Lunar effect

The term lunar effect refers to correlations between specific stages of the roughly 29.5-day lunar cycle and behavior in humans or other living things. In some cases these rhythms may depend on external cues, such as a greater or smaller amount of moonlight due to the moon's phases. In other cases, for example the approximately-monthly cycle of menstruation, the correlation in timing may reflect no known lunar influence. Some purported effects cannot simply be explained by variation in light levels.