Researchers in Switzerland say they have found scientific evidence that the moon's lunar cycle can influence sleep.
A study of 33 volunteers found that just as some myths say, when the full moon is high it is harder to slumber and brain activity related to deep sleep dropped by 30%.
Scientists believe an internal clock that follows the cycles of the moon may be hardwired into our genes and it ticks away even on nights when the moon cannot be seen.
Dr Christian Cajochen, from the University of Basel, said: "The lunar cycle seems to influence human sleep, even when one does not 'see' the moon and is not aware of the actual moon phase."
The findings are published in the Current Biology journal.