July 17, 2009 -- You've heard them time and again. There's a man in the moon. It's made of cheese, elicits madness and inspires love.
Since the beginning of human history, civilizations around the world have been bewitched by Earth's nearest neighbor, making up myths linking the moon to everything from the human psyche to the rhythms of nature.
Even now that science has shown us that it's no more mysterious than anything else we can reach out and touch, surveys indicate that people can't shake superstition. Nurses blame a full moon for more chaos and incoming patients. Police have linked full moons to aggressive behavior.
On this 40th anniversary of the moon landing, let's consider where these beliefs and urban legends come from.
Experts point out that much of the intrigue comes from the lunar phases.
For people looking up the night sky centuries ago, the irregularity of the moon, especially compared with the constancy of the sun, was mystifying.
'What Is the Moon For?'
"The moon is regular in its cycle, but it's not so absolutely regular that it didn't take time for people to figure it out," said Erika Brady, a professor in the department of folk studies and anthropology at Western Kentucky University. "It seems to link psychologically with the nine months of the human gestation period and the woman's menstrual cycle, and that linkage has always fascinated people."
The moon's purpose was equally enigmatic.
"The sun provides heat, light, life," said Ben Radford, managing editor of The Skeptical Inquirer magazine, who has written about moon superstitions. "But what's the moon for? Because the moon doesn't have a clear, intuitive purpose, people will imagine the things that the moon does and the influences it has on us."
For the Mayans, the moon goddess brought floods and powerful storms down upon Earth through her serpentine assistants. For the Aztecs, the moon was the decapitated head of a malevolent, matricidal goddess.
Moon Inspires Fear and Awe
Even etymology gives us insight into our distrust of the moon -- the words lunacy, lunatic and loony all have their origins in the word 'lunar.' The belief that werewolves morph into their canine incarnations when the moon is full reveals this suspicion too.
But not all cultures beheld the moon as a purely fearsome force. In some civilizations -- such as ancient India, Rome and Greece -- the moon goddess was portrayed foremost as the sister of the sun god, with less attention paid to her character. In Western astrology, the moon is supposed to embody a person's realm of feeling and govern the unconscious.
To be fair, there is a hint of logic to the myths linking the moon and human behavior. Earth, much like the human body, is composed mostly of water. If the moon's gravitational pull can affect ocean tides, so the reasoning goes, couldn't it also affect a person's body?
But the science doesn't bear this out.
"Published [research] does not confirm that there is a change in the amount of violence, reported crimes or aggressive behavior during a full moon," Eric Chudler told ABC News. Chudler, a research associate professor in bioengineering at the University of Washington in Seattle, has studied more than 100 research papers on the purported effects of the full moon on human affairs.
Nurses, Police Officers Link Full Moon to Chaos
Still, people persist in believing otherwise. Studies have found that police officers and hospital workers are among the strongest believers in the notion that more crime and trauma occur on nights when the moon is full.
Dr. David Mandell of the Children's Hospital in Pittsburgh and some colleagues studied existing data on health-care myths and did a 2005 study of area nurses. He said he found that 69 percent of surgical nurses in his study believed that a full moon led to more chaos and incoming patients that night.
"It is unbelievable how many nurses in southwest Pennsylvania believed in the superstitions," he told ABC News. But he said that it's simply part of the culture of medicine.
Moon Myths Cluster Around the Unpredictable
"In any high-stress, fast-paced field like medicine, superstitions run rampant when you feel a loss of control. This is especially true of emergency environments [because] you never know what will walk in. You need some way to explain the unpredictability of your environment," he said. "It passes on from senior to junior people in hospitals -- like old times telling it to new residents coming in."
Western Kentucky's Brady said that phenomenon isn't confined to just hospitals.
"You'll find that these beliefs that cluster around the moon, they are also relevant to parts of human behavior that are unpredictable," she said. "It's a way of imposing a categorical order on something that otherwise feels frighteningly out of control."
Some people consult the lunar calendar when deciding when to have surgery, she said. Each part of the zodiac corresponds with a part of the body (for example, legs and ankles are linked to Aquarius, sexual organs to Scorpio). And, as the moon moves through the different signs, the superstitious caution against medical intervention on that body part or region.
For farmers whose livelihoods depend on the health of their crops, planting by the phases of the moon is still common in some rural areas, she said.
Lunar Superstitions Provide Comfort
The Farmers' Almanac, for example, advises planting crops that are valuable because of the parts that grow above ground (such as corn and wheat) while the moon is waxing, so that the moon pulls the plant out of the ground while it grows bigger.
Conversely, it advises planting root crops (such as turnips and yams) while the moon is waning so that the diminishing moon helps the vegetables grow deep into the ground.
She's also seen scientifically-trained physicians refuse to castrate livestock during certain phases of the moon because they think they'll bleed out. They've never seen documentation or evidence supporting that notion, she said, but cite anecdotes from their uncles or older family members.
Risks run high in matters of health and agriculture, and moon myths ease the fear.
"There's a comfort factor that accompanies authority that extends back in time," she said. "If your feeling is that you are exerting a level of control and authority, that can reduce an element of anxiety."
ABC News' Liam Berkowitz, Chris Francescani and Brittany Bacon contributed to this report.