Clear skies on a full moon night? No problem!

I wanted to try the capturing and processing of a globular star cluster for the first time... coincidentally we had clear sky during a 100% full moon night so I thought it was worth giving it a try

This is the first time that I stacked different exposure times and also combined different stretches (to handle the high dynamic range of this object). I think I found a good balance between core exposure and fainter outer stars. I am satisfied with how it turned out... only the spikes and colors of the dominant stars could be improved. Let's see how I can work on that in the future 

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The Hercules globular cluster is the brightest cluster on northern skies (mag 5.8 at 25.000 ly distance). It contains approximately 500.000 stars within a diameter of 150 ly. As most globular cluster, it contains many old "red" stars with low metallicity. Such "population II" stars have been formed in the early universe. Since heavy elements only came to light over the course of billions of years (e.g. via supernovae), only the "recycled" newer stars will shows such elements in their spectrum.
The stars within a globular cluster are gravitationally bound and will most likely never leave their system. (Stars in "open star clusters" on the other hand will drift away at some point. That's the reason why we mostly observe young stars in such clusters.) A globular cluster is usually located in a galaxy-halo and is gravitationally bound to this galaxy. The Milkyway contains ~150, Andromeda ~500 and M87 up to 10.000 globular clusters.

M13 was discovered by Halley in 1714, and cataloged by Messiers in 1764. Wikipedia states, that one of the first pictures was actually taken in 1891 by Julius Scheiner with the help of "Der Große Refraktor" in Potsdam. That would be awesome because I frequently visited this refractor as a student  But wikipedia also states that the refractor wasn't installed until 1899 so I guess i'll never know for sure

Another interesting fact about this object is that it has been targeted with the Arecibo message. An interstellar radio message carrying basic information about humanity. The broadcast is more of a symbolic nature... despite the low resolution of the sent image, a globular cluster might not be the best choice to start searching for intelligent life. Planetary orbits are unstable because of tidal forces from lot's of chaotic drifting stars. Simulations have shown that the average planet (in 1 AU distance) would merely survive 100 Mio years.

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Revision B - zoomed version
Revision C - comparison of M13 / M3 / NGC 5466

I actually also captured M3 and NGC 5466. Because of the similarity (at least M3) I don't want to publish them as a single picture as well. Therefore, you can check them out in Revision C.