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 March 19
    [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]Eric Coles and [5]Mel Helm

   Explanation: [6]In 1716, English astronomer [7]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." [8]Of course, M13 is now less
   modestly recognized as the Great Globular Cluster in Hercules, one of
   the brightest [9]globular star clusters in the northern sky. Sharp
   telescopic views like this one [10]reveal the spectacular cluster's
   hundreds of thousands of stars. At a distance of 25,000 light-years,
   the [11]cluster stars crowd into a region 150 light-years in diameter.
   [12]Approaching the cluster core upwards of 100 stars could be
   contained in a cube just 3 light-years on a side. For comparison, the
   [13]closest star to the Sun is over 4 light-years away. The remarkable
   range of brightness recorded in this image follows stars into the dense
   cluster core and reveals three subtle dark lanes forming the apparent
   shape of a propeller just below and slightly left of center. Distant
   background galaxies in the medium-wide field of view include NGC 6207
   at the upper left.

                   Tomorrow's picture: when night/day = 1
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    Authors & editors: [25]Robert Nemiroff ([26]MTU) & [27]Jerry Bonnell
                                 ([28]UMCP)
          NASA Official: Phillip Newman [29]Specific rights apply.
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                A service of: [31]ASD at [32]NASA / [33]GSFC
                           & [34]Michigan Tech. U.

References

   1. https://apod.nasa.gov/apod/archivepix.html
   2. https://apod.nasa.gov/apod/image/2003/Messier13_HelmColes.jpg
   3. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
   4. http://www.astrobin.com/users/coles44/
   5. https://pbase.com/melhelm/image/165897126
   6. http://messier.seds.org/xtra/similar/halley_pt.html
   7. http://www.bbc.co.uk/history/historic_figures/halley_edmond.shtml
   8. http://messier.seds.org/m/m013.html
   9. http://en.wikipedia.org/wiki/Globular_cluster
  10. https://skyandtelescope.org/observing/m13-and-galaxies/
  11. http://heritage.stsci.edu/2008/40/caption.html
  12. https://apod.nasa.gov/apod/ap031213.html
  13. https://apod.nasa.gov/apod/ap160825.html
  14. https://apod.nasa.gov/apod/ap200318.html
  15. https://apod.nasa.gov/apod/archivepix.html
  16. https://apod.nasa.gov/apod/lib/apsubmit2015.html
  17. https://apod.nasa.gov/apod/lib/aptree.html
  18. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  19. https://apod.nasa.gov/apod/calendar/allyears.html
  20. https://apod.nasa.gov/apod.rss
  21. https://apod.nasa.gov/apod/lib/edlinks.html
  22. https://apod.nasa.gov/apod/lib/about_apod.html
  23. http://asterisk.apod.com/discuss_apod.php?date=200319
  24. https://apod.nasa.gov/apod/ap200320.html
  25. http://www.phy.mtu.edu/faculty/Nemiroff.html
  26. http://www.phy.mtu.edu/
  27. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  28. http://www.astro.umd.edu/
  29. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
  30. https://www.nasa.gov/about/highlights/HP_Privacy.html
  31. https://astrophysics.gsfc.nasa.gov/
  32. https://www.nasa.gov/
  33. https://www.nasa.gov/centers/goddard/
  34. http://www.mtu.edu/