The Omega Nebula (Messier Object 17 or NGC 6618) is also called the Swan Nebula, the Horseshoe Nebula or (particularly south of the equator) the Lobster Nebula. It is a region of star formation and shines by excited emission casued by the higher radiation of young stars. Star formation is either still active in this nebula, or very recently ceased. A small cluster of about 35 bright but obscured stars seems embedded in the nebulosity.
(Canon EOS20D, f/6.3 Focal Reducer/Field Flattener, Meade 12" LX90 GPS, Jim W. Coleman, Port Orchard, Washington)