@keeptrying Thanks, Linda: it’s basically a polar coordinate transform: you can do it in Photoshop, but I used an app on my phone, which also seems to have introduced an overlap and some fading of the ends of the original image.
@clifford Thanks, Cliff. Yes, it’s a nice effect. The app has hidden the join much better than I would have done in PS, and the fade does give an impression of rotation: a little meteorite heading towards us.
