Explanation:
In 1714,
Edmond Halley
noted that M13 "shows itself to the
naked eye when the sky is serene and the Moon absent."
Of course, M13
is now modestly recognized as
the Great Globular Cluster in Hercules,
one of the brightest
globular
star clusters in the northern sky.
Telescopic views 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,
but
approaching the cluster core
upwards of 100 stars could 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.
Along with the cluster's dense core, the outer reaches of M13
are highlighted in
this
deep color image.
A distant background galaxy,
NGC 6207
is also visible above and
to the right of the Great Globular Cluster
M13.
