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 August 30
    [2]The picture shows a solar circumhorizontal arc -- nicknamed a fire
   rainbow -- over West Virgina, USA. Please see the explanation for more
                            detailed information.

                      A Fire Rainbow over West Virginia
                       Image Credit: [3]Christa Harbig

   Explanation: What's happening to this cloud? Ice crystals in a distant
   cirrus cloud are acting like little floating [4]prisms. Known
   informally as a fire rainbow for its flame-like appearance, a
   [5]circumhorizon arc appears parallel to the horizon. For a
   [6]circumhorizontal arc to be visible, [7]the Sun must be at least 58
   degrees high in a sky where [8]cirrus clouds present below -- in this
   case [9]cirrus fibrates. The numerous, flat, [10]hexagonal ice-crystals
   that compose the [11]cirrus cloud must be [12]aligned horizontally to
   properly [13]refract sunlight in a collectively similar manner.
   Therefore, [14]circumhorizontal [15]arcs are [16]somewhat unusual to
   see. The [17]featured fire rainbow was photographed earlier this month
   near [18]North Fork Mountain in [19]West Virginia, [20]USA.

                     Tomorrow's picture: true moon blue
     __________________________________________________________________

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    Authors & editors: [32]Robert Nemiroff ([33]MTU) & [34]Jerry Bonnell
                                 ([35]UMCP)
          NASA Official: Phillip Newman [36]Specific rights apply.
              [37]NASA Web Privacy Policy and Important Notices
                A service of: [38]ASD at [39]NASA / [40]GSFC
                           & [41]Michigan Tech. U.

References

   1. https://apod.nasa.gov/apod/archivepix.html
   2. https://apod.nasa.gov/apod/image/2108/FireRainbow_Harbig_4000.jpg
   3. https://www.facebook.com/christa.harbig.photos/
   4. http://micro.magnet.fsu.edu/primer/java/scienceopticsu/newton/
   5. https://en.wikipedia.org/wiki/Circumhorizon_arc
   6. https://www.atoptics.co.uk/halo/cha2.htm
   7. https://solarsystem.nasa.gov/solar-system/sun/overview/
   8. https://en.wikipedia.org/wiki/Cirrus_cloud
   9. https://www.colweather.org.uk/gal-clouds-cirrus.php#Cirrus fibratus
  10. http://www.atoptics.co.uk/halo/orplate.htm
  11. https://en.wikipedia.org/wiki/Cirrus_cloud
  12. https://www.atoptics.co.uk/halo/platcol.htm
  13. http://youtube.com/watch?v=U98KPM2b9IA
  14. https://apod.nasa.gov/apod/ap190519.html
  15. https://apod.nasa.gov/apod/ap151215.html
  16. https://i.pinimg.com/550x/81/21/c0/8121c0291fa14d1fe52b9eb007741cac.jpg
  17. https://www.facebook.com/photo?fbid=4794142133932422
  18. https://youtu.be/kROh8JwKnOk
  19. https://en.wikipedia.org/wiki/West_Virginia
  20. https://en.wikipedia.org/wiki/United_States
  21. https://apod.nasa.gov/apod/ap210829.html
  22. https://apod.nasa.gov/apod/archivepix.html
  23. https://apod.nasa.gov/apod/lib/apsubmit2015.html
  24. https://apod.nasa.gov/apod/lib/aptree.html
  25. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  26. https://apod.nasa.gov/apod/calendar/allyears.html
  27. https://apod.nasa.gov/apod.rss
  28. https://apod.nasa.gov/apod/lib/edlinks.html
  29. https://apod.nasa.gov/apod/lib/about_apod.html
  30. http://asterisk.apod.com/discuss_apod.php?date=210830
  31. https://apod.nasa.gov/apod/ap210831.html
  32. http://www.phy.mtu.edu/faculty/Nemiroff.html
  33. http://www.phy.mtu.edu/
  34. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  35. http://www.astro.umd.edu/
  36. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
  37. https://www.nasa.gov/about/highlights/HP_Privacy.html
  38. https://astrophysics.gsfc.nasa.gov/
  39. https://www.nasa.gov/
  40. https://www.nasa.gov/centers/goddard/
  41. http://www.mtu.edu/