Also see the Apache Point Observatory Lunar Laser-ranging Operation (APOLLO)[0]: "APOLLO measures the round-trip travel time of laser pulses bounced off the lun

Also see the Apache Point Observatory Lunar Laser-ranging Operation (APOLLO)[0]: "APOLLO measures the round-trip travel time of laser pulses bounced off the lunar retroreflectors[1] to a precision of a few picoseconds, corresponding to about one millimeter of precision in range to the moon." [0]: https://tmurphy.physics.ucsd.edu/apollo/apollo.html https://tmurphy.physics.ucsd.edu/apollo/apollo.html [1]: https://tmurphy.physics.ucsd.edu/apollo/lrrr.html https://tmurphy.physics.ucsd.edu/apollo/lrrr.html