M17 - The "Swan Nebula" in Sagittarius SBIG ST-4000XCM 13x15min Imager Temp -10C APM/TMB 130/780 Field Flattener 15% Crop for Composition North is down in this image M17 (NGC 6618, Swan Nebula, Omega Nebula, or Lobster Nebula for those down under) is an emission nebula located 6000 light years distant in the constellation Sagittarius. The nebula is about 15 light years across and is situated in an interstellar cloud spanning 40 light years. The nebula is 800 solar masses - much larger than M42 in Orion. The gas of M17 is illuminated by an obscured open cluster comprised of 35 stars, however, star formation is just ending in this cluster.