The Omega Nebula (nicknamed the Swan Nebula) is an H II region in the constellation of Sagittarius. It is about 5,500 light-years away from Earth. It was discovered by Philippe Loys de Chéseaux in 1745. Charles Messier added it to his catalog as M17 on the night of 3 June 1764. M17 has more names than any other deep-sky object. In addition to the Omega Nebula and Swan Nebula, it is also called the Horseshoe Nebula, the Checkmark Nebula and the Lobster Nebula. Omega can be seen through binoculars or a small telescope.
- Nigel Henbest; Heather Couper, The Guide to the Galaxy (New York: Press Syndicate of the University of Cambridge, 1994), p. 209
- Robert Thompson; Barbara Thompson, Illustrated Guide to Astronomical Wonders: From Novice to Master Observer (Sebastopol, CA: Make:Books, 2007), p. 407
- Philip S. Harrington; Edward Pascuzzi, Astronomy for All Ages: Discovering the Universe Through Activities for Children and Adults (Guilford, CT: Globe Pequot Press, 2000), p. 153