Messier 18 is an open cluster in Sagittarius but in that part of the sky we don’t just get the cluster. We get some nearby hydrogen glow in the top left and the hint of some dark dust throughout the frame.

I’m not sure if that blue “glow” around the cluster is really nebulosity. It might be glare – maybe reflections from the bright stars in the telescope, but it also might be nebulosity. I’m not really sure. It doesn’t really show any structure but is just a blue glow and that makes me suspicious. But, I’m giving it the benefit of the doubt because there is some hydrogen glow in there and there is so much dust in the region that the blue glow might be reflection nebulosity.

The cluster itself is about 4,900 light years from Earth. It’s age is estimate at about 300 million years.

For all the technical details, see astrobin.