Neither theory nor observation support claims that lunar cycles can be used to forecast the weather

Ken Ring of Titirangi is New Zealand’s best known proponent of the idea that the Moon is an accurate weather forecasting tool. He publicly scoffs at official forecasters and climate scientists for ignoring the lunar effect, and the news media love him.

In 1999 he self-published a book expounding his theory (Predicting the Weather by the Moon). He willingly addresses community groups. He has his own website,, where he sells forecasts and peddles his theories, and he publishes an annual Almanac of daily weather forecasts for the coming year for 57 New Zealand towns. His theory can be summarised as follows: It is well known that the Moon’s gravity causes tides in Earth’s oceans and these can be predicted with great accuracy. There is some evidence of comparable tides in Earth’s atmosphere. Like the ocean tidal bulges, the atmospheric tidal bulges occur at points in the atmosphere roughly in line with the Moon, and like the ocean bulges, they sweep around the Earth daily (really Earth sweeps under them) due to Earth’s axial rotation. These atmospheric tides cause predictable changes in the weather due to the gas laws. Therefore the Moon’s position can be used to predict the weather.

The theory claims that monthly perigee (Moon closest to Earth) and fortnightly syzygy (Moon, Earth and Sun aligned at full and new Moon) cause atmospheric tide maxima sufficient to cause predictable bad weather at these times, in the same way that they cause the well-known weekly spring neap component of the ocean tides.

To anyone with the average hazy understanding of astronomical processes this would sound like very convincing science. But it is not as it seems. On scrutiny Ken Ring’s understanding of gravity and tidal force is poor, as is his understanding of astronomy and atmospheric science. On scrutiny his weather forecasts are no more successful than orthodox ones. It is obvious his book has not even been proofread let alone assessed by experts in astronomy and atmospheric science. It is riddled with typographical errors, careless mistakes, confusing sentences, muddled astronomical explanations and outright contradictions. Like its New Age stablemates it is a misleading mixture of correct and garbled science, folklore, astrology, misrepresentations of other authors, and hints of trickery and bluff. His attempts to match Moon events with weather events are amateurish with no analysis of statistical significance (this would not be possible with his crude data anyway).

According to Ring, “The weather is nothing more than the Moon pulling the atmosphere around.” What is wrong with this theory?

Firstly, the physical forces invoked could not have the supposed effects — they are so weak that they would be completely overridden by other more powerful forces. Secondly, the claimed correlations between weather events and Moon positions are spurious.

As any good weather textbook will detail, the behaviour of the atmosphere, both on large and small scales, is governed by the laws of thermodynamics driven by the Sun’s heat, which is vastly more energetic than gravity. There are also significant influences from Earth itself — its shape, axial rotation, the Coriolis effect, the orientation of its rotation axis to the Sun, its oceans and land masses, its ability to absorb and reflect heat, the composition and structure of its atmosphere, its own gravity (which exerts about 10,000 times more force on the atmosphere than the Moon’s gravity), and an array of chaotic factors associated with these influences, all of which combine to make weather prediction an inexact science at the best of times. The effect of the Moon’s gravity on Earth’s atmosphere, although it exists, comes a very distant and feeble last in the list of forces associated with the weather.

The tides are weak

The feebleness of tidal forces can be seen from the magnitude of the ocean tides. The tidal force from lunar gravity raises Earth’s oceans only about half a metre. (This is the calculated magnitude in mid-ocean due to the Moon only — the Sun adds a small fraction at syzygy. The tides we notice at sea coasts vary worldwide from 0.1m to 18m in bays, estuaries and coastlines due to the “slosh” effect around land masses). A half metre tidal bulge in Earth’s oceans is a minuscule amount in terms of Earth’s diameter (12,000,000 metres) and in terms of the depth of the oceans (about 4000 metres mean depth). A parallel tidal bulge in Earth’s atmosphere would not be detectable due to the mobile and less dense nature of gases. The mass of Earth’s atmosphere is about 300 times less than that of its oceans.

As Newton taught us, gravity is a function of mass and distance. The mutual gravitational force of attraction between two masses is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. This relationship dictates extremely weak forces in the case of small masses or great distances. Tidal forces are even weaker because they are a function of the difference between the gravitational force at the centre and that at a distance from the centre of the body being tidally influenced. These forces can be calculated by well-understood formulae and agree with measurements.

