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.

                              2019 September 29
    [2]See Explanation. Clicking on the picture will download the highest
                        resolution version available.

              MyCn 18: The Engraved Hourglass Planetary Nebula
     Image Credit: [3]NASA, [4]ESA, [5]Hubble; Processing & [6]License:
                               [7]Judy Schmidt

   Explanation: Do you see the hourglass shape -- or does it see you? If
   you can picture it, the rings of [8]MyCn 18 trace the outline of an
   hourglass -- although one with an unusual eye in its center. Either
   way, the sands of time are running out for the central star of this
   hourglass-shaped [9]planetary nebula. With its [10]nuclear fuel
   exhausted, this brief, spectacular, closing phase of a [11]Sun-like
   [12]star's life occurs as its outer layers are ejected - its core
   becoming a cooling, fading [13]white dwarf. In 1995, astronomers used
   the [14]Hubble Space Telescope (HST) to make a series of images of
   [15]planetary nebulae, including [16]the one featured here.
   [17]Pictured, delicate rings of colorful glowing gas ([18]nitrogen-red,
   [19]hydrogen-green, and [20]oxygen-blue) outline the tenuous walls of
   the [21]hourglass. The unprecedented sharpness of the Hubble images has
   revealed [22]surprising details of the [23]nebula ejection process that
   are helping to resolve the outstanding mysteries of the [24]complex
   shapes and symmetries of planetary nebulas like MyCn 18.

                       Tomorrow's picture: orion treed
     __________________________________________________________________

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    Authors & editors: [36]Robert Nemiroff ([37]MTU) & [38]Jerry Bonnell
                                 ([39]UMCP)
          NASA Official: Phillip Newman [40]Specific rights apply.
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                A service of: [42]ASD at [43]NASA / [44]GSFC
                           & [45]Michigan Tech. U.

References

   1. https://apod.nasa.gov/apod/archivepix.html
   2. https://apod.nasa.gov/apod/image/1909/MyCn18_HubbleSchmidt_960.jpg
   3. https://www.nasa.gov/
   4. http://www.esa.int/
   5. https://www.nasa.gov/mission_pages/hubble/main/index.html
   6. https://creativecommons.org/licenses/by/2.0/
   7. http://geckzilla.com/
   8. https://en.wikipedia.org/wiki/Engraved_Hourglass_Nebula
   9. https://en.wikipedia.org/wiki/Planetary_nebula
  10. https://www.nasa.gov/directorates/spacetech/game_changing_development/Nuclear_Thermal_Propulsion_Deep_Space_Exploration
  11. https://solarsystem.nasa.gov/solar-system/sun/in-depth/
  12. http://www.phys.ncku.edu.tw/~htsu/humor/msblues.html
  13. https://apod.nasa.gov/apod/ap000910.html
  14. https://apod.nasa.gov/apod/ap010806.html
  15. https://apod.nasa.gov/apod/planetary_nebulae.html
  16. https://hubblesite.org/image/397/category/104-annotated-observations
  17. https://www.flickr.com/photos/geckzilla/9972784394
  18. https://periodic.lanl.gov/7.shtml
  19. http://www.youtube.com/watch?v=lFptgQ8GA_U
  20. http://education.jlab.org/itselemental/ele008.html
  21. https://en.wikipedia.org/wiki/Hourglass
  22. https://ui.adsabs.harvard.edu/abs/2000AJ....119..315D/abstract
  23. https://apod.nasa.gov/apod/ap960117.html
  24. http://faculty.washington.edu/balick/pPNe/
  25. https://apod.nasa.gov/apod/ap190928.html
  26. https://apod.nasa.gov/apod/archivepix.html
  27. https://apod.nasa.gov/apod/lib/apsubmit2015.html
  28. https://apod.nasa.gov/apod/lib/aptree.html
  29. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  30. https://apod.nasa.gov/apod/calendar/allyears.html
  31. https://apod.nasa.gov/apod.rss
  32. https://apod.nasa.gov/apod/lib/edlinks.html
  33. https://apod.nasa.gov/apod/lib/about_apod.html
  34. http://asterisk.apod.com/discuss_apod.php?date=190929
  35. https://apod.nasa.gov/apod/ap190930.html
  36. http://www.phy.mtu.edu/faculty/Nemiroff.html
  37. http://www.phy.mtu.edu/
  38. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  39. http://www.astro.umd.edu/
  40. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
  41. https://www.nasa.gov/about/highlights/HP_Privacy.html
  42. https://astrophysics.gsfc.nasa.gov/
  43. https://www.nasa.gov/
  44. https://www.nasa.gov/centers/goddard/
  45. http://www.mtu.edu/