﻿ 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/