¿ 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 __________________________________________________________________ [26]< | [27]Archive | [28]Submissions | [29]Index | [30]Search | [31]Calendar | [32]RSS | [33]Education | [34]About APOD | [35]Discuss | [36]> __________________________________________________________________ Authors & editors: [37]Robert Nemiroff ([38]MTU) & [39]Jerry Bonnell ([40]UMCP) NASA Official: Phillip Newman [41]Specific rights apply. [42]NASA Web Privacy Policy and Important Notices 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/