M20, the Trifid Nebula

Charles Messier discovered this object on June 5, 1764, and described it as a cluster of stars of 8th to 9th magnitude, enveloped in nebulosity.

The Trifid Nebula M20 is famous for its three-lobed appearance. This may have caused William Herschel, who normally carefully avoided to number Messier's objects in his catalog, to assign four different numbers to parts of this nebula: H IV.41 (cataloged May 26, 1786) and H V.10, H V.11, H V.12 (dated July 12, 1784). That he numbered this object at all may have its reason in the fact that Messier merely described it as `Cluster of Stars'. The name `Trifid' was first used by John Herschel to describe this nebula.

The dark nebula which is the reason for the Trifid's appearance was cataloged by Barnard as Barnard 85 (B 85).