                        Astronomy Picture of the Day

    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

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

   Explanation: In 1716, English astronomer 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." Of course, M13 is now less modestly
   recognized as the Great Globular Cluster in Hercules, one of the
   brightest globular star clusters in the northern sky. Sharp telescopic
   views like this one reveal the spectacular cluster's hundreds of
   thousands of stars. At a distance of 25,000 light-years, the cluster
   stars crowd into a region 150 light-years in diameter. 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 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. Known as the
   propeller in M13, the shape is likely a 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: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Amber Straughn Specific rights apply.
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