Messier 13, also designated NGC 6205 and sometimes called the Great Globular Cluster in Hercules or the Hercules Globular Cluster, is a globular cluster of about 300,000 stars in the constellation of Hercules.

M13 was discovered by Edmond Halley in 1714, and catalogued by Charles Messier on June 1, 1764.

With an apparent magnitude of 5.8, it 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.

M13 is about 145 light-years in diameter, and it is composed of several hundred thousand stars, the brightest of which is a red giant, the variable star V11, with an apparent visual magnitude of 11.95. M13 is 25,100 light-years away from Earth.

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. While the cluster will move through space during the transit time, the proper motion is small enough that the cluster will only move 24 light years, only a fraction of the diameter of the cluster. Thus, the message will still arrive near the center of the cluster. [Source: Wikipedia]

The image was captured with the venerable Meade 12"LX200, using the Atik 383L+ mono at F7.16 (i.e. 2182mm FL). Astronomik's Luminance, Red, Green and Blue filters were used. Subs were taken at 1x1 bin, -10C, and 90 seconds each for L, R, G and B.

Image 2016 --

Lum 90s: 69 subs (1.73 hr) on Jun 20th and 21st.

Red 90s: 34 subs (0.85 hr) on Jun 20th and 21st.

Green 90s: 35 subs (0.88 hr) on Jun 20th and 21st.

Blue 90s: 34 subs (0.85 hr) on Jun 20th and 21st.

Processing was done with PixInsight, following (for the most part) kayronjm's tutorial of Feb. 24th, 2013. Filter L was used to develop the Lum image. R, G and B were collected for the color mix. North is up, and this is a slight crop due to the misalignment from dithering.

This is really my first try with a globular cluster. Processing probably could have been better.

EDIT JUL 1, 2016:

Image 2016 --

Lum 10s: 54 subs (0.15 hr) on Jun 29th.

Lum 300s: 21 subs (1.75 hr) on Jun 29th.

Used Pixinsight HDR Composition process to combine the original 90s exposures with the 10s and 300s. Image came out a bit better, but not my best.