The Great Cluster in Hercules

Messier 13 - The Great Globular Star Cluster in the Constellation Hercules - Credit: Data obtained from 'The Autonomous Telescope' - Open University. Pirate Telescope a 17" PlaneWave CDK17 telescope with a FLI PL16803 CCD detector on Mount Teide

Our Galaxy - The Milky Way - has a retinue of satellite globular star clusters which sit within the galactic halo.  There are about 150 known globular star clusters gravitationally linked to the Milky Way.  A globular star cluster is a spherical collection of stars bound together by gravity. The distance between stars at their cores is measured in a few light years and anyone living on a planet orbiting one of them would have a night sky full of bright stars. The stars that make up globular clusters are very old and metal poor (comprised from Hydrogen and Helium and precious little else).

From the Earth's northern hemisphere and using little more than 10x40 binoculars, The Great Globular Cluster in Hercules is visible as a circular misty patch.  M13 has approximately 300,000 stars, arranged in a sphere with a diameter of 145 light years and is 25,100 light years distant from our Solar System.

In the 1970s the Arecibo Radio Telescope was used to send a signal announcing mankind's presence out towards the centre of the Great Globular Star Cluster.  If our species is still in existence we might receive a reply in 50,150 years time!

I  have always enjoyed looking through my telescope eye-piece at these ancient collections of stars. They are almost as old as the Universe itself, they are located far away in our Galaxy's suburbs, simultaneously - both massive and ephemeral in the dark night sky.

"Twinkle, twinkle sphere of  light

How I wonder at the sight

Above the disk of our Milky Way

Both cosmic close and far away

Twinkle, twinkle ball of light

Ancient starlight in the night"