Mirrors on the moon

Each clear night when the moon is high in the sky, a group of astronomers in New Mexico take aim at our celestial neighbour and blast it repeatedly with pulses of light from a powerful laser. They target suitcase-sized reflectors left on the lunar surface by the Apollo 11, 14 and 15 missions, as well as by two Russian landers.
Out of every 300 quadrillion photons that are sent to the moon, about five find their way back. The rest are lost to our atmosphere, or miss the lunar reflectors altogether.
From this small catch, the team can assess the movement of the moon to an accuracy of a millimetre or two - a measurement so precise that it has the potential to show up any cracks in Einstein's general theory of relativity. If that's what it does, this lunar laser-ranging experiment will become Apollo's greatest scientific legacy.

Full story by Stuart Clark on New Scientist



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