Taken from Greenwich Royal Observatory, all photos processed with Darktable and stitched together with Hugin, great open source projects for image processing.
I think It is important to use manual mode when taking pictures for a panorama. This way you can ensure a coherent exposure between all of them. Some stitching programs have auto exposure correction, but I don’t usually like the results. I’d rather concentrate in processing one of the photos, and apply the same processing to the remaining ones. And after that, pass all of them to the photo stitching program.