The Omega Nebula, also known as the Swan Nebula, Checkmark Nebula, and the Horseshoe Nebula (catalogued as Messier 17 or M17 or NGC 6618) is an H II region in the constellation Sagittarius. It is located near some of the richest starfields of the Milky Way, and is in the northern two-thirds of Sagittarius.

The Omega Nebula is located 5,500 light-years from Earth and is quite large and massive as it contains roughly 1000 times the mass of our Sun. The bright central region is about 15 light years across.

This nebula is rated a 6 in magnitude and you can see it through a pair of binoculars in a dark area far away from the city lights.