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.

                              2019 September 16

                          A Lunar Corona over Turin
        Image Credit & Copyright: Giorgia Hofer (Cortina Astronomical
                                Association)

   Explanation: What are those colorful rings around the Moon? A corona.
   Rings like this will sometimes appear when the Moon is seen through
   thin clouds. The effect is created by the quantum mechanical
   diffraction of light around individual, similarly-sized water droplets
   in an intervening but mostly-transparent cloud. Since light of
   different colors has different wavelengths, each color diffracts
   differently. Lunar Coronae are one of the few quantum mechanical color
   effects that can be easily seen with the unaided eye. The featured
   lunar corona was captured around full Moon above Turin, Italy in 2014.
   Similar coronae that form around the Sun are usually harder to see
   because of the Sun's great brightness.

                  Tomorrow's picture: exoplanet water vapor
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
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