On Apollo 11 en route to the Moon, I observed a light out the window that appeared to be moving alongside us. There were many explanations of what that could be, other than another spacecraft from another country or another world -- it was either the rocket we had separated from, or the 4 panels that moved away when we extracted the lander from the rocket and we were nose to nose with the two spacecraft. So in the close vicinity, moving away, were 4 panels. And I feel absolutely convinced that we were looking at the sun reflected off of one of these panels. Which one? I don't know. So technically, the definition could be "unidentified."