It is true, as Ken Ring tells us, that the Moon’s distance from Earth at perigee is significantly closer than at apogee — about one eighth closer. It is also true that the perigee tidal force of the Moon on Earth is about 50 per cent stronger than that at apogee. However, this translates to a tidal bulge in the ocean of 0.45 metres at apogee and 0.67 metres at perigee. This is a minuscule variation in terms of Earth’s size. A comparable variation in atmospheric tide would not be detectable and could not possibly contribute to the weather because it would be overwhelmed by the much more energetic thermodynamic processes.

The detection of atmospheric tides is problematic. Unlike ocean tides they could not be observed easily as a height variation because of the diffuse and mobile nature of gases. The upper boundary of the troposphere (the bottom layer of the atmosphere where the weather happens, and where 85% of its mass is located) cannot be defined more accurately than to the nearest kilometre. Its height is usually given in the range of 12-15 km at the equator and it is several kilometres lower at the poles. Its height varies, due to thermodynamic forces, by an amount far greater than any tidal bulge in the atmosphere due to lunar gravity — likely to be only a few centimetres.

These facts alone make detection of atmospheric tides problematic. The scanty evidence that exists comes indirectly by extrapolation from measurement of factors other than height. They have been identified as the cause of small barometric pressure variations observed as daily cycles above the equator. One study (Hutchings and Gellen, 1988) analysed about 30 years of daily sea-level atmospheric pressure readings from 16 stations on Pacific Islands in the tropical latitudes north of New Zealand. The authors determined the magnitude of the twice daily lunar tide component of sea-level atmospheric pressure at a maximum of about 0.1 hPa. This is much too small to affect the weather — it would be overwhelmed by the typical 20 hPa pressure variations associated with weather systems. There is also evidence that these observed barometric tides are partly caused by forcing of the sea-level atmosphere by the ocean tides.

Ring’s arguments are always directed at making the theory fit the known weather patterns. But any theory that atmospheric tides cause the weather must explain the absence of any regular weather pattern cycling twice daily in step with the tides (two tides a day, as with the oceans, from two tidal bulges on opposite sides of Earth). Ring’s version of the theory relies mostly on the long period tide cycles caused by the orbital motion of bodies, ignoring the twice daily cycles due to Earth’s axial rotation. The orbital period tides, such as the lunar syzygy quadrature spring neap tides and the perigee apogee tides, are only small components of the daily tides and their maxima are located at different latitudes on Earth. Occasionally Ring paradoxically refers to the daily tides with statements like, “If the Moon is in the sky there is less likelihood of rain.”

Supporting Evidence

By way of supporting the existence of atmospheric tides Ring lists in his bibliography a few journal articles on the subject but he doesn’t discuss them. Harry Alcock of the Waikato, the author of an earlier book expounding the theory (The Lunar Effect, 1989), described an experiment he conducted to test for the existence of atmospheric tides. Using a filtered photographic exposure meter aimed at the Sun he recorded the readings on cloudless days. He also recorded the Sun angle and Moon phase for each reading. He seems to have expected high atmospheric tides to allow less solar radiation through the atmosphere. He didn’t give any of the data, but simply declared, “The brightness readings under similar conditions, but different Moon phases, varied by an amount which suggested the atmospheric tide could alter by as much as 25 per cent.”

The naivety of this exercise will be obvious to anyone with a nodding acquaintance with scientific method. But Ken Ring swallowed it whole, recounting the experiment in his book and announcing the 25 per cent atmospheric tide as if it were established fact.

Long term Cycles

Ken Ring claims that weather patterns repeat over long term Moon cycles enabling you to predict the weather many years ahead for a specified location to the day. To support this claim he presents a table of eight serious droughts in Britain between 1853 and 1976 which purports to show that they fall into pairs separated by the length of the Metonic cycle — 19 years — or multiples thereof, give or take a year or two. But the pairs have been selected nonchronologically. When you put the eight drought years into chronological order none of them are separated by 19 years. The separations vary randomly from three years to 46 years. Furthermore, two of the pairs are repeated on the table, feigning seven pairs instead of five. Three of the drought years are used in more than one pairing, and two of the pairs are achieved by selecting conjoining drought years from the same drought (some of the droughts lasted up to two years).

