In 2013 a Swiss lab reported that volunteers slept twenty minutes less and had thirty per cent less deep-sleep brain activity around the full moon — in a sealed room with no windows.

The design was the striking part: nobody knew the study was about the Moon, and the data had been collected years earlier for something else. It has not replicated cleanly. Larger studies find much smaller effects or none, and the journal itself later published a critique about unpublished null results. It remains the best evidence there is, and it is not strong.