The Checkmark Nebula, aka the Omega Nebula, aka the Horseshoe Nebula, M-17 (NGC-6618)

This beautiful diffuse nebula is shaped rather like a "2" with a wide, bright streak for the bottom. This streak stands out not only because of its brightness but because it is "suddenly there" instead of gradually fading into the background. A quiet sprinkling of stars below the nebula explains its listing as an open cluster, too. This is probably the second most distinctive diffuse nebula (and also my first sketch). Note the subtle variations of brightness at the base. Radio source.

NGC: 6618
OTHER NAMES: M-17, Checkmark, Omega or Horseshoe Nebula
CLASS: diffuse nebula / open cluster
SIZE: 46' x 37'
NUMBER OF STARS: ~ 3 dozen
DISTANCE: 3250 light years
POSITION: 18h 18m -16d 11'
DATE OF SKETCH: 08/27/76