THE GREAT GLOBULAR CLUSTER IN HERCULES
Messier 13
​
The Great Globular Cluster
Messier 13 (M13), also designated the Great Globular Cluster in Hercules, is a globular cluster of about 300,000 stars in the constellation of Hercules and is one of the best-known clusters of the northern-hemisphere.
Globular clusters are spherical collections of stars that orbit a galactic core as satellites. There are about 150 to 158 currently known globular clusters in the Milky Way, with perhaps 10 to 20 more still undiscovered.
M13 is about 145 light-years in diameter and located about 25,100 light-years away from Earth.
Due to its apparent magnitude the Cluster is barely visible with the naked eye on a very clear night. Its diameter is about 23 arc minutes and it is readily viewable in small telescopes.
​
The Arecibo message of 1974, which contained encoded information about the human race, DNA, atomic numbers, Earth's position and other information, was beamed from the Arecibo Observatory radio telescope towards M13 as an experiment in contacting potential extraterrestrial civilizations in the cluster.
Image data:
​
Lens: 8" Altair Astro Imaging Newtonian Telescope, focal length: 800mm, f4 and 10" Lacerta Newton, focal length 1250mm, f5
Camera: Canon 700D (modified) + Astronomik CLS Filter + and Atik 414EX monochrome CCD + L-R-G-B Filter set.
Mount: Sky-Watcher NEQ-6 Pro SynScan GOTO + Autoguiding (PHD2)
Aquisition data: 57 min (51 min DSLR + 6 min CCD) + Calibration Images
Processing: Nebulosity 4, LightRoom, PhotoShop
​
Background Galaxies
The depicted area around M13 contains several interesting objects as well. Numerous stars in the foreground and distant galaxies in the background. Two of them are well-studied by astronomers:
NGC 6207: spiral galaxy about 39 million light years away, the diameter of the galaxy is 34,000 light years
IC 4617: spiral galaxy about 503 million light years away
Image data:
​
Lens: 8" Altair Astro Imaging Newtonian Telescope, focal length: 800mm, f4
Camera: Canon 700D (modified) + Astronomik CLS Filter
Mount: Sky-Watcher NEQ-6 Pro SynScan GOTO + Autoguiding (PHD2)
Aquisition data: 59 min (8x1min, 4x4min, 7x5min, ISO800) + Calibration Images
Processing: Nebulosity 4, LightRoom, PhotoShop
​
Collaborative Astrophotography
The M13 was the first image project of an astrophotographic collaboration. The CCD images were made by Dr. Tobias Bösing with a 10 inch newtonian telescope on 1250 mm focal length. Combined with images on 800 mm it resulted in a much more detailed depiction of the individual stars within the cluster. Beside the better resolution the colours of the stars can be significantly better recognised in the combined image.
