The Trifid Nebula (M20, NGC 6514) is located 5.400 lightyears away in the Sagittarius arm of our galaxy. It was first described by Charles Messier, who had seen the star clusters M20 and M21 in 1764, "enveloped in nebulosity". William Herschel described the region in 1784 as “three nebulae, faintly joined, that form a triangle”. The name Trifid Nebula was first used by John Herschel in 1833.
The red emission nebula is energised by the O star HD 164492A and trisected by obscuring dust lanes (Barnard B85). A blue reflection nebula surrounds the Supergiant star HD 164514. The open cluster M21 (NGC 6531) is approximately 3.800 lightyears away and is not related to the Trifid Nebula.