M17 - OMEGA NEBULA

Messier 17, known by several evocative names including the Omega Nebula, Swan Nebula, Horseshoe Nebula, and Lobster Nebula, is one of the brightest and most massive star-forming regions in our galaxy. Located approximately 5,500 light-years from Earth in the constellation Sagittarius, this emission nebula spans about 15 light-years across in its brightest visible portion, though the full extent of the associated molecular cloud is vastly larger, containing enough gas to form tens of thousands of stars. The nebula's total mass is estimated at about 800 solar masses of ionized gas alone, with the surrounding molecular cloud containing perhaps 30,000 solar masses of material. M17 is illuminated by a cluster of about 35 hot, young stars hidden within its bright central bar, many of which are obscured by dust at visible wavelengths but revealed in infrared observations. M17 was discovered by Philippe Loys de Cheseaux in 1745 and independently found by Messier in 1764. The nebula gets its most common names from the shape of its brightest region, which resembles the number 2 or a swan floating on water when viewed through a telescope. For amateur astronomers, M17 is a stunning target even in binoculars, which show its characteristic hooked shape and bright surface brightness. A telescope of 4 inches or more reveals intricate structure, including the bright bar, sweeping arcs of luminous gas, and dark bays of obscuring dust. Narrowband filters enhance the view dramatically. M17 is considered second only to the Orion Nebula (M42) in terms of surface brightness among emission nebulae.

The visible nebula spans about 15 light-years with 800 solar masses of ionized gas, within a molecular cloud of 30,000 solar masses at 5,500 light-years distance.