Full Moon Lunacy

13th June 2014 was a Friday and it also happened to be a full moon day. Full moon is a time when the whole moon’s disk is illuminated. Few news articles where boldly claiming that people go crazy (lunatic; mad) on a full moon day. But none of them gave any scientific reasons for why this is the case. I wanted to find out if this is true.

Light and Gravity are two ways by which moon can reach us. We can eliminate light from the equation as moon does not have light on its own. It reflects sun’s light. How do I know? If this was not the case then there will be no lunar eclipse. The other possibility is gravity.

The law of universal gravitation says that every object attracts every other object with a force. In this case the two bodies are moon and me. The next question is how much force does moon exert on me?

In the 17th century Isaac Newton came up with the formula for calculating the gravitational force. The formula is given below.


Mass of the moon is 7.35 × 1022 kilograms. To keep things simple let us assume that my mass is 100 kilograms. Moon is at a distance of 384,400 kilometers from Earth. Converting it to meters we get 3.84 * 108 meters. Substituting the values in the formula we get

F = (6.67 * 10-11 N (meter/kg)2 * 7.35 × 1022 kg * 100 kg) / (3.84 * 108 meter)2
F = 0.0033 Newton

Is the force 0.0033 Newton high or low? In order to answer this question we need to compare it with something else. Let us imagine that I am sitting 1 millimeter (0.001 meter) away from a vacuum cleaner weighing 2 kilograms. Let us find out how much force the vacuum cleaner exerts on me.

F = (6.67 * 10-11 N (meter/kg)2 * 2 kg * 100 kg) / (0.001 meter)2
F = 0.01334 Newton

Vacuum cleaner exerts four times (0.01334 / 0.0033) more force than the moon. Does it mean that the vacuum cleaner will affect my brain? Of course not. The moon is too far away from us to exert any force on our brains. Hence there is no scientific evidence that full moon can affect our brains. Excerpt from Scientific American

Following Aristotle and Pliny the Elder, some contemporary authors, such as Miami psychiatrist Arnold Lieber, have conjectured that the full moon’s ­supposed effects on behavior arise from its influence on water. The human body, after all, is about 80 percent water, so perhaps the moon works its mischievous magic by somehow disrupting the alignment of water molecules in the nervous system.

But there are at least three reasons why this explanation doesn’t “hold water,” pardon the pun. First, the gravitational effects of the moon are far too minuscule to generate any meaningful effects on brain activity, let alone behavior. As the late astronomer George Abell of the University of California, Los Angeles, noted, a mosquito sitting on our arm exerts a more powerful gravitational pull on us than the moon does. Yet to the best of our knowledge, there have been no reports of a “mosquito lunacy effect.” Second, the moon’s gravitational force affects only open bodies of water, such as oceans and lakes, but not contained sources of water, such as the human brain. Third, the gravitational effect of the moon is just as potent during new moons—when the moon is invisible to us—as it is during full moons.

May be there is another dimension beyond logic in which full moon might influence human brain. But I have not done enough work required to have an opinion in that. Let me end the post with an excerpt from the book Innumeracy: Mathematical Illiteracy and Its Consequences

Astrology maintains that the gravitational attraction of the planets at the time of one’s birth somehow has an effect on one’s personality. This seems very difficult to swallow, for two reasons: (a) no physical or neurophysiological mechanism through which this gravitational (or other sort of) attraction is supposed to act is ever even hinted at, much less explained; and (b) the gravitational pull of the delivering obstetrician far outweighs that of the planet or planets involved. Remember that the gravitational force an object exerts on a body—say, a newborn baby—is proportional to the object’s mass but inversely proportional to the square of the distance of the object from the body—in this case, the baby. Does this mean that fat obstetricians deliver babies that have one set of personality characteristics, and skinny ones deliver babies that have quite different characteristics?