When I first saw this it was nearly horizontal, and looked, if not a flying saucer, then at least like a flying plate viewed edge on. It's a distant sunlit contrail, often mistaken for UFOs, space junk, or meteors. So I thought it would be useful to get a sequence of photos and video at different zoom levels.
The video above is unedited, zooming from 24mm to 2000mm.
The sequence of photos are all straight from the camera, except the first where I've called out the trail as it's hard to see.
Finally some digital zoom: