Astronomy Picture of the Day

   [1]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 December 28

         IFRAME: [2]https://www.youtube.com/embed/2SnbMTQwDKM?rel=0

                            Sun Halo over Sweden
     Video Credit & Copyright: [3]Håkan Hammar ([4]Vemdalen Ski Resort,
                                 [5]SkiStar)

   Explanation: What's happened to the Sun? Sometimes it looks like the
   Sun is being viewed through a giant [6]lens. In the featured video,
   however, there are actually millions of tiny lenses: [7]ice crystals.
   Water may freeze in the [8]atmosphere into small, flat, six-sided, ice
   crystals. As these [9]crystals flutter to the ground, much time is
   spent with their [10]faces flat and parallel to the ground. An
   [11]observer may find themselves in the same plane as many of the
   falling ice crystals near sunrise or sunset. During this alignment,
   each crystal can act like a miniature lens, refracting sunlight into
   our [12]view and creating [13]phenomena like parhelia, the technical
   term for [14]sundogs. The [15]featured video was taken in late 2017 on
   the side of a ski hill at the [16]Vemdalen Ski Resort in central
   [17]Sweden. Visible in the center is the most direct image of the
   [18]Sun, while two bright [19]sundogs glow prominently from both the
   left and the right. [20]Also visible is the bright [21]22 degree halo
   -- as well as the rarer and much fainter [22]46 degree halo -- also
   created by [23]sunlight refracting through atmospheric ice
   [24]crystals.

                      Tomorrow's picture: giant storms
     __________________________________________________________________

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    Authors & editors: [36]Robert Nemiroff ([37]MTU) & [38]Jerry Bonnell
                                 ([39]UMCP)
          NASA Official: Phillip Newman [40]Specific rights apply.
              [41]NASA Web Privacy Policy and Important Notices
                A service of: [42]ASD at [43]NASA / [44]GSFC
                           & [45]Michigan Tech. U.

References

   1. https://apod.nasa.gov/apod/archivepix.html
   2. https://www.youtube.com/embed/2SnbMTQwDKM?rel=0
   3. https://www.facebook.com/hakanhf
   4. https://www.skistar.com/sv/vara-skidorter/vemdalen/vinter-i-vemdalen/
   5. https://www.skistar.com/en/corporate/
   6. https://en.wikipedia.org/wiki/Lens_(optics)
   7. http://www.its.caltech.edu/~atomic/snowcrystals/halos/halos.htm
   8. https://www.nasa.gov/sites/default/files/images/463940main_atmosphere-layers2_full.jpg
   9. https://en.wikipedia.org/wiki/Ice_crystal
  10. https://www.atoptics.co.uk/halo/orplate.htm
  11. http://littlefun.org/uploads/52410bb8e691b267f97d9278_736.jpg
  12. https://apod.nasa.gov/apod/ap100208.html
  13. http://www.atoptics.co.uk/halo/parhelia.htm
  14. https://apod.nasa.gov/apod/ap990823.html
  15. https://www.facebook.com/hakanhf/videos/10210053095156104/
  16. https://www.skistar.com/en/ski-destinations/vemdalen/winter-in-vemdalen/
  17. http://en.wikipedia.org/wiki/Sweden
  18. https://solarsystem.nasa.gov/solar-system/sun/in-depth/
  19. http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/opt/ice/sd.rxml
  20. http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/halo.html
  21. http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/halo22.html
  22. http://www.atoptics.co.uk/halo/46hal.htm
  23. http://www.atoptics.co.uk/halo/circular.htm
  24. https://apod.nasa.gov/apod/ap200224.html
  25. https://apod.nasa.gov/apod/ap211227.html
  26. https://apod.nasa.gov/apod/archivepix.html
  27. https://apod.nasa.gov/apod/lib/apsubmit2015.html
  28. https://apod.nasa.gov/apod/lib/aptree.html
  29. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  30. https://apod.nasa.gov/apod/calendar/allyears.html
  31. https://apod.nasa.gov/apod.rss
  32. https://apod.nasa.gov/apod/lib/edlinks.html
  33. https://apod.nasa.gov/apod/lib/about_apod.html
  34. http://asterisk.apod.com/discuss_apod.php?date=211228
  35. https://apod.nasa.gov/apod/ap211229.html
  36. http://www.phy.mtu.edu/faculty/Nemiroff.html
  37. http://www.phy.mtu.edu/
  38. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  39. http://www.astro.umd.edu/
  40. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
  41. https://www.nasa.gov/about/highlights/HP_Privacy.html
  42. https://astrophysics.gsfc.nasa.gov/
  43. https://www.nasa.gov/
  44. https://www.nasa.gov/centers/goddard/
  45. http://www.mtu.edu/