Robert Roy Britt
Editorial Director
LiveScience.com robert Roy Britt
editorial Director
livescience.com – Fri Sep 25, 5:41 pm ET
The moon holds a mystical place in the history of human culture, so it's no wonder that many myths - from werewolves(A person believed to have been transformed into a wolf ) to induced lunacy to epileptic seizures - have built up regarding its supposed effects on us.
"It must be a full moon," is a phrase heard whenever crazy things happen and is said by researchers to be muttered commonly by late-night cops, psychiatry staff and emergency room personnel.
It's been a long time since the Big Cheese revealed any new secrets as important as this week's announcement that traces of water exist all across its surface. Coincidentally, a study this week found zero connection between the full moon and surgery outcomes.
In fact a host of studies over the years have aimed at teasing out any statistical connection between the moon - particularly the full moon - and human biology or behavior. The majority of sound studies find no connection, while some have proved inconclusive, and many that purported to reveal connections turned out to involve flawed methods or have never been reproduced.
Reliable studies comparing the lunar phases to births, heart attacks, deaths, suicides, violence, psychiatric hospital admissions and epileptic seizures, among other things, have over and over again found little or no connection.
One possible indirect link: Before modern lighting, the light of a full moon have kept people up at night, leading to sleep deprivation that could have caused other psychological issues, according to one hypothesis that awaits data support.
Below, I'll review several studies - the good, the bad and the in between - but first some basic physics:
The moon, tides and you
The human body is about 75 percent water, and so people often ask whether tides are at work inside us.
The moon and the sun combine to create tides in Earth's oceans (in fact the gravitational effect is so strong that our planet's crust is stretched daily by these same tidal effects).
But tides are large-scale events. They occur because of the difference in gravitational effect on one side of an object (like Earth) compared to the other. Here's how they work (full explanation of tides):
The ocean on the side of Earth facing the moon gets pulled toward the moon more than does the center of the planet. This creates a high tide. On the other side of the Earth, another high tide occurs, because the center of Earth is being pulled toward the moon more than is the ocean on the far side. The result essentially pulls the planet away from the ocean (a negative force that effectively lifts the ocean away from the planet).
However, there's no measurable difference in the moon's gravitational effect to one side of your body vs. the other. Even in a large lake, tides are extremely minor. On the Great Lakes, for example, tides never exceed 2 inches, according to the National Oceanic and Atmospheric Administration (NOAA), which adds, "These minor variations are masked by the greater fluctuations in lake levels produced by wind and barometric pressure changes. Consequently, the Great Lakes are considered to be essentially non-tidal."
That's not to say tides don't exist at smaller scales.
The effect of gravity diminishes with distance, but never goes away. So in theory everything in the universe is tugging on everything else. But: "Researchers have calculated that a mother holding her baby exerts 12 million times the tide-raising force on the child than the moon does, simply by virtue of being closer," according to Straightdope.com, a Web site that applies logic and reason to myths and urban legends.
Consider also that tides in Earth's oceans happen twice every day as Earth spins on its axis every 24 hours, bringing the moon constantly up and down in the sky. If the moon's tugging affected the human body, one might presume we'd be off balance at least twice a day (and maybe we are).
Studies of full moon effects
Here are some of the reputable studies in peer-reviewed journals that have failed to find connections:
EPILEPSY: A study in the journal Epilepsy & Behavior in 2004 found no connection between epileptic seizures and the full moon, even though some patients believe their seizures to be trigged by the full moon. The researchers noted that epileptic seizures were once blamed on witchcraft and possession by demons, contributing to a longstanding human propensity to find mythical rather than medical explanations.
PSYCHIATRIC VISITS: A 2005 study by Mayo Clinic researchers, reported in the journal Psychiatric Services, looked at how many patients checked into a psychiatric emergency department between 6 p.m. and 6 a.m. over several years. They found no statistical difference in the number of visits on the three nights surrounding full moons vs. other nights.
EMERGENCY ROOM VISITS: Researchers examined 150,999 records of emergency room visits to a suburban hospital. Their study, reported in American Journal of Emergency Medicine in 1996, found no difference at full moon vs. other nights.
SURGERY OUTCOMES: Do doctors and nurses mess up more during the full moon? Not according to a study in the October 2009 issue of the journal Anesthesiology. In fact, researchers found the risks are the same no matter what day of the week or time of the month you schedule your coronary artery bypass graft surgery.
Not all studies dismiss lunar influence.
PET INJURIES: In studying 11,940 cases at the Colorado State University Veterinary Medical Center, researchers found the risk of emergency room visits to be 23 percent higher for cats and 28 percent higher for dogs on days surrounding full moons. It could be people tend to take pets out more during the full moon, raising the odds of an injury, or perhaps something else is at work - the study did not determine a cause.
