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