There are over 150 Globular Star Clusters found inside the Milky Way Galaxy. Larger galaxies can have even more, with Andromeda Galaxy containing more than 500, and Galaxy Messier 87 a staggering 13,000. These star clusters contain hundreds of thousands of densely packed stars and form a spherical cluster due to the gravitational relationship with one another. Little is known about Globular Clusters with relation to how they were formed. There is debate over whether the stars were all formed at the same time, or whether stars were acquired somehow over many generations of stars and hundreds of millions of years. The theories on formation even change from one star cluster to another, but similarities can be drawn between them. Most contain older yellow stars and very few young hot stars, which suggest that the stars in a cluster were formed around the same time, and that there is no known Globular Star Cluster with active star formation, which does lead to a belief that they are indeed some of the oldest objects in the galaxy.
Messier 13, is one of the largest and most beautiful of these clusters seen from the Northern Hemisphere. It was originally discovered by Edmond Halley in 1714 and cataloged by Charles Messier in 1764. Messier 13 is found within the constellation of Hercules, and located at an estimated distance of 25,000 light years away. It has a diameter of almost 150 light years, and an apparent size in the night sky of 20 arc-minutes or about 2/3 the diameter of the full moon. Because this object is relatively small I pushed the limits on my Astrotrac tracking mount and shot at a 600mm focal length with one minute exposures. This exposure length did result in some tracking error, so out of about 200 images, I was only able to keep 107 that displayed tack sharp focus without any star trails.
Also of interest in this image are two small galaxies slightly to the right and above the cluster. One is easily seen in this image and it is designated as NGC 6207 and located about 30 million light years away. The second galaxy is found in between NGC 6207 and Messier 13 and called IC 4617, at a distance that I was unable to locate.
Canon Rebel T5i (Modified), Canon 300mm f2.8is II + Canon 2.0x TCIII (600mm) , f5.6, 60 second exposures (107 for a total of 107 minutes exposure), ISO 1600, Astrotrac, PixInsight, Photoshop, Lightroom. Dark, Bias and Flat Frames taken for calibration.