Nice going Pat, looks like you have a real battle with light pollution there mate. You've still managed some good detail, and a very low noise image, well done! Mate if your interested there is tutorial for using photoshop to remove gradients like the one you have here. I don't use it any more because pixinsight has a better tool for achieving that, but I have had some good results in the past by using it. I'll post the link below.
https://www.youtube.com/watch?v=yTEVMH_WE80