By the Light of the Silvery Moon

Lunar influence determines high and low tides in the ocean, but can it also affect human beings? Maura Imbert considers the myth of moon-madnes

  • Photograph by Maura Imbert
  • Photograph by Maura Imbert

To me, the full moon is at its ultimate, beautiful best when it rises over a Caribbean beach on a clear, star-filled night. Magnificent, a glittering orb tinged with gold, it appears over the horizon and then, rising higher and higher, it shines down on silver-tipped waves and shadowed sands. Is it any wonder that Earth’s satellite was worshipped as a goddess by the first inhabitants of the West Indies, or that its motions were accurately recorded by many ancient cultures?

When you walk along the shore and watch the waters pile up under the Moon at high tide, you are watching one of the forces at the heart of motion in the universe — the force of gravity. As the Moon revolves around the Earth, its gravitational pull also causes tidal effects in the Earth’s atmosphere which influence weather patterns, tidal effects in the Earth’s crust, and even in the Earth’s core. At the same time, the Earth’s gravitational pull on the Moon causes tidal effects in the lunar crust — there are no high ocean tides on the Moon, since our satellite has neither an atmosphere nor oceans, in spite of the fact that the dark areas on its surface were thought to be seas by early astronomers.

The Moon’s tidal effects are strongest at both full moon and new moon, when the Sun and the Moon are roughly in line and pulling together, and the orbital positions of both the Earth and the Moon at these lunar phases can have dramatic effects on the ocean’s high tides. This was brought home to me some years ago when I had an anxious call from a contractor who was building a wall around a new beach house in Mayaro. To my astonishment, he demanded a reason for the fact that the sea was lapping against his new wall when normally even the high tide mark was some metres down the beach. Sadly for this contractor, he failed to take into account that exceptionally high tides, like the one he was experiencing, can occur if the Moon, in its elliptical orbit, is at its closest point to the Earth (at perigee) at either new or full moon. Such perigean tides only occur two or three times a year. The tides can be even higher if the Earth happens to be at its closest point in orbit to the Sun (at perihelion) when the Moon is at perigee, as the combined gravitational attraction of both the Moon and the Sun on the oceans is then at its greatest.  While this is a relatively rare phenomenon, it was the reason for the contractor’s distress that day in Mayaro!

The Moon’s recognised tidal effect on the oceans inevitably leads to speculation about other tidal effects, such as those on plants and animals, including man. There’s a saying that even an archbishop (why an archbishop?) is 80 percent water, so it is reasonable to suppose that the Moon could affect human beings, but some scientists point out that the water in human and other living tissues is “bound water” and would not experience tidal effects. Others directly relate the composition of living human tissue to the composition of the Earth, and differentiate the water in the human body into freely running (the water in blood) and “bound water” (the water in cells), maintaining that all the water in the body is related and subject to gravitational influences. To these researchers, the full moon can precipitate violence, traffic accidents and psychotic behaviour, and they cite statistics in support of their claims — claims hotly refuted by those who firmly deny such influences and cite their statistics. “Biological tides” form an area of scientific research which, like the ocean, appears to be in a state of constant agitation!

Adherents of the hypothesis of biological tides believe that plant sap is also subject to gravitational influences, and this belief may explain the prevailing Caribbean opinion that bamboo should only be cut when the Moon is below the horizon, as otherwise the cut stems would be too full of gravitationally elevated, insect-attracting sap. A lunar enthusiast, with whom I corresponded recently, also mentioned the possibility that many insects mate and lay eggs at full moon, and that the bamboo would be more likely to be infested if cut in moonlight at this lunar phase.

Biological tides are also considered responsible for the effect of the full moon on marine life forms, and it is recorded that shellfish renew their shells and carry out sexual activity according to Moon phase, and that certain fish have a colour sensitivity on their skins which responds to the full moon. Lunar tidal effects are also observed in oysters, which open their valves to feed when the Moon is on the meridian, and harvesting shrimpers take advantage of the shrimp’s rising to the surface at full moon. The Moon is also reputed to affect mammals, and many predators are more active at full moon, including wolves — a fact well-known to trappers.

A somewhat related research project, recently carried out in the United Kingdom, also records the effects of the full moon. Over 1,000 cases of hospital treatment of dog bites were researched, and there was a direct correlation between the time when the bites occurred and full moon phase! Strangely, a similar research project carried out in Australia showed no correlation whatsoever. This suggests that different forces may be dominant in northern and southern hemispheres — a suggestion supported by recent data from Earth-monitoring satellites that investigate atmospheric conditions in both hemispheres and continue to find surprising and hitherto unknown anomalies.

Before lunar effects are dismissed as mere folklore, in spite of compelling evidence to the contrary, one has to recognise that many factors, some still unknown, can influence a particular investigation. Until these factors are included, the jury is still out in the case of the many effects of our satellite, the Moon.


In our September/October Science Beat, Dr Pathmanathan Umaharan, who is working on plant genetics and the transformation of plant shape and colour, was wrongly named as Dr Uma Rahaman. Caribbean Beat would like to sincerely apologise to Dr Umaharan, who is a distinguished Senior Lecturer in Genetics at the Faculty of Science and Agriculture at the University of the West Indies, St Augustine, Trinidad. He was recently honoured as one of the four “best teachers at the University of the West Indies” at the Guardian Life/UWI Premium Teaching Awards.

Funding provided by the 11th EDF Regional Private Sector Development Programme Direct Support Grants Programme.
The views expressed on this website are those of the the authors and do not reflect those of the Direct Support Grants Programme.