Old conjecture about
sunspot structure In the 19th century, after the periodicity of the sunspot cycle was well established, people started wondering about what produced sunspots. Some theories thought of these features on the Sun as being similar to terrestrial cyclones, as the artist's impression on the left shows.

The near coincidence between the revolutional period of Jupiter and the sunspot cycle period initially led to an investigation of planetary influences on the Sun. However, most of this was "epidemiology" (sunpox?) with little thought to physical mechanism.

For instance, Jupiter certainly does exert a gravitational force on the Sun. However, that direct gravitational force can obviously have absolutely no relation to the sunspot cycle, because this force is constant (to first order) over the 11 year period. Only the variation of the distance of Jupiter from the Sun (about 5%), due to the Jovian eccentricity, which is a second order effect, could possibly show any variation over the 11 year period.

And if we are physically realistic, only a tidal force could really be conceived of as being responsible for any action on the Sun that might produce an effect. Now the tidal force is the first derivative of the gravitational force. It is how the gravitational force varies over distance, and as such is proportional to the cube of the distance of the planets. This means that Venus exhibits as much tidal force on the Sun as does Jupiter.

The big problem with most of these studies however, is that neither the direct gravitational force nor the tidal force varies by any appreciable magnitude (the only variation is due to the eccentricity of the planet's orbits, as they become a little nearer to and then further from the Sun).

Of course, some will point out that the Sun accelerates around the barycentre of the solar system, but again the variation of this acceleration is a very minor effect.

However, the magnetic fields in the Sun have a much greater control on the motion of plasma comprising the Sun, that we can safely neglect all but the solar gravitational field itself [see tables below].


The following table shows both the ratio and and the absolute values of both gravitational and gravitational tidal forces on the Sun due to the planets.

The first column is the ratio of the gravitational force (per unit mass) that each planet exerts on the Sun, normalised to the Earth. The second column is the tidal gravitational force exerted by each planet on the Sun (again normalised to the Earth). This tidal force is the difference in gravitational force over a unit distance (one metre) per unit mass. This varies as the cube of the planetary distance, not the square as does the direct gravitational force. Note that Venus is basically as effective as Jupiter in raising tides on the Sun (because of the inverse cube law).

The next two columns are the same quantities with absolute values. This is necessary to show that the magnitude of the tidal force is much smaller than the direct gravitational attraction. The last column calculates the energy density of the gravitational field due to a planet at the Sun. Note that this is the direct gravitational field density, not the tidal gravitational energy density which is a lot smaller.

Planetary Gravitational Fields
Planet     M/r^2     M/r^3   Grav(N/kg)  Tidal(N/kg/m) GravEnDens(J/m^3)

Mercury    0.35     0.9137    6.27E-09     2.16E-19        2.35E-08
Venus      1.56     2.1535    2.76E-08     5.09E-19        4.55E-07
Earth      1.00     1.0000    1.77E-08     2.36E-19        1.87E-07
Mars       0.05     0.0305    8.23E-10     7.20E-21        4.04E-10
Jupiter   11.74     2.2556    2.08E-07     5.33E-19        2.58E-05
Saturn     1.04     0.1093    1.85E-08     2.58E-20        2.04E-07
Uranus     0.04     0.0021    7.05E-10     4.90E-22        2.97E-10
Neptune    0.02     0.0006    3.37E-10     1.49E-22        6.78E-11

We should compare the above gravitational energy density with the energy density of the magnetic fields that we observe in sunspots. Values for the latter are given in the table below. Typically fields observed in sunspots range from about 10 to 3500 Gauss.

Magnetic Fields
MagField(G)   MagEnDens(J/m^3)
     1        3.97E-03
    10        3.97E-01
   100        3.97E+01
  1000        3.97E+03

Thus even for the smallest sunspot, the magnetic field energy density is four orders of magnitude larger than the gravitational energy density due to the presence of Jupiter. And really it is only tidal forces that could possibly cause any effects, not the direct gravitational field, which is constant. In this case the magnetic field has such a gigantic controlling factor on behaviour of the solar material, that it is no wonder that most solar physicists are not even prepared to look at any planetary influence.


Smythe and Eddy in 1977 reconstructed the tidal forces due to the planets on the Sun during the Maunder Minimum (1645 - 1715) when the sunspot cycle appears to have virtually disappeared. They found that the tidal forces however, did not disappear, and were essentially the same as they are now. This is another piece of evidence that makes it difficult to believe that the planets do in fact have anything to do with causing the sunspot cycle.

The abstract of the Smythe and Eddy paper published in Nature is given below (the full details of the paper are listed in the references at the end of this note).


The Jupiter Effect In 1974 Dr John Gribbin, a scientific journalist, wrote a book in conjunction with Dr Stephen Plagemann titled "The Jupiter effect".

The thesis was basically that:
(1) planetary positions affect the sunspot cycle
(2) peak sunspot number means the ejection of large clouds of magnetic plasma into space
(3) when these magnetic plasma clouds hit the Earth they cause discontinuities in the Earth's rotation rate
(4) abrupt changes in the Earth's rotational motion can trigger earthquakes

The authors then pointed out that 1982 was a year when a significant planetary alignment would occur, and that this could set off the above chain of events. (The US Naval Observatory wrote an illustrated rebuttal, pointing out that this 'alignment' was nothing of the sort. In fact all that could be said was that the planets were in a single 90o quadrant)

The lifestyles of a significant number of people were changed because of this book. One group/sect in Perth, Western Australia, was urged to obtain firearms and food, and head for the hills before the appointed day, so that they would be able to come back down and rebuild Perth society after the cataclysmic event.

