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Tranquility Base

Astronaut Buzz Aldrin inspects equipment at Tranquility Base during Apollo 11's July 20, 1969, mission. The Passive Seismic Experiment Package sits in the foreground, and the Laser Ranging Retro-Reflector (LR-3) is in back. The instruments were designed to perform long-term lunar studies autonomously, long after astronauts left, and the LR-3 still returns data to Earth.

Photograph courtesy NASA