Yogis love the moon, and we are not alone.

History is replete with rituals and ceremonies, dating thousands of years, celebrating her and her mystery. Myths, poems, and science fiction have all been inspired by her path across the heavens.

Walk into a yoga class on a full or new moon, and you are likely to hear that the moon is responsible for all sorts of mental states and physical ailments. She bears a heavy burden!

While we do not know the full extent of the relationship between the earth and moon, the most common explanation is: because the human body is comprised mostly of water, and the moon has an effect on the tides, then a new or full moon must have an effect on the human body and mind.

Is there a scientific basis for this claim, or are we merely falling prey to the illusory mind by dressing up faith-based ideas as fact?

The Moon is Always “Full”

The moon is technically always “full,” in that it does not disappear on the day of a new moon nor grow larger on the day of a full moon. It does not grow in size early in the evening when close to the horizon, only to shrink as it reaches its high point in the sky.

The distance of the moon from the earth is relatively constant. The moon does not follow a perfect circle around the earth, and the earth does not follow a perfect circle around the sun, but rather both have elliptical orbits. At its furthest point (called apogee), the moon is 252,088 miles away from the earth; at its closest (called perigee), it is 225,622 miles. The difference of 26,466 miles is not significant in terms of gravitational pull, though it makes a visible difference in terms of how big the moon looks to us on earth, especially when full. Both full and new moons happen on the apogee and perigee, meaning there is no relationship between the moon’s distance from the earth and whether the moon is “new” or “full.”

The earth spins around its own axis once every approximately 24 hours, providing a unit of time we call a day. The moon orbits the earth once every approximately 28 days, providing a unit of time measurement we call a month. The earth orbits the sun approximately once every 365.25 days, providing a unit of time we call a year. Because the earth spins around its own axis, both the sun and moon appear to circle the earth once every 24 hours.

The moon is in synchronous rotation with the earth, meaning the same side of the moon faces the earth most of the time. Since the earth orbits the sun, and the moon orbits the earth, the moon’s position in relation to the earth and sun changes. Sometimes the moon is between the earth and the sun; at other times the earth is between the sun and moon.

The following sounds counterintuitive: when the moon is between the earth and the sun, the moon appears dark to us. This is because the sun’s light is hitting the far side of the moon, leaving the side facing us in the dark, and we cannot see it from our vantage point. When the earth is between the sun and moon, we can see the moon because the light hits the side facing earth.

The Tides

Many people think that the moon causes the tides. This is only partly true – high and low tides are caused primarily by the earth’s rotation. Because the earth spins around its own axis once every 24 hours, the moon makes a complete circle around the earth: from a given point on earth, it appears closer to us for half the day, and for the other half it is hidden on the other side of the earth (what we call day and night).

The earth is comprised of land and water. Land is overwhelmingly static except for very slow movements of plate tectonics, which, when abrupt, is an earthquake. The oceans are a different story, however. The water in the oceans is vast, and is not contained, moving freely. In essence, it sloshes around the globe, like water sloshes around a five gallon tub in motion.

Compare this to a river, stream or lake. A lake has defined banks, and its water does not slosh around like the ocean. These bodies of water do not have an appreciable high or low tide as does the ocean.

As the earth spins, the moon exerts gravitational force on the water closest to it: the moon pulls the sloshing water towards it, creating a bulge, which we call high tide. On the other side of the earth, where the moon is furthest from the earth’s surface, the opposite is also a high tide: the water sloshes away from the earth, towards space, creating a bulge. Low tide appears in-between the bulges of water: since the water is pulled in opposite directions, it results in a low point in the middle. And since the earth is spinning around its own axis, with the moon staying relatively stationary, the bulge is constantly moving.

When the moon, sun, and earth are directly in line, an extra high tide can occur. This happens twice per month, and corresponds to the full and new moons, depending on the order of the celestial bodies.

If these relationships sound confusing, it’s because they are!

Four Moon Events Per Day

The claim is that because the moon exerts gravitational pull on water, it must affect the human body as well, as the body is composed of 60% water (depending on age). As a result, the theory goes, we need to practice yoga differently on moon days because of the moon’s influence.

There are scientific holes in this contention, however. First, water in the human body is intercellular. That means it is contained in cells and forms the building blocks of other substances like blood, plasma, and skin. Water does not exist in the body as pure water (H₂O) and there is no reservoir of water of the body, like a small lake or tank.

Compare this to a lake versus the oceans. The moon has no noticeable effect on the lake because it contains too little free flowing water to slosh around, unlike the oceans, which are so large that water sloshes and bulges, either because it is closer or farther from the moon.

We can use the bathtub for an experiment. Fill the bathtub with water, mark the line, and see if there is any difference based on the low and high tide. Absent evaporation, there will be no effect. The water in the human body is too small a volume, and does not exist as pure water, so it is reasonable to conclude that the moon does not have a noticeable effect on water in the body.

Which brings us to the larger point: there are generally four ‘moon events’ during any 24 hour period: two high tides, and two low tides. If the moon was to have an effect on the human body, it would happen in conjunction with the four moon events, because that is when the moon’s position changes compared to our static point.

Since yogis generally reserve their talks of the moon’s influence on our physical and mental bodies to the new and full moon, shouldn’t we actually be discussing the four moon events per day? This of course is not practical, and we would never end up practicing if we had to modify it according to all of the moon’s effects on the tides.

There is likewise little if any talk about the moon’s effect on the body on the day before or the day after a moon day, even though the relative distance of the earth to the moon has changed little, and the change in gravitational pull is miniscule. And what happens when the full moon occurs at 11:40 pm? Should one count that as the next day, or as the same day?

Many studies have been done by physical and social scientists trying to find a causal relationship between the human body and the moon. The consensus is that there is no proven correlation. This does not prove there is not an effect, just that one has yet to be found.

“Bad Man Coming”

In the Ashtanga Yoga tradition as taught by the late Sri K. Pattabhi Jois, practitioners take the day off on a new and full moon. I attended a conference (Q&A session) in Mysore, India, during the summer of 2004. A practitioner asked him about moon days. The response in broken English was “bad man coming. No yoga, no going outside, no going to work. . . . Bad man coming!” Pattabhi Jois was a Brahman, and a Hindu, so it is possible that his celebration of the new and full moons is rooted in his religious beliefs and not in physiology. Moon days are also known to change in Mysore, and elsewhere, to accommodate weekends or other travel schedules, depending on the instructor.

I fully support basing an idea or a ritual on a religious or faith-based practice. But we should properly categorize it as such rather than create unsupported claims merely to satisfy our demand for scientific and concrete explanations.

Dan Pitkow is currently an entrepreneur in Santa Monica. His first company, Flipper, makes a simple remote control for seniors, and others seeking simplicity in their everyday life and is in the Top 10 on Amazon.com. He studied Classics and Ancient Greek at the University of New Hampshire, before the University of Pittsburgh Law School. Before ‘coming’ to yoga, he was a competitive athlete, winning a high school and collegiate national championship in rowing. He currenlty practices ashatanga, completing the second series, with Jorgen Christiansen, and Tim Miller and Rolf Naujokat. Other yoga influences are Vinnie Marino, Shiva Rhea, and anyone who is teaching a class at a convenient time and location, preferably close to the beach. After leaving law, he travelled through Asia, India, China, Australia, central Europe and Greece. An armchair student of Joseph Campbell, and other science/creation myths, he believes that cross cultural similarities far outweigh their differences.