For centuries, humans have blamed the moon for our moods, accidents, and even natural disasters.
But according to a new study in the journal, the moon also affects something else -- our sleep.
In the paper, scientists from the University of Washington and Yale University in the United States and the National University of Quermes in Argentina noted that the human sleep cycle fluctuates during the 29.5-day lunar cycle: in the days before the full moon, people fall asleep later and sleep for shorter periods of time.
Using wrist monitors, the team followed 98 people living in three communities in Argentina's Formosa province.
Two of the communities are rural and one is urban.They then analyzed sleep monitoring data from 464 college students in the Seattle area.
The researchers looked at changes in sleep start times and sleep duration in rural and urban Settings, and found that their sleep cycles fluctuated.
The prevalence of this pattern may indicate that the moon has a significant regulatory effect on sleep.
Our natural circadian rhythm is somehow synchronized with, or linked to, the phases of the lunar cycle.
Even in cities with high levels of light pollution, this effect may be present.
The study confirmed that the night before the full moon, the participants fell asleep the latest and slept the least.
This is because the first quarter moon gets brighter with the arrival of the full moon, usually rising in the late afternoon or evening, with more natural light after dusk.
Although the second half of the waxing and waning phases also shine clearly, the moon rises very late.
Studies have also shown that light can interfere with sleep.
People in urban areas went to bed later and slept less than people in rural areas without electricity.
Whether the moon affects our sleep has long been a matter of debate among scientists. Some studies have hinted at lunar influence, but have been contradicted by others.
The new study showed clear patterns, in part because the team used wrist monitors to collect sleep data rather than other methods reported by users.
In addition, the researchers tracked different moon cycles, helping to filter out disturbances in the data, such as individual differences in sleep patterns and the presence or absence of lights.
"We hypothesize that sleep patterns are an innate adaptation, that the cyclical changes in the moon allowed our ancestors to take advantage of this natural light source."
