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.

                               2025 August 14
    [2]See Explanation. Clicking on the picture will download the highest
                        resolution version available.

                 M13: The Great Globular Cluster in Hercules
                Image Credit & [3]Copyright: [4]R. Jay Gabany

   Explanation: [5]In 1716, English astronomer [6]Edmond Halley noted,
   "This is but a little Patch, but it shews itself to the naked Eye, when
   the Sky is serene and the Moon absent." [7]Of course, M13 is now less
   modestly recognized as the Great Globular Cluster in Hercules, one of
   the brightest [8]globular star clusters in the northern sky. Sharp
   telescopic views like this one reveal the spectacular cluster's
   [9]hundreds of thousands of stars. At a distance of 25,000 light-years,
   the [10]cluster stars crowd into a region 150 light-years in diameter.
   [11]Approaching the cluster core, upwards of 100 stars could be
   contained in a cube just 3 light-years on a side. For comparison with
   our neighborhood of the Milky Way, the [12]closest star to the Sun is
   over 4 light-years away. Early telescopic observers of the great
   globular cluster also noted a curious convergence of three dark lanes
   with a spacing of about 120 degrees, seen here just below the cluster
   center. [13]Known as the propeller in M13, the shape is likely a
   [14]chance optical effect of the distribution of stars viewed from our
   perspective against the dense cluster core.

                     Tomorrow's picture: pixels in space
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    Authors & editors: [26]Robert Nemiroff ([27]MTU) & [28]Jerry Bonnell
                                 ([29]UMCP)
          NASA Official: Amber Straughn [30]Specific rights apply.
            [31]NASA Web Privacy, [32]Accessibility, [33]Notices;
                A service of: [34]ASD at [35]NASA / [36]GSFC,
                         [37]NASA Science Activation
                           & [38]Michigan Tech. U.

References

   1. https://apod.nasa.gov/apod/archivepix.html
   2. https://apod.nasa.gov/apod/image/2508/lrg_ngc6205.jpg
   3. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
   4. http://www.cosmotography.com/index.html
   5. http://messier.seds.org/xtra/similar/halley_pt.html
   6. http://www.bbc.co.uk/history/historic_figures/halley_edmond.shtml
   7. http://messier.seds.org/m/m013.html
   8. http://en.wikipedia.org/wiki/Globular_cluster
   9. https://skyandtelescope.org/observing/gobs-of-globs-guide-to-16-spring-globular-clusters/
  10. https://hubblesite.org/contents/news-releases/2008/news-2008-40.html
  11. https://apod.nasa.gov/apod/ap031213.html
  12. https://apod.nasa.gov/apod/ap160825.html
  13. https://www.cosmotography.com/images/small_ngc6205.html
  14. https://apod.nasa.gov/apod/ap231120.html
  15. https://apod.nasa.gov/apod/ap250813.html
  16. https://apod.nasa.gov/apod/archivepix.html
  17. https://apod.nasa.gov/apod/lib/apsubmit2015.html
  18. https://apod.nasa.gov/apod/lib/aptree.html
  19. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  20. https://apod.nasa.gov/apod/calendar/allyears.html
  21. https://apod.com/feed.rss
  22. https://apod.nasa.gov/apod/lib/edlinks.html
  23. https://apod.nasa.gov/apod/lib/about_apod.html
  24. https://asterisk.apod.com/discuss_apod.php?date=250814
  25. https://apod.nasa.gov/apod/ap250815.html
  26. http://www.phy.mtu.edu/faculty/Nemiroff.html
  27. http://www.phy.mtu.edu/
  28. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  29. http://www.astro.umd.edu/
  30. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
  31. https://www.nasa.gov/about/highlights/HP_Privacy.html
  32. https://www.nasa.gov/general/accessibility/
  33. https://www.nasa.gov/privacy/
  34. https://astrophysics.gsfc.nasa.gov/
  35. https://www.nasa.gov/
  36. https://www.nasa.gov/centers/goddard/
  37. https://science.nasa.gov/learners
  38. http://www.mtu.edu/