What are moon phases?
The moon's mystery stems from its nightly transformation. Some nights the floating sphere is plump and shiny, and after a few weeks it becomes a faint crescent. While the moon appears to physically change each night, this is just an illusion caused by a complex astronomical dance.
The moon does not emit its own light, but is illuminated by the sun. Depending on the position of the sun, moon, and earth in relation to each other, varying amounts of reflected sunlight are visible from the earth. Our changing perspective of Earth creates the Moon's changing shape.
Starting as a complete disk (full moon), the moon appears to gradually shrink each night until it is completely invisible (new moon). At that point, the moon will slowly fill in until the disk is complete again. It takes the moon 29.5 days to complete this process.
The Moon's cyclical changes are divided into eight phases, each of which indicates the precise shape created by visible reflected sunlight, and whether that shape is increasing (crementing) or decreasing (decrementing). The eight phases are: new moon, first quarter moon, first quarter moon, first quarter moon, full moon, waning moon, first quarter moon, and last quarter moon. Each phase is associated with a different position of the moon, earth, and sun.
It should also be noted that the moon appears in a different part of the sky each night as it orbits the Earth once a month. This repositioning affects the timing of moonrise and moonset, delaying moonrise by approximately 50 minutes3 each day. A full moon only occurs when it is opposite the Earth and the Sun, so it rises in the evening and sets in the morning. When the moon reaches the new moon phase, it aligns with the sun and the two rise and set together.
Does the moon phase affect sleep?
The lunar influence on biological rhythms is well documented in nature. Changes in the diameter of trees, how crabs reproduce, spawning events on the Great Barrier Reef and the nocturnal activity of owl monkeys may all be affected by the lunar cycle. Research on the possibility of moon phases affecting humans is less clear—most studies are small-scale and the results are somewhat inconsistent.
Nonetheless, compelling evidence suggests that lunar cycles may affect sleep, with the full moon phase being the most disruptive.
A sleep study analysis used several indicators to find that the full moon is associated with worse sleep. During this moon phase, participants took 5 minutes longer to fall asleep, slept 20 minutes less, took longer to reach REM sleep, experienced 30% less deep sleep, and experienced decreased sleep quality.
Another study found that total sleep time decreased by 25 minutes during a full moon, while arousal and arousal increased. However, participants in this study took longer to reach REM during the new moon, which contradicts previous research. A third analysis examined data from 319 people who underwent a one-night sleep study. People observed during the full moon were less efficient at sleeping, had less deep sleep, and had a delay in reaching REM sleep.
In the most extensive study on the subject, researchers analyzed sleep patterns in three indigenous Argentinian communities and 464 American college students living in a major city. Regardless of the location and amount of artificial light, all groups needed more time to fall asleep and spent less time sleeping overall in the week before the full moon.
Why does the moon affect sleep?
Moonlight
Many people believe that full moons cause sleep disruption due to the amount of sunlight reflected back to Earth. The body's internal 24-hour clock is calibrated by the rise and fall of hormone levels in response to light perception. Therefore, light level is one of the most important factors affecting the onset and quality of sleep.
However, there is concern that the brightness of the moon is the primary mechanism of sleep disruption. The brightness of moonlight is only 7% of the intensity of sunlight, which is a relatively low intensity. People are often exposed to much more artificial light at night than is reflected by the moon. Additionally, studies on sleep disruption during the full moon have typically been conducted on cloudy nights or in closed, windowless environments.
Electromagnetism
Another hypothesis that is becoming increasingly popular is the moon's ability to cause electromagnetic fluctuations on Earth. Earth's electromagnetic field has a long tail or "magnetotail" formed by the solar wind. As the Moon orbits the Earth each month, it passes through the magnetotail during the full moon phase and becomes negatively charged. The Moon's magnetic charge can then influence the Earth's electromagnetic field through a complex feedback process.
