In 2002, some folks thought they had found a new moon in the sky. What a disappointment when they figured out what it really was.
In September of 2002 an amateur astronomer spotted something going around the Earth that he couldn't identify. He thought maybe Earth had a second moon that had never been noticed before. The object was small enough to have escaped detection, but it wasn't a satellite, it wasn't an airplane, it wasn't the space shuttle.
But what it was is almost as interesting. Researchers at MIT used an infrared telescope owned by NASA and situated on top of a mountain in Hawaii to examine the potential moon carefully. Other researchers at the University of Arizona caught images of light bouncing off the object; by putting together their findings, these two groups were able to figure out what it was.
It was a piece of a rocket, still orbiting the Earth. In particular, the Saturn V rocket used in the Apollo 12 mission, launched in 1969. Our "new moon" was actually an "old spaceship"-launched over thirty years ago.