Constellation: Sagittarius
Distance: 5000 - 6000 light years
Magnitude: 6
Actual Size: 40 light years across
Visual Size: 11 arcminutes
Other Designations: NGC6618

Messier 17 was discovered by Philippe Loys de Chéseaux in 1745, but was independantly discovered by Charles Messier on 3rd June 1764 and added to his catelogue.  The nebula is known by several names - Omega Nebula, Swan Nebula and the Lobster Nebula.

This area of the sky is a region of star formation.  The nebula shines because of the high energy radiation of the young stars in the area.  The stars themselves are hidden from view by the surrounding gas.

The mass of the gas within the nebula has been estimated to be about 800 times that of our Sun, which is considerably more than the Great Orion Nebula (Messier 42.)