M18 (NGC 6613) -- Open Cluster in Sagittarius
The Black Swan
It is a curse to be close to the Swan Nebula (M17), one of the most impressive deep sky objects
in the heavens. About one-degree south of the Swan Nebula is a nice but small gathering of
stars (M18). Since it is a Messier Object it is observed but often only long enough to check it off
the Messier List before returning to marvel at M17. I fully understand, but if you do have the time,
spend a little time on this Open Cluster – it has a charm all its own.
A double star marks its center while a partial curve of brighter stars forms an arc around them.
The cluster is embedded in the thick background stars of the Milky Way, so where the cluster
ends, and the background stars begin is not obvious.
Stephen O’Meara calls this cluster the “Black Swan” in his book the Messier Objects. I like the
name since it reflects it close association to the Swan Nebula, even though I fail to see the
swan-like form in the arrangement of stars as he does. Maybe you will have better luck.