                        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.

                                2022 July 12

                        Noctilucent Clouds over Paris
                     Credit & Copyright: Bertrand Kulik

   Explanation: It's northern noctilucent cloud season. Composed of small
   ice crystals forming only during specific conditions in the upper
   atmosphere, noctilucent clouds may become visible at sunset during late
   summer when illuminated by sunlight from below. Noctilucent clouds are
   the highest clouds known and now established to be polar mesospheric
   clouds observed from the ground. Although observed with NASA's AIM
   satellite since 2007, much about noctilucent clouds remains unknown and
   so a topic of active research. The featured image shows expansive and
   rippled noctilucent clouds wafting over Paris, France. This year,
   several northern locations are already reporting especially vivid
   displays of noctilucent clouds.

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