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                        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.

                                2020 August 5

         IFRAME: [2]https://www.youtube.com/embed/X_UOLpUDwpU?rel=0

                          Picture Rocks Sun Dagger
   Video Credit & Copyright: Martha Schaefer, [3]Brad Schaefer, Jim Stamm;
   Music & [4]License: [5]Awakening ([6]Wojciech Usarewicz), [7]Lone Tree
                                    Music

   Explanation: Ancient sun daggers will not hurt you, but they may tell
   you the time.  A [8]sun dagger is a dagger-shaped gap in a shadow
   created by sunlight streaming through a crevice in a nearby rock.
   Starting over a thousand year ago, [9]native people of the American
   southwest carved spiral [10]petroglyphs into rocks that became
   illuminated by [11]sun daggers in different ways as the [12]Sun shifts
   in the sky. A type of [13]sundial, where the end of the [14]sundagger
   points in [15]the spiral at high noon (for example) indicates a time of
   year, possibly illuminating a [16]solstice or [17]equinox.  [18]Sun
   daggers are thought to have been used by [19]Sun Priests during lone
   vigils with prayers and offerings.  Of the few known, the [20]featured
   video discusses the historic [21]Picture Rocks Sun Dagger near
   [22]Tucson, [23]Arizona, [24]USA, likely created by a [25]Hohokam Sun
   Priest around 1000 AD.

                        Tomorrow's picture: 20 and 21
     __________________________________________________________________

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    Authors & editors: [37]Robert Nemiroff ([38]MTU) & [39]Jerry Bonnell
                                 ([40]UMCP)
          NASA Official: Phillip Newman [41]Specific rights apply.
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                A service of: [43]ASD at [44]NASA / [45]GSFC
                           & [46]Michigan Tech. U.

References

   1. https://apod.nasa.gov/apod/archivepix.html
   2. https://www.youtube.com/embed/X_UOLpUDwpU?rel=0
   3. https://www.lsu.edu/physics/people/faculty/schaefer.php
   4. https://creativecommons.org/licenses/by-nc-nd/4.0/
   5. https://www.jamendo.com/album/153742/awakening-native-american-flute-solo
   6. https://www.quora.com/profile/Wojciech-Usarzewicz
   7. https://soundcloud.com/lone-tree-music
   8. https://www2.hao.ucar.edu/Education/SolarAstronomy/sun-dagger
   9. https://kids.nationalgeographic.com/explore/native-americans/native-people-of-the-american-southwest/
  10. https://en.wikipedia.org/wiki/Petroglyph
  11. https://www.planetquest.org/learn/sundagger.html
  12. https://solarsystem.nasa.gov/solar-system/sun/overview/
  13. https://en.wikipedia.org/wiki/Sundial
  14. https://en.wikipedia.org/wiki/Fajada_Butte
  15. https://en.wikipedia.org/wiki/Fajada_Butte#/media/File:Fajadadiagram.JPG
  16. https://apod.nasa.gov/apod/ap170621.html
  17. https://apod.nasa.gov/apod/ap190320.html
  18. https://ui.adsabs.harvard.edu/abs/1979Sci...206..283S/abstract
  19. https://solsticeproject.org/Chaco_Films_Videos/The_Sun_Dagger/index.html
  20. https://www.youtube.com/embed/X_UOLpUDwpU
  21. https://apod.nasa.gov/apod/image/2008/PictureRocks_Sundagger_JAHH.pdf
  22. https://www.youtube.com/watch?v=JMNaYdIH9yw
  23. https://en.wikipedia.org/wiki/Arizona
  24. https://en.wikipedia.org/wiki/United_States
  25. https://en.wikipedia.org/wiki/Hohokam
  26. https://apod.nasa.gov/apod/ap200804.html
  27. https://apod.nasa.gov/apod/archivepix.html
  28. https://apod.nasa.gov/apod/lib/apsubmit2015.html
  29. https://apod.nasa.gov/apod/lib/aptree.html
  30. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  31. https://apod.nasa.gov/apod/calendar/allyears.html
  32. https://apod.nasa.gov/apod.rss
  33. https://apod.nasa.gov/apod/lib/edlinks.html
  34. https://apod.nasa.gov/apod/lib/about_apod.html
  35. http://asterisk.apod.com/discuss_apod.php?date=200805
  36. https://apod.nasa.gov/apod/ap200806.html
  37. http://www.phy.mtu.edu/faculty/Nemiroff.html
  38. http://www.phy.mtu.edu/
  39. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  40. http://www.astro.umd.edu/
  41. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
  42. https://www.nasa.gov/about/highlights/HP_Privacy.html
  43. https://astrophysics.gsfc.nasa.gov/
  44. https://www.nasa.gov/
  45. https://www.nasa.gov/centers/goddard/
  46. http://www.mtu.edu/