As a kid, I loved the skylight in my room for one huge, glowing reason: I could lie on the edge of my bed and fall asleep in the moonlight, all cozy in my PJs. I felt like the luckiest little girl in the world to be able to bask in the cool light of the moon.
But not everyone takes that view. Many people say a full moon keeps them awake or prevents them from achieving deeper sleep. A research paper in the journal Current Biology backs them up. In a small study of 33 people, researchers found that the phase of the moon does affect sleep.
For three and half days, the subjects of the study, ages 20 to 74, were ensconced in a lab, where their hormone levels and sleep patterns were tracked.
"We found that around full moon, electroencephalogram (EEG) delta activity during NREM sleep, an indicator of deep sleep, decreased by 30%, time to fall asleep increased by 5 min, and EEG-assessed total sleep duration was reduced by 20 min. These changes were associated with a decrease in subjective sleep quality and diminished endogenous melatonin levels," the study authors wrote.
It's not about brightness
Knowing that bright streetlights can keep people awake, we might guess that a full moon would have a similar effect. But the most interesting part of the study may be that sleep disturbances linked to the moon's phases seem to have nothing to do with the moon's light.
In fact, during the study, the moon's brightness wasn't a factor at all. The test subjects spent their time in a room without windows, and didn't even know that the data collected would have anything to do with the moon phases. (That way, personal perceptions or beliefs about the moon's influence on their sleep could be minimized.)
"We have evidence that the distance to the nearest full-moon phase significantly influences human sleep and evening melatonin levels when measured under strictly controlled laboratory conditions, where factors such as light and personal moon perception can be excluded," the authors wrote.
The pull of the moon
How does the body react to something that isn't even visible? One theory is that it's a holdover from our evolutionary past. We know that some species' circadian and reproductive cycles are tied to the moon, so the human brain might have some version of that trait, too.
"We don't know whether humans still have it and why," Christian Cajochen of the Psychiatric Hospital of the University of Basel in Switzerland, lead author of the study, told CNN.com.
This effect might vary between men and women, too, a study conducted in Surrey, England, found. In that study, 205 people were tracked as they slept (also in windowless rooms) over the lunar cycle. "Separate analyses for men and women indicated that in women total sleep time, Stage 4 sleep and REM sleep were reduced when sleep occurred close to full moon, whereas in men REM duration increased around full moon," the authors of that study wrote.
No study has looked at what effect age or other conditions might have on sleep quality as it's tied to the moon, so there's still a lot to learn. To understand this phenomena, scientists will need to collect more data from more people over a longer period of time.
In the meantime, if you want to do an unscientific exploration of your own sleep patterns, here are the remaining full moons of 2019:
Aug. 15: Sturgeon Moon
Sept. 14: Harvest Moon
Oct. 13: Hunter's Moon
Nov. 12: Beaver Moon
Dec. 12: Cold Moon
Editor's note: This story has been updated with new information since it was written in August 2017.