from the right, the cloud tops reflect gently
   reddened sunlight filtered through the dusty troposphere, the lowest
   layer of the planet's nurturing atmosphere. A clear high altitude
   layer, visible along the dayside's upper edge, scatters blue sunlight
   and fades into the blackness of space. This picture was taken in June
   of 2001 from the International Space Station orbiting at an altitude of
   211 nautical miles. But you can check out the vital signs of Planet
   Earth Now.

                            Celebrate: Earth Day
                  Tomorrow's picture: Planet Earth at Night
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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                      A service of: ASD at NASA / GSFC
                             & Michigan Tech. U.
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