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Given a scientific passage and an answer, generate a question for the given answer.

Passage: The Moon is easily seen from Earth. Early astronomers used telescopes to study and map its surface. The Moon has also seen a great number of satellites, rovers, and orbiters. After all, it is relatively easy to get spacecraft to the satellite. Also, before humans could be safely sent to the Moon, many studies and experiments had to be completed. Answer: moon
Output:
What celestial object has been visited by manned spacecraft and is easily seen from earth?