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.

                               2026 January 9
    [2]See Explanation. Clicking on the picture will download the highest
                        resolution version available.

                     Ice Halos by Moonlight and Sunlight
                Image Credit & [3]Copyright: Antonella Cicala

   Explanation: Both Moon and Sun create beautiful [4]ice halos in planet
   Earth's sky. In fact, the two brightest celestial beacons are each
   surrounded by a [5]complex of ice halos in these photos of the sky
   above Chamonix-Mont-Blanc in France. The panels were recorded one night
   (left) and the following day at the end of December 2025. Similar
   [6]ice halos appear in moonlight and sunlight because they are all
   formed through the geometry of flat, hexagonal ice crystals. The ice
   crystals reflect and refract light as they flutter in the cold
   atmosphere above the mountain resort. In the pictures both Moon and Sun
   are surrounded by a more commonly seen 22 degree circular halo. Bright
   and sometimes colorful patches at the intersections of the 22 degree
   circular halos with the indicated [7]parselenic and parhelic arcs are
   also known as [8]Moon dogs and [9]Sun dogs.

                    Tomorrow's picture: opposite the Sun
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    Authors & editors: [21]Robert Nemiroff ([22]MTU) & [23]Jerry Bonnell
                                 ([24]UMCP)
          NASA Official: Amber Straughn [25]Specific rights apply.
            [26]NASA Web Privacy, [27]Accessibility, [28]Notices;
                A service of: [29]ASD at [30]NASA / [31]GSFC,
                         [32]NASA Science Activation
                           & [33]Michigan Tech. U.

References

   1. https://apod.nasa.gov/apod/archivepix.html
   2. https://apod.nasa.gov/apod/image/2601/TransitionsLight.jpeg
   3. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
   4. https://en.wikipedia.org/wiki/Halo_(optical_phenomenon)
   5. https://apod.nasa.gov/apod/ap241225.html
   6. https://ui.adsabs.harvard.edu/abs/2022JQSRT.29008313M/abstract
   7. https://cloudatlas.wmo.int/en/parhelic-circle.html
   8. https://apod.nasa.gov/apod/ap160321.html
   9. https://apod.nasa.gov/apod/ap250215.html
  10. https://apod.nasa.gov/apod/ap260108.html
  11. https://apod.nasa.gov/apod/archivepix.html
  12. https://apod.nasa.gov/apod/lib/apsubmit2015.html
  13. https://apod.nasa.gov/apod/lib/aptree.html
  14. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  15. https://apod.nasa.gov/apod/calendar/allyears.html
  16. https://apod.com/feed.rss
  17. https://apod.nasa.gov/apod/lib/edlinks.html
  18. https://apod.nasa.gov/apod/lib/about_apod.html
  19. https://asterisk.apod.com/discuss_apod.php?date=260109
  20. https://apod.nasa.gov/apod/ap260110.html
  21. http://www.phy.mtu.edu/faculty/Nemiroff.html
  22. http://www.phy.mtu.edu/
  23. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  24. http://www.astro.umd.edu/
  25. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
  26. https://www.nasa.gov/about/highlights/HP_Privacy.html
  27. https://www.nasa.gov/general/accessibility/
  28. https://www.nasa.gov/privacy/
  29. https://astrophysics.gsfc.nasa.gov/
  30. https://www.nasa.gov/
  31. https://www.nasa.gov/centers/goddard/
  32. https://science.nasa.gov/learners
  33. http://www.mtu.edu/