One workman at Learmonth Solar Observatory told of how he had sold a lot of his possessions the preceding week so he would be prepared.

It is of course a matter of history that nothing happened on the fateful (fateless?) day.

Unfortunately, in true astrological style, many people are very good at forgetting about reality, and still talk about planetary alignments and sunspots. Gribbin has never really apologised for the problems his book caused although he has stated that he regrets ever becoming involved with the idea.


The real test of a scientific theory is its ability to predict future events, and this is where the idea of any sort of planetary alignment relationship to the sunspot cycle falls totally flat.

Many theories have been advanced in trying to predict the sunspot cycle, and none has been totally successful. Some appear to work for a cycle or two, and then collapse in ignominy. We must still confess almost complete ignorance as to the timing and amplitude of the sunspot cycle.

Among the predictions which appear in current scientific journals are ones which use statistical properties of previous cycles, ones which attempt some form of time series extrapolation, ones which look at precursor activity such as magnetic fields, and newer ones that attempt to emulate the magnetohydrodynamic(MHD) behaviour of the solar plasma.

What is now virtually absent from scientific prediction are methods employing planetary alignments. And for one good reason. They do not have any predictive value!


Alter D, "A New Analysis of Sunspot Numbers", Monthly Weather Review (US Weather Bureau), 56, 399 (1928)

Bigg EK "Influence of the Planet Mercury on Sunspots", Astronomical Journal, 72, 463 (1967)

Blizzard JB "Long Range Solar Flare Prediction", NASA Contractor Report CR-61316, Astron Journal, 70, 677 (1965); Bull Am Phys Soc 13 (June 1968)

Brown EW "A Possible Explanation of the Sunspot Period", MNRAS, 60, 599 (1899-1900)

Clayton HH, "The Sunspot Period", Smithsonian Miscellaneous Collections, p98 (#2) March 1939

Clayton HH "Planets and Sunspots", Popular Astronomy, p49 (#9), November 1941

Ferris GA, J Brit Astronomical Association, 79, 385-388 (1969)

Glassby Frank, Planets, Sunspots and Earthquakes : Effects on the Sun, the Earth and its Inhabitants, 300 pages, Writers Club Press (2002)

Gleissberg W, "Probability Laws of Sunspot Variations", Astrophysical Journal, 96, 234 (1942)

Gleissberg W, "Note on the Epoch of the Next Sunspot Maximum", Astrophysical Journal, 100, 114 (1944)

Gleissberg W, "The Apparent Distribution of Preceding and Following Sunspots", Astrophysical Journal, 102, 133 (1945)

Gribbin J, "Planets, Sunspots and Earthquakes", The Observatory, 93, 121 (1973)

Gribbin John & Stephen Plagemann, The Jupiter Effect, MacMillan, London (1974)

Interservice Radio Propagation Laboratory, National Bureau of Standards, Washington DC, "The Prediction of Solar Activity as a Basis for the Prediction of Radio Propagation Phenomena", Reprint No 25, November 1945

Jose PD, "The Sun's Motion and Sunspots", Astronomical Journal, 70, 193 (1965)

Luby WA "On the Cause of the Sun's Spots", Astronomical Journal, August 1930

Luby WA "Planets and Sunspots", Popular Astronomy, p523, December 1940

Luby WA "The Cause of Sunspots", Popular Astronomy, p49, February 1945

Maunder ASD, "An Apparent Influence of the Earth on the Numbers and Areas of Sunspots in the Cycle 1889-1901", Mon Not Roy Astr Soc, 67, 451 (1907)

Mathews H, "Planets, Sunspots and Politics", The Observatory, 94, 13 (1974)

Nelson JH "Circuit Reliability, Frequency Utilization, and Forecasting in the High Frequency Communications Band" in The Effect of Disturbances of Solar Origin on Communications, ed GJ Gassman, MacMillan New York (1963), p293ff; RCA Review, p26 (March 1951); Transactions IRE CS-2, #1, p19 (1954)

Schuster A "The Influence of Planets on the Formation of Sunspots", Proc Roy Soc London, A85, 309 (1910-1911)

Sharp Geoff A, "Are Uranus and Neptune Responsible for Solar Grand Minima and Solar Cycle Modulation?", International Journal of Astronomy and Astrophysics, 3, 260-273 (2013)

Stetson, Harlan True, Sunspots in Action, Ronald Press Company, New York (1947)

Stewart J and Panofsky H, "The Mathematical Characteristics of Sunspot Variations ", Astrophysical Journal, 88, 385 (1938)

Stewart J and Eggleston F, "The Mathematical Characteristics of Sunspot Variations II", Astrophysical Journal, 91, 72 (1940)

Smythe Charles M & John A Eddy, "Planetary Tides During the Maunder Sunspot Minimum", Nature, 266, 434 (1977)

Takahashi K "On the Relation between the Solar Activity Cycle and the Solar Tidal Force Induced by the Planets", Solar Physics, 3, 598 (1968)

Wood KD "Sunspots and Planets", Nature, 240, 91 (1972); see also Nature, 240, 129 (1965)

Although the earliest paper listed here which links sunspots and planets is that of Brown (1900), the historical paper by Ferris in the Journal of the British Astronomical Association (1969) states that Rudolf Wolf and Richard Carrington pointed out the possible link in the mid-nineteenth century, so the idea has been around for at least 150 years.

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