Explanation:
M13 is
modestly recognized as
the Great Globular Cluster
in Hercules.
A system of stars numbering in the hundreds of thousands,
it is one of the brightest
globular
star clusters in the northern sky.
At a distance of 25,000 light-years, the cluster stars
crowd
into a region 150 light-years in diameter, but
approaching the cluster core
over 100 stars would be contained
in a cube just 3 light-years on a side.
For comparison, the
closest star to the Sun is over
4 light-years away.
This stunning view of the cluster combines recent telescopic
images of the cluster's dense core with
digitized photographic plates recorded between 1987 and 1991
using the Samuel Oschin Telescope, a wide-field
survey instrument at Palomar Observatory.
The resulting composite highlights both inner and outer reaches
of the giant star cluster.
Among the distant background galaxies also visible,
NGC
6207
is above and to the left of the Great Globular Cluster
M13.
