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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 April 13
    [2]See Explanation. Clicking on the picture will download the highest
                        resolution version available.

                     A Sailing Stone across Death Valley
                        Image Credit: [3]Keith Burke

   Explanation: How did this big rock end up on this strange terrain? One
   of the more unusual places here on [4]Earth occurs inside [5]Death
   [6]Valley, [7]California, [8]USA. There a dried lakebed named
   [9]Racetrack Playa exists that is almost perfectly flat, with the odd
   exception of some very large stones, one of which is pictured here in
   April of 2019 beneath a dark, [10]Milky-Way filled sky. Now the
   [11]flatness and texture of large playa like [12]Racetrack are
   fascinating but not [13]scientifically puzzling -- they are caused by
   mud flowing, drying, and cracking after a heavy rain. Only recently,
   however, has a [14]viable scientific hypothesis been given to explain
   how heavy [15]sailing stones end up near the middle of such a large
   flat surface. Unfortunately, as frequently happens in science, a
   seemingly [16]surreal [17]problem ends up having a [18]relatively
   mundane solution. [19]It turns out that in winter thin ice sheets form,
   and winds push ice sections laden with [20]even heavy rocks across the
   temporarily slick playa when sunlight melts the ice.

                     Tomorrow's picture: garbled galaxy
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    Authors & editors: [32]Robert Nemiroff ([33]MTU) & [34]Jerry Bonnell
                                 ([35]UMCP)
          NASA Official: Phillip Newman [36]Specific rights apply.
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                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/2004/SailingStone_Burke_1366.jpg
   3. mailto:%20keith%20.dot.%20d%20.dot.%20burke%20@at@%20Hotmail%20.dot.%20com
   4. https://solarsystem.nasa.gov/planets/earth/overview/
   5. https://en.wikipedia.org/wiki/Death_valley
   6. https://www.youtube.com/watch?v=G6xq2z3v8JQ
   7. https://en.wikipedia.org/wiki/California
   8. https://www.cia.gov/library/publications/the-world-factbook/geos/us.html
   9. https://www.youtube.com/watch?v=tf8t0eo3cLQ
  10. https://apod.nasa.gov/apod/ap191015.html
  11. https://apod.nasa.gov/apod/ap191022.html
  12. https://www.nps.gov/deva/planyourvisit/the-racetrack.htm
  13. http://epod.usra.edu/blog/2006/06/racetrack-playa.html
  14. https://ui.adsabs.harvard.edu/abs/2014ESuDD...2.1005L/abstract
  15. https://en.wikipedia.org/wiki/Sailing_stones
  16. https://upload.wikimedia.org/wikipedia/commons/8/8b/Salvador_Dali_A_%28Dali_Atomicus%29_09633u.jpg
  17. http://www.desertusa.com/mag99/july/stories/race1.html
  18. https://catsareontop.com/wp-content/uploads/2018/01/bored-feature.jpg
  19. https://scripps.ucsd.edu/news/mystery-solved-sailing-stones-death-valley-seen-action-first-time
  20. http://www.youtube.com/watch?v=u1hoiHvOeGc
  21. https://apod.nasa.gov/apod/ap200412.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=200413
  31. https://apod.nasa.gov/apod/ap200414.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/