Research now suggests that humans may be sensitive to low-level geomagnetic changes. Other geomagnetic events that produce geomagnetic fluctuations comparable to lunar effects (such as geomagnetic storms and the Aurora Borealis/Australia [Northern Lights/Aurora Australis]) are associated with a range of health effects, including headaches, changes in blood pressure and blood flow, heart rate variability, and even heart attack. While the exact biological basis of these changes is unknown, research points to several mechanisms involving the body's hormone levels, DNA breakage, and inflammation.
Gravity
The idea that the moon's gravity affects human health is based on the fact that most of the human body is water, and the moon's gravity has a significant impact on ocean tides. Critics of the theory point out that the moon's gravitational pull on humans is very small. Researchers estimate that the impact of lunar tides on humans is less than one millionth the size of an atom.
The moon's gravitational pull is also roughly equal during the full moon and new moon. Therefore, any changes in sleep that occur during a single lunar phase are unlikely to be caused solely by changes in gravity.
Does the moon phase affect children’s sleep
The impact of lunar phases on pediatric sleep patterns has not been well studied, and the limited data available are ambiguous. A study of nearly 6,000 children in 1,312 countries found that sleep duration was only 1% shorter during the full moon phase compared to the new moon phase. Another analysis 14 actually found that children sleep more during the full moon. Interestingly, researchers attribute the extra sleep to increased daytime activity, but how the moon affects children's activity levels is unclear.
A German study 15 looked for relationships between lunar cycles, sleep and physical activity in 1,400 teenagers. After three years of data collection, there was no discernible correlation between moon phases and sleep or activity levels.
The moon, sleep and mental health
The potential impact of the moon on sleep may be particularly important for people with mental illness, as many of these conditions have a bidirectional relationship with sleep. In fact, the word "lunacy" comes from "Luna", the Roman goddess of the moon.
Recent research highlights a possible relationship between moon phases and symptoms of bipolar disorder. In one study, patients' mood cycles often synchronized 17 throughout the 37-year lunar cycle. A follow-up study19 also demonstrated a link between lunar phases and bipolar mood cycles, although its exact basis is unclear.
The impact of lunar cycles on other mental health disorders, such as anxiety and depression, has been a source of speculation. However, multiple studies 20 studying 21 assessing the link between lunar phases, anxiety, and depression have found no evidence of this.
Does the moon have a gendered effect on sleep?
The influence of the moon on female fertility has been controversial since ancient times. 22. Many people believe that the phases of the moon control the menstrual cycle and affect fertility. If this is true, then one could envision a mechanism by which the moon affects sleep by acting on female hormones. It has been established 23 that sleep problems can be caused by hormonal changes during menstruation, pregnancy, and menopause.
Modern research investigating the relationship between moon phases, female reproductive patterns and sleep is conflicting. One study spanning 15 years found that participants' menstrual cycles were intermittently synchronized 24 with the phases of the moon, with periods occurring before either the full moon or the new moon.
Women's data was analyzed using a period tracking smartphone app, looking for correlations 25 between falling asleep, menstruation and moon phases. There is no correlation between menstruation and moon phases. However, those who started when the moon was half full reported better sleep. Women whose menstrual cycles begin when the moon is less than half full often have poor sleep.
There are few studies comparing the effects of the moon phase on sleep in men and women. However, some studies have noteworthy findings. In another study comparing moon phases and sleep patterns, female participants experienced decreased sleep duration, decreased stage 4 sleep, and decreased REM sleep around the full moon. Male participants experienced increased REM during the full moon. Other studies have noted slightly different sleep metrics for men and women during the full moon, but the results have been inconsistent and often conflicting.
Tips for better sleep
While there is some compelling research suggesting that moon phases may affect sleep, at this point, the research is only suggestive. There's a lot we don't understand about this topic. Fortunately, there are some evidence-based strategies that can help you get a good night's sleep tonight, regardless of celestial influences.
Sleep hygiene is one of the most approachable and helpful ways to get a good night's sleep. This includes adjusting your bedroom environment and practicing certain behaviors to help you fall asleep successfully. Simple things like making sure your bedroom is dark, limiting caffeine, avoiding blue light and maintaining a sleep schedule can go a long way.
