What was the shadow I saw pass across the moon?

To block out the moon it would have to have been a huge chunk of rock a long way off, or a smaller piece much closer to the Earth. But in either case we would have known about it because of the obvious risk to satellites and to the Earth itself. Also, it probably would have gone on to burn up in the atmosphere, producing a bright light which we would have seen. But it seems very unlikely that what you saw was actually in space. As it appeared so large, it could well have been an aeroplane, or possibly a helium weather balloon...or perhaps a stealth aeroplane or even a UFO !?