I have to ask though, what's a "comet mode"? I have never heard of it. I believe what Scott was asking was how did you get the the end of the star trails to look like a big dot?
Really nice shot! I definitely prefer the pano crop here. The only thing I would fix is the bright horizon area that buldges over the group of trees on the right. It should remain flat across the horizon instead of following the tree silhouette. Other then that, great job!