MENSTRUATION: This is one of those topics on which you will find much speculation (some of it firm and convincing-sounding) and little evidence. The idea is that the moon is full every month and women menstruate monthly. Here's the thing: Women's menstrual cycles actually vary in length and timing - in some cases greatly - with the average being about every 28 days, while the lunar cycle is quite set at 29.5 days. Still, there is one study (of just 312 women), by Winnifred B. Cutler in 1980, published in the American Journal of Obstetrics & Gynecology, that claims a connection. Cutler found 40 percent of participants had the onset of menstruation within two weeks of the full moon (which means 60 percent didn't). If anyone can tell me how this oft-cited study proves anything, I'm all ears. Also, one should be skeptical that in the intervening 29 years, nobody seems to have produced a study supporting Cutler's claim.
ANIMALS GONE WILD: A pair of conflicting studies in the British Medical Journal in 2001 leaves room for further research. In one of the studies, animal bites were found to have sent twice as many British people to the emergency room during full moons compared with other days. But in the other study, in Australia, dogs were found to bite people with similar frequency on any night.
SLEEP DEPRIVATION: In the Journal of Affective Disorders in 1999, researchers suggested that before modern lighting, "the moon was a significant source of nocturnal illumination that affected [the] sleep-wake cycle, tending to cause sleep deprivation around the time of full moon." They speculated that "this partial sleep deprivation would have been sufficient to induce mania/hypomania in susceptible bipolar patients and seizures in patients with seizure disorders." Best I can discern, however, these oft-cited suggestions have never been tested or verified with any numbers or rigorous study of any kind.
Myths persist
If one presumes that modern lighting and mini-blinds have pretty much eliminated the one plausible source of human-related moon madness, why do so many myths persist?
Several researchers point out one likely answer: When strange things happen at full moon, people notice the "coincidental" big bright orb in the sky and wonder. When strange things happen during the rest of the month, well, they're just considered strange, and people don't tie them to celestial events.
"If police and doctors are expecting that full moon nights will be more hectic, they may interpret an ordinary night's traumas and crises as more extreme than usual," explains our Bad Science Columnist Benjamin Radford. "Our expectations influence our perceptions, and we look for evidence that confirms our beliefs."
And that leads to this final note, which is perhaps the biggest logical nail in the coffin of the moon madness myths:
The highest tides occur not just at full moon but also at new moon, when the moon is between Earth and the sun (and we cannot see the moon) and our planet feels the combined gravitational effect of these two objects. Yet nobody ever claims any funny stuff related to the new moon (except for the fact that there is more beach pollution at full and new moon ...).
In The Water Cooler, Imaginova's Editorial Director Robert Roy Britt looks at what people are talking about in the world of science and beyond. Find more in the archives and on Twitter.
LiveScience.com chronicles the daily advances and innovations made in science and technology. We take on the misconceptions that often pop up around scientific discoveries and deliver short, provocative explanations with a certain wit and style. Check out our science videos, Trivia & Quizzes and Top 10s. Join our community to debate hot-button issues like stem cells, climate change and evolution. You can also sign up for free newsletters, register for RSS feeds and get cool gadgets at the LiveScience Store.
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Top 10 Amazing Moon Facts
NASA's Lunar Reconnaissance Orbiter (LRO), slated for launch this week, will map the moon's surface from orbit with unprecedented detail, capable even of imaging the tracks that lunar rovers left behind.
Also heading moonward is the Lunar Crater Observation and Sensing Satellite (LCROSS), which will slam into the Shackleton Crater on the south pole of the moon in a few months and kick up material that could have been in shadow for 2 billion years. Another probe will slam into the moon a few minutes later at a different location.
It's all an effort to learn more about what the moon is made of, whether there is water ice in the crater, and therefore where to send U.S. astronauts in a planned return by 2020.
The Big Whack
The moon formed as a result of a collision known as the Giant Impact or the Big Whack, scientists figure. It went like this: A giant Mars-sized object hit Earth 4.6 billion years ago shortly after the birth of the sun and the solar system. A cloud of vaporized rock was kicked up (a mix of Earth and the other object) and went into orbit around Earth. The cloud cooled and condensed into a ring of small, solid bodies, which then gathered together, forming the moon.
Earth Makes the Moon Rise
Each day, though not at the same time, the moon comes up in the East and goes down in the West -- much like the sun and other stars and for the same reason:
Earth rotates, on its axis, toward the East, pulling celestial objects into view and then forcing them to slip away. The moon also makes an orbital trip around Earth once every 29.5 days. In the sky, this gradual movement is eastward, though it's not perceptible during any given observing session. It is, however, why the moon rises later each day, by about 50 minutes on average.
That also explains why the moon sometimes rises in the evening and us up during the night, while at other times it's up only or mostly during the day.
