Photo: Measuring the distance of the moon from Earth is one way of testing Einstein's theory of relativity (Image: Dan Long)From New Scientist:
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 (1015) 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.
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