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.

                               2024 January 3
   [2]A flat landscape with a pond is imaged at night below a starfield. A
    multicolored aurora is seen in an arc across the image center. Around
   this arc is another red arc that is particularly smooth. Please see the
                 explanation for more detailed information.

                         A SAR Arc from New Zealand
   Image Credit & Copyright: [3]Tristian McDonald; Text: [4]Tiffany Lewis
                            ([5]Michigan Tech U.)

   Explanation: What is that unusual red halo surrounding this aurora? It
   is a Stable Auroral Red (SAR) arc. [6]SAR arcs are rare and have only
   been acknowledged and studied since 1954. The [7]featured wide-angle
   photograph, capturing nearly an entire [8]SAR arc surrounding more
   common green and red aurora, was taken earlier this month from
   [9]Poolburn, [10]New Zealand, during an especially energetic
   [11]geomagnetic storm. Why [12]SAR arcs form remains a topic of
   [13]research, but is likely related to [14]Earth's protective magnetic
   field, a field created by [15]molten iron flowing deep inside the
   [16]Earth. This magnetic field usually redirects incoming charged
   particles from the [17]Sun's wind toward the Earth's poles. However, it
   also traps a [18]ring of ions closer to the equator, where they can
   gain energy from the [19]magnetosphere during high [20]solar activity.
   The energetic electrons in this [21]ion ring can collide with and
   excite oxygen higher in [22]Earth's ionosphere than typical
   [23]auroras, causing the oxygen to glow red. [24]Ongoing research has
   uncovered evidence that a red SAR arc [25]can even transform into a
   [26]purple and green [27]STEVE.

                       Tomorrow's picture: open space
     __________________________________________________________________

      [28]< | [29]Archive | [30]Submissions | [31]Index | [32]Search |
   [33]Calendar | [34]RSS | [35]Education | [36]About APOD | [37]Discuss |
                                    [38]>
     __________________________________________________________________

    Authors & editors: [39]Robert Nemiroff ([40]MTU) & [41]Jerry Bonnell
                                 ([42]UMCP)
          NASA Official: Phillip Newman [43]Specific rights apply.
              [44]NASA Web Privacy Policy and Important Notices
                A service of: [45]ASD at [46]NASA / [47]GSFC,
                         [48]NASA Science Activation
                           & [49]Michigan Tech. U.

References

   1. https://apod.nasa.gov/apod/archivepix.html
   2. https://apod.nasa.gov/apod/image/2401/SarArcNz_McDonald_2048.jpg
   3. https://www.instagram.com/tristianmcdonaldphotography/
   4. https://www.mtu.edu/physics/department/faculty/lewis/
   5. https://www.mtu.edu/physics/
   6. https://www.windows2universe.org/glossary/aurora_SARARC.html
   7. https://www.instagram.com/p/C0e1DEXPQzR/
   8. https://apod.nasa.gov/apod/ap231111.html
   9. https://youtu.be/DLxQsUAXKag
  10. https://en.wikipedia.org/wiki/New_Zealand
  11. https://en.wikipedia.org/wiki/Geomagnetic_storm
  12. https://spaceweatherarchive.com/2021/11/22/3308/
  13. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015JA021722
  14. https://science.nasa.gov/science-research/planetary-science/earths-magnetosphere/
  15. https://physics.stackexchange.com/questions/385388/even-if-molten-iron-is-ionized-spins-how-does-it-make-a-mag-field
  16. https://spaceplace.nasa.gov/menu/earth/
  17. https://apod.nasa.gov/apod/ap000318.html
  18. https://en.wikipedia.org/wiki/Ring_current
  19. https://science.nasa.gov/heliophysics/focus-areas/magnetosphere-ionosphere/
  20. https://apod.nasa.gov/apod/ap160731.html
  21. https://en.wikipedia.org/wiki/Ion
  22. https://science.nasa.gov/earth/10-things-to-know-about-the-ionosphere/
  23. https://apod.nasa.gov/apod/ap230730.html
  24. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022GL101205
  25. https://allthingslearning.files.wordpress.com/2011/10/dogs_surprised.jpg
  26. https://apod.nasa.gov/apod/ap230927.html
  27. https://eos.org/research-spotlights/from-sar-arc-to-steve-an-atmospheric-evolution
  28. https://apod.nasa.gov/apod/ap240102.html
  29. https://apod.nasa.gov/apod/archivepix.html
  30. https://apod.nasa.gov/apod/lib/apsubmit2015.html
  31. https://apod.nasa.gov/apod/lib/aptree.html
  32. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  33. https://apod.nasa.gov/apod/calendar/allyears.html
  34. https://apod.com/feed.rss
  35. https://apod.nasa.gov/apod/lib/edlinks.html
  36. https://apod.nasa.gov/apod/lib/about_apod.html
  37. https://asterisk.apod.com/discuss_apod.php?date=240103
  38. https://apod.nasa.gov/apod/ap240104.html
  39. http://www.phy.mtu.edu/faculty/Nemiroff.html
  40. http://www.phy.mtu.edu/
  41. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  42. http://www.astro.umd.edu/
  43. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
  44. https://www.nasa.gov/about/highlights/HP_Privacy.html
  45. https://astrophysics.gsfc.nasa.gov/
  46. https://www.nasa.gov/
  47. https://www.nasa.gov/centers/goddard/
  48. https://science.nasa.gov/learners
  49. http://www.mtu.edu/