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NOTE: OK, here's one for you to ponder. I've been thinking about this video for the past 24 hours and decided to post for comment. Personally, I think it is a balloon type object...but who knows. A comment with graphs (below) on ATS probably explains the object best. What's your opinion? Lon
From ATS forum: I would feel inclined to say that it's likely a balloon, because of the way it moves, except that when I took a closer look at the video it seems impossible for any non-changing shape to "rotate" in such a way.
Try this yourself. Watch the video again and pause it whenever it looks like it could be a 3-dimensional shape (like a donut or whatever else). Try to think of all possible shapes that could produce that silhouette you're seeing. The closest thing I could think of is an hourglass shape with a wide hole going through it, and two thin arms going down the outside of it (click graph to enlarge):
If you keep that shape in your head while you watch it, it seems possible. But then there are times when this shape seems to rotate from one side to the other without ever showing the hole in the middle, which would be physically impossible.
The only other thing I could think of, and of course this is entirely hypothetical, would be some kind of craft meant to be completely invisible to viewers below, but which is either malfunctioning or is still in the prototype stage. The basic principle for artificial invisibility would be to gather light from behind the craft and re-project that light in front of the craft, so that a viewer below sees the sky behind the craft instead of the craft itself. Here's what I mean (click graph to enlarge):
I could also see this being CG. Honestly there isn't much you can't do with computer graphics these days. The only way to come close to disproving this theory would be to analyze the original footage.
Video: Circular UFO Over Yokohama, Japan