Apollo 11 Laser Ranging Retro-Reflector full-size model

Apollo 11 Laser Ranging Retro-Reflector full-size model.

This is a replica of the first retroreflector left on the surface of the Moon during the Apollo 11 mission. Retroreflectors provide extremely accurate data on the distances between a celestial body and the Earth. They are made up of a small array of mirrors. Scientists on Earth aimed lasers at them and calculated the time it took for the beams to return to Earth. This allowed scientists to calculate the exact distances between the Earth and the Moon. They could also measure the Moon’s orbit and shape and observe how it was changed by the gravitational pull from Earth.

So far, six retroreflectors have been left on the Moon. Three have been left by NASA since the Apollo missions, two left by the Soviet Union as part of their Luna missions and one left by the Indian Space Organisation during their Chandrayaan programme.