﻿ 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. 2023 December 20 [2]A building is seen from a distance on white snow and with mountains in the background. An ice-crystal filled sky is seen above. Superposed on the night sky are numerous curving whisps -- halos of ice reflecting background moonlight. Please see the explanation for more detailed information. Ice Halos over Bavaria Image Credit & Copyright: [3]Bastian Werner Explanation: What's causing those unusual sky arcs? Ice crystals. While crossing a field of fresh snow near [4]Füssen, [5]Bavaria, [6]Germany, earlier this month, the photographer noticed that he had entered an ice fog. For suspended water to freeze into an [7]ice fog requires quite cold temperatures, and indeed the air temperature on this day was measured at well below zero. The [8]ice fog reflected light from the [9]Sun setting behind [10]St. Coleman Church. The result was one of the [11]greatest spectacles the photographer has ever seen. First, the spots in the [12]featured picture are not background stars but suspended ice and snow. Next, two prominent [13]ice halos are visible: the [14]22-degree halo and the [15]46-degree [16]halo. Multiple [17]arcs are also [18]visible, including, from top to bottom, [19]antisolar (subsun), [20]circumzenithal, [21]Parry, [22]tangent, and [23]parhelic (horizontal). Finally, the [24]balloon shaped curve connecting the top arc to the Sun is the [25]rarest of all: it is the [26]heliac arc, created by reflection from the sides of [27]hexagonally shaped [28]ice crystals suspended in a horizontal orientation. Tomorrow's picture: open space __________________________________________________________________ [29]< | [30]Archive | [31]Submissions | [32]Index | [33]Search | [34]Calendar | [35]RSS | [36]Education | [37]About APOD | [38]Discuss | [39]> __________________________________________________________________ Authors & editors: [40]Robert Nemiroff ([41]MTU) & [42]Jerry Bonnell ([43]UMCP) NASA Official: Phillip Newman [44]Specific rights apply. [45]NASA Web Privacy Policy and Important Notices A service of: [46]ASD at [47]NASA / [48]GSFC, [49]NASA Science Activation & [50]Michigan Tech. U. References 1. https://apod.nasa.gov/apod/archivepix.html 2. https://apod.nasa.gov/apod/image/2312/BavarianHalos_Werner_1500.jpg 3. https://www.instagram.com/bastianw.de/ 4. https://youtu.be/5GjgTrY_cjA 5. https://en.wikipedia.org/wiki/Bavaria 6. https://en.wikipedia.org/wiki/Germany 7. https://en.wikipedia.org/wiki/Ice_fog 8. https://apod.nasa.gov/apod/ap211228.html 9. https://science.nasa.gov/sun/ 10. https://www.reddit.com/r/churches/comments/18h9p41/st_colemans_church_in_schwangau_ostallgäu_bavaria/ 11. https://img.buzzfeed.com/buzzfeed-static/static/campaign_images/web05/2011/11/28/10/this-cat-is-totally-amazed-28550-1322493178-12.jpg?resize=600:* 12. https://www.instagram.com/p/C0mLwRBN2Xf/ 13. https://old.atoptics.co.uk/halosim.htm 14. https://apod.nasa.gov/apod/ap210201.html 15. https://en.wikipedia.org/wiki/46°_halo 16. https://en.wikipedia.org/wiki/Halo_(optical_phenomenon) 17. https://old.atoptics.co.uk/halo/spsun.htm 18. https://old.atoptics.co.uk/halo/common.htm 19. https://atoptics.wordpress.com/2014/05/09/the-mystery-of-bright-antisolar-arcs/ 20. https://en.wikipedia.org/wiki/Circumzenithal_arc 21. https://en.wikipedia.org/wiki/Parry_arc 22. https://en.wikipedia.org/wiki/Tangent_arc 23. https://en.wikipedia.org/wiki/Parhelic_circle 24. https://apod.nasa.gov/apod/ap030606.html 25. https://old.atoptics.co.uk/halo/whyinfr.htm 26. https://www.storyofsnow.com/blog1.php/a-rare-heliac-arc-plus-1 27. https://en.wikipedia.org/wiki/Ice_crystal#/media/File:Hexagonal_Ice_Crystals.svg 28. https://old.atoptics.co.uk/halo/platcol.htm 29. https://apod.nasa.gov/apod/ap231219.html 30. https://apod.nasa.gov/apod/archivepix.html 31. https://apod.nasa.gov/apod/lib/apsubmit2015.html 32. https://apod.nasa.gov/apod/lib/aptree.html 33. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search 34. https://apod.nasa.gov/apod/calendar/allyears.html 35. https://apod.com/feed.rss 36. https://apod.nasa.gov/apod/lib/edlinks.html 37. https://apod.nasa.gov/apod/lib/about_apod.html 38. https://asterisk.apod.com/discuss_apod.php?date=231220 39. https://apod.nasa.gov/apod/ap231221.html 40. http://www.phy.mtu.edu/faculty/Nemiroff.html 41. http://www.phy.mtu.edu/ 42. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html 43. http://www.astro.umd.edu/ 44. https://apod.nasa.gov/apod/lib/about_apod.html#srapply 45. https://www.nasa.gov/about/highlights/HP_Privacy.html 46. https://astrophysics.gsfc.nasa.gov/ 47. https://www.nasa.gov/ 48. https://www.nasa.gov/centers/goddard/ 49. https://science.nasa.gov/learners 50. http://www.mtu.edu/