M 17 is an emission nebula. Interstellar hydrogen has been
ionized and caused to glow by a cluster of stars embedded in and
hidden by the nebula. Darker areas of gas and dust obscure part
of this lit-up cloud, giving the nebula its distinct shape. It
is sometimes called the "horseshoe", or "omega", or "lobster" nebula;
but it is most commonly known as the "swan nebula". It is about 6800
light years away, in the same general area as M 16. There is enough
material in M 17 to make 800 suns.

Image data:
Camera: Canon 350XT (modified)
Exposure: ISO 800, 5 minutes x 29
Telescope: 10" Schmidt-Newtonian, Baader coma corrector