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Thanks, Naomi. It's difficult to estimate size without knowing distance. Did it continue in a straight line until the horizon? Any sound, smoke, lights? The only one I ever saw, a couple of years ago was black, apparently spherical and moved steadily over my back garden and when I went to the front there was no sign of it. Possibly the size of a car. I would have guessed a couple of hundred feet high, but impossible to be sure about that. I presumed it might be some kind of drone, but no noise, no lights, no manoeuvres. The oddest thing I have seen. But nothing concrete to pin down. I'd love to know what it was.