I feel like you have two things floating so maybe some ground for the canon and the shortness of distance bothers me just because it makes it hard to tell where exactly the canon is, because it doesn't look like it's on earth.
I kind of thought that the giant moon would look really cool on a t-shirt, but okay I will shrink it down a bit for the next version and maybe add some ground like sunhawk suggested. thanks for the suggestions everyone!