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 May 30

                  Green Flashes: Sun, Moon, Venus, Mercury
               Image Credit & Copyright: Marcella Giulia Pace

   Explanation: Follow a sunset on a clear day against a distant horizon
   and you might glimpse green just as the Sun disappears from view. The
   green flash is caused by refraction of light rays traveling to the eye
   over a long path through the atmosphere. Shorter wavelengths refract
   more strongly than longer redder wavelengths and the separation of
   colors lends a green hue to the last visible vestige of the solar disk.
   It's harder to see a green flash from the Moon, not to mention the
   diminutive disks of Venus and Mercury. But a telescope or telephoto
   lens and camera can help catch this tantalizing result of atmospheric
   refraction when the celestial bodies are near the horizon. From Sicily,
   the top panels were recorded on March 18, 2019 for the Sun and May 8,
   2020 for the Moon. Also from the Mediterranean island, the bottom
   panels were shot during the twilight apparition of Venus and Mercury
   near the western horizon on May 24.

                      Tomorrow's picture: green arches
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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.

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