To support his claim that the lunar perigee brings disasters Ring gives a table listing 11 disasters which occurred between 1931 and 1999. Two of them are earthquakes, one is a volcanic lahar, and the rest are weather related. Eight of them occurred in New Zealand and three elsewhere. Part of Ring’s theory is that earthquakes are also triggered by Lunar gravity maxima.

The table employs a cunning device. To increase the hit rate the definition of a hit is made as broad as possible. Five of the disasters are said to have occurred “in the same week” as perigee. The date of the disaster is deemed eligible for coincidence with perigee if it occurred within four of five days. This, of course, is approaching half way to apogee (seven days) when the lunar tidal force is on its way to its minimum. The table also has several errors and significant omissions. Three of the events are tropical cyclones that reached New Zealand, but he doesn’t attempt to determine when they formed, which is the crucial fact needed to validate his theory. On my count there are only five out of the 11 disasters on Ring’s table with convincing perigee coincidences (within a day). You could expect such a result by chance given that lunar perigee happens once a month.

Other Lists

He has more comprehensive lists on his website giving the date of every perigee in the previous year with a list of world disasters that happened around each. He notes that some disasters happen around apogee, but that doesn’t faze him. He simply invents a mechanism to make it fit, waffling on about potential energy being stronger than kinetic energy at apogee because the orbital speed is slower, and appealing to astrological talk about the Moon “giving its energy” to the Earth.

A recent study on earthquakes (J Vidal et al, 1998) analysed 13,000 earthquakes over 25 years from 1969 to 1994 along a section of the San Andreas fault. It found that when lunar tidal forces “favour” earthquakes the rate of quakes is only, at most, 2% higher — a statistically insignificant correlation with no predictive value.

Isobaric Maps

An intriguing feature of the annual Almanac is the isobaric maps drawn for every day for a year ahead. Ring implies that he generates his maps “using algorithms derived from past Moon cycles.” This sounds very impressive, but he doesn’t reveal the algorithms. I’ve compared his maps with Met Service maps over several months and never found more than superficial similarities. Some are glaring mismatches. Occasionally there is a mildly convincing chance hit.

He employs an engaging trick with his maps. He publishes two maps for each day, deliberately drawn very differently (using “lunar orbital calculations” of course), and invites you to select the one that matches the reality best. Now wait a minute. Aren’t these maps supposed to be a prediction? Or is this a matching exercise after the event?

Ring obligingly provides hints in his Almanac for doing your own forecasting. Some are akin to hints for fortune telling — couched in terms so general that virtually all possibilities are covered. Some don’t follow the principles of his own theory. For example, he says, “When perigee or apogee is close to new or full Moon, then a dry weather period can be expected (less than 36 hours between). When perigee or apogee is more than two days apart from the nearest new or full Moon then a wet period may be expected.” This contradicts his main argument that perigee and full and new Moon are the lunar positions strongly linked with rain.

The Bottom Line

Are Ken Ring’s weather predictions accurate? You don’t have to look hard to find evidence that they are not as impressive as he wants the world to think. Curiously, he has deemed it prudent to admit this in the disclaimer he attaches to his work: “The forecasts in this work are the result of best-of-ability endeavour. They represent the opinions of author and associates and no claim of 100% accuracy is made.” This rather dampens his claims about the superior forecasting capabilities of his theory. He also insists that we allow a three to four day latitude when interpreting his predictions. This nicely covers most of the possibilities, given New Zealand’s well known average three day high-low cycle, but negates his claim to be a reliable consultant for choosing a day to make hay or have a wedding.

I have found many cases where his predictions failed. For example, from January to July 2004 he predicted dry weather almost everywhere around the dates of six major rain events including the Manawatu floods in February. In the same period he also predicted widespread rain events which didn’t eventuate in two prolonged dry spells. I also compared his monthly rainfall estimates with actual rainfall and found that in only 18 of 78 cases did his estimate come anywhere near the actual rainfall.

It is hard to escape the impression that Ken Ring achieves his claimed 80 per cent forecasting success by a combination of luck and educated guesses based on known weather patterns. Nothing in his writings constitutes evidence that Moon positions are a useful weather forecasting tool, or that they are related to weather at all.

This article is condensed from two articles first published in the Auckland Astronomical Society Journal, October and November 2004, and published here by permission of the society. The full versions can be read at the society’s website,, in the Journal section.
Bill Keir is an amateur astronomer of Hokianga who has published many articles on astronomy.

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