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Event

Lunar Laser Ranging experiment

A large, box-like structure with a reflective surface emitting beams of light stands on a lunar landscape, symbolizing the Lunar Laser Ranging experiment.

A continuous measurement programme begun in 1969, when Apollo 11 astronauts placed an array of corner-cube retroreflectors on the Sea of Tranquility. Observatories at Apache Point, Grasse and elsewhere fire short laser pulses at the panels and time the round trip. After more than fifty years the technique has pinned the Earth-Moon distance to millimetre precision and confirmed that the Moon is drifting away at 3.8 centimetres a year.

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