The July 11, 2009 issue of New Scientist ran a series of stories of why the moon still matters to astronomy, in celebration of the thirtieth anniversary of the Apollo 11 landing. One of them, by Stuart Clark, described how reflectors left on the lunar surface are helping test Einstein's theory gravity. Laser pulses bounced off these reflectors allow researchers to measure the distance between the earth and the moon to a precision of a few millimetres.
At such accuracy one has to factor in the effect of solar radiation pressure "which pushes the moon's entire orbit from its calculated path by about 4 millimetres."
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