Description
Photo of the Lunar Ranging Retroreflector (one of the ALSEP instruments) set up on the surface, taken by Dave Scott facing the sun during the first day of EVA. The Lunar Ranging Retro Reflector (LRRR) reflects laser pulses back to the telescopes on Earth used to illuminate it. By measuring the two-way travel time between the telescope and the LRRR, experiments can determine the distance between the two to a few centimeters and address such issues as Einstein's Theory of General Relativity and the existence of a liquid lunar core.
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