Omega Nebula
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 . 
<triplet> Omega Nebula <subj> H II region <obj> instance of <subj> Sagittarius <obj> constellation <triplet> Sagittarius <subj> constellation <obj> instance of