Imaged on April 4th and 8th, 2016 at the Danville Conservation Area (New Florence, Missouri) with a SBIG ST-8300M on an Astro-Tech AT90EDT at f/6.7 603mm.
LRGB – https://www.flickr.com/photos/dcrowson/26627906420/sizes/l
M4 (NGC 6121) is a Shapley-Sawyer class IX (http://en.wikipedia.org/wiki/Shapley%E2%80%93Sawyer_Concentration_Class) globular cluster located approximately 7,200 light-years away in Scorpius. It is easy to find in the sky because it is just over a degree away from the bright (magnitude ~1) star Antares (bottom right in the image).
NGC 6144 is the class XI globular at the top right.
Luminance â€“ 12x600s â€“ 120 minutes â€“ binned 1×1
RGB â€“ 8x300s â€“ 40 minutes each â€“ binned 2×2
240 minutes total exposure â€“ 4 hours