M20 (The Trifid Nebula, NGC 6514, Sh2-30 and others) is a large emission (bottom portion) and reflection (top portion) nebula located approximately 5,200 light-years away in Sagittarius.
M21 (NGC 6531 and others) is a trumpler (https://en.wikipedia.org/wiki/Trumpler_classification) class I 3 m open cluster located approximately 3,900 light-years away.
Luminance – 12x600s – 120 minutes – binned 1x1
RGB – 8x300s – 40 minutes each – binned 2x2
240 minutes total exposure – 4 hours
Imaged on September 6th and 8th, 2021 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/51443469521/sizes/l/
I have a closer image of M20 taken at Danville here - https://www.flickr.com/photos/dcrowson/7627067670.
This is image will be panel three of four for a mosaic of the area.