The full moon this weekend will provide North America with a lunar eclipse and will likely lead some to believe that maternity wards will become busier. A new report shows they won't — baby booms are just one of the myths that have sprung up around lunar phases.
The eclipse will be visible across North America, as the moon passes through the shadow of the Earth, turning blood red in the process.
The effect is due to the alignment of the Earth, moon and sun and follows the recent total solar eclipse in the North Atlantic. No special equipment is needed to view the lunar eclipse; in fact, the naked eye is the best way to capture it.
Full moons are often blamed for a variety of human activities. A person whose behaviour is strange might be called a lunatic (from "luna", Latin for moon); wolves seem to howl by it; while some people apparently turn into wolves or vampires under full moonlight.
Then, there is the common urban myth that more babies are born during a full moon. But statistical studies have shown that this is not the case.
Yet, the myth persists among well educated people. The author of the new study says this is a form of "confirmation bias," where we interpret information in a way that confirms our beliefs and ignore that which contradicts them. This keeps the myth alive, even though it goes against scientific evidence.
It is also dangerous.
Most of us are guilty of confirmation bias in some form or another. For instance, I'm obsessed with red lights in traffic. I never get green ones, no matter what speed I drive.
Of course, when I did keep track of traffic lights on a short trip across the city, the count came out to roughly 50- 50, with a slight red bias. But my sample size was relatively small. If I had kept track of the lights for a month, in other words, the bias would likely disappear.
But I haven't done that experiment, which is exactly the point. We don't bother to do the research. Plus, when we believe something to be true, we don't want to let go of that belief, especially when a lot of other people believe it as well.
Regarding the baby birth myth, the gravity of the moon, which does cause tides, has an insignificant effect on the human body. Gravitational pull depends on the mass and distance of the two objects. Our oceans are very massive, so they feel the tidal pull, but the human body is not.
The moon is also very far away. So, in fact, the gravity from the mass of the hospital building exerts a greater gravitational pull on a pregnant woman than that of the moon.
On top of that, the tidal pull of the moon is strongest not just during the full moon - when the Earth, moon and sun are aligned - but it is also stronger during the new moon, when the moon is on the same side as the sun. But there are no stats to show more babies born then, either.
The danger of confirmation bias is when false beliefs lead to harmful effects. The recent outbreak of measles in the U.S. is believed to be based on the misconception that vaccinations are harmful. Beliefs about the alleged health or sexual benefits of rhino horn are driving those animals to extinction. The science of evolutionary biology is threatened by beliefs that the Earth is only 6,000 years old and Darwin was wrong about the evolution of life. And then there is the belief that human activity is not warming the atmosphere, which is stalling efforts to clean up our greenhouse gas emissions act.
Myths and legends are an important part of culture, a colourful way to teach lessons in morality. But when direct scientific evidence proves the contrary, we have to make a choice between what we believe in and what evidence tells us is the truth.