                        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 February 10

                        Firing Lasers to Tame the Sky
     Image Credit & Copyright: Juan Carlos Muņoz / ESO; Text: Juan Carlos
                                    Muņoz

   Explanation: Why do stars twinkle? Our atmosphere is to blame as
   pockets of slightly off-temperature air, in constant motion, distort
   the light paths from distant astronomical objects. Atmospheric
   turbulence is a problem for astronomers because it blurs the images of
   the sources they want to study. The telescope featured in this image,
   located at ESO's Paranal Observatory, is equipped with four lasers to
   combat this turbulence. The lasers are tuned to a color that excites
   atoms floating high in Earth's atmosphere -- sodium left by passing
   meteors. These glowing sodium spots act as artificial stars whose
   twinkling is immediately recorded and passed to a flexible mirror that
   deforms hundreds of times per second, counteracting atmospheric
   turbulence and resulting in crisper images. The de-twinkling of stars
   is a developing field of technology and allows, in some cases,
   Hubble-class images to be taken from the ground. This technique has
   also led to spin-off applications in human vision science, where it is
   used to obtain very sharp images of the retina.

                       Tomorrow's picture: open space
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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.

