It receives another triple R, with magnitude 16 stars. Image from the Digital Sky Survey. Map Printable Map More info. Indeed the more northerly cluster lies only 39' away from the edge of the Lagoon's nebulosity. Dreyer's estimate that the cluster consisted of magnitude 20 stars is grossly overstated.
More recent estimates yield mag.
Image from the Digital Sky Survey. Map Printable Map More info. Dreyer describes it as pretty rich with little central condensation. Overall magnitude is 5.9, size is 13', stars estimated from mags. This extract from the Digital Sky Survey shows M21 in the upper left, the Trifid in the lower right.