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No 'Dark Side'
Contrary to what you might have heard, there is no "dark side" of the moon. There is, however, a "far side" that we can't see from Earth. Here's why:
Long ago, the Earth's gravitational effects slowed the moon's rotation about its axis. Once the moon's rotation slowed enough to match its orbital period (the time it takes the moon to go around Earth) the effect stabilized.
So the moon goes around the Earth once and spins on its axis once, all in the same amount of time, and it shows us just one face the whole time.
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Gravity is Much Less
The moon is about 27 percent the size of Earth and far less massive. Gravity on the moon is only about 1/6 of that on Earth. If you drop a rock on the moon, it falls more slowly (and astronauts can hope much higher). If you weigh 150 pounds on Earth, you'd weigh 25 pounds on the moon.
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Bigger and Smaller Full Moons
The moon's orbit around Earth is an oval, not a circle, so the distance between the center of Earth and the moon's center varies throughout each orbit. At perigee (PEHR uh jee), when the moon is closest to Earth, that distance is 225,740 miles (363,300 kilometers). At apogee (AP uh jee), the farthest position, the distance is 251,970 miles (405,500 kilometers).
When a full moon rises while it's at apogee, the disk we see can be 14 percent bigger and 30 percent brighter than other full moons.
The moon is not bigger when it rises compared to later at night, however; that's an illusion (one that causes a lot of argument over what causes it). You can test this yourself by holding something about the size of a pencil eraser at arms-length when the moon first rises and looks so huge, then repeat the test later in the evening when the moon is higher and looks smaller. Next to your eraser, it'll look comparatively the same in both tests.
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Pockmarked History
The craters on the moon reveal its violent history. Because there is almost no atmosphere and little activity inside the moon, the crater trace a record of impacts back billions of years (unlike Earth, which would have been just as violent back then, but the craters have all been weathered away or folded back into the planet).
By dating the moon's many craters, scientists figured out that the moon (and Earth) underwent a Late Heavy Bombardment around 4 billion years ago. The latest thinking on this pummeling is that life may have survived it, if biology had gotten a foothold that early.
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Not Round
The moon is not round (or spherical). Instead, it's shaped like an egg. If you go outside and look up at the moon, one of the small ends is pointing right at you. And the moon's center of mass is not at the geometric center of the satellite; it's about 1.2 miles (2 kilometers) off-center. Earth, likewise, bulges in its midsection.
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Caution! Moonquakes
Apollo astronauts used seismometers during their visits to the moon and discovered that the gray orb isn't a totally dead place, geologically speaking.
Small moonquakes, originating several miles (kilometers) below the surface, are thought to be caused by the gravitational pull of Earth. Sometimes tiny fractures appear at the surface, and gas escapes.
Scientists say they think the moon probably has a core that is hot and perhaps partially molten, as is Earth's core. But data from NASA's Lunar Prospector spacecraft showed in 1999 that the moon's core is small -- probably between 2 percent and 4 percent of its mass. This is tiny compared with Earth, in which the iron core makes up about 30 percent of the planet's mass.
One engineer thinks these moonquakes should be taken into account when future lunar bases are designed.
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Tugging on the Oceans
Tides on Earth are caused mostly by the moon (the sun has a smaller effect). Here's how it works:
The moon's gravity pulls on Earth's oceans. High tide aligns with the moon as Earth spins underneath. Another high tide occurs on the opposite side of the planet because gravity pulls Earth toward the moon more than it pulls the water.
At full moon and new moon, the sun, Earth and moon are lined up, producing higher than normal tides (called spring tides, for the way they spring up). When the moon is at first or last quarter, smaller neap tides form. The moon's 29.5-day orbit around Earth is not quite circular. When the moon is closest to Earth (called its perigee), spring tides are even higher, and they're called perigean spring tides.
All this tugging has another interesting effect: Some of Earth's rotational energy is stolen by the moon, causing our planet to slow down by about 1.5 milliseconds every century.
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Ciao, Luna!
As you read this, the moon is moving away from us. Each year, the moon steals some of Earth's rotational energy, and uses it to propel itself about 1.6 inches (4 centimeters) higher in its orbit.
Researchers say that when it formed about 4.6 billion years ago, the moon was about 14,000 miles (22,530 kilometers) from Earth. It's now more than 280,000 miles, or 450,000 kilometers away.
Meanwhile, Earth's rotation rate is slowing down -- our days are getting longer and longer. Eventually, our planet's tidal bulges will be assembled along an imaginary line running through the centers of both Earth and the moon, and our planetary rotational change will pretty much cease. Earth's day will be a month long. When this happens, billions of years from now, the terrestrial month will be longer -- about 40 of our current days -- because during all this time the moon will continue moving away. [Moon Mechanics: The Full Story]
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