Scutum A grand, fan-shaped cluster, with a bright star at the apex. Dark structures to the south. M 11 is the finest open cluster north of -40 degrees for larger instruments. Very rich and compact, it has a bright star near its center. Here as in M 4 we get the impression of dark lanes crossing the cluster.
Common examples are the Great Orion Nebula and the Lagoon Nebula.
The classic Horsehead Nebula is an example of a dark obscuring nebula. These nebulae are probably areas of recent activity and great heat. A 3-inch easily shows the nebula and cluster but not the lane. Very nice in a 10-inch at 80x. Sagittarius is the Horseshoe or Omega Nebula.