‘As the LHC’s Pauline Gagnon describes at the Quantum Diaries, the changing force exerted by the Moon as it orbits—the same thing that drives the tides—creates subtle differences in the position of the hardware within the LHC. The differences are tiny for any individual piece of hardware, but they add up when it comes to something as big as the LHC, which has a circumference of nearly 27km. Plus, the LHC hardware is very, very sensitive to being out of alignment, given that it has to accurately direct bunches of protons that are moving at nearly the speed of light.
The net result is that the LHC’s operators sporadically have to tweak the beam’s alignments, leading to a temporary drop in the rate of collisions, seen as periodic dips in the plot above. According to Gagnon, the operators also have to make tweaks in response to everything from the level of water in nearby Lake Geneva to the passage of the French high-speed rail.’