Snapped this pic the other day. At first, I was drawn by the subtlety of the central tip of the cloud, which is illuminated by reflected light from the sunlit mound of cloud between it and us, but I was wowed by these fanlike structures in the sky above the cloud. Those are not digital artifacts or anything, they are naked-eye effects. They are some sort of shadow, cast over the top of the cloud by the sun. I don't quite understand what phenomenon has created them though. Any takers?