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 1

                         Lunar Halo over Snowy Trees
                    Image Credit & Copyright: Göran Strand

   Explanation: Have you ever seen a halo around the Moon? This fairly
   common sight occurs when high thin clouds containing millions of tiny
   ice crystals cover much of the sky. Each ice crystal acts like a
   miniature lens. Because most of the crystals have a similar elongated
   hexagonal shape, light entering one crystal face and exiting through
   the opposing face refracts 22 degrees, which corresponds to the radius
   of the Moon Halo. A similar Sun Halo may be visible during the day.
   Exactly how ice-crystals form in clouds remains a topic of research. In
   the featured image taken last week from Östersund, Sweden, a complete
   lunar halo was captured over snowy trees and rabbit tracks.

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