In the literature concerning the Earth-Sun relations much space is devoted to the study of the possible influence of solar activity on weather and climate (glaciations, floods, droughts, and the like) The objective has been to find a correlation between natural events on Earth and the sunspots number (1,2,3,4).

As we have known from the secular observations, solar activity displays periodic time patterns with periods of 27 days, of about 11 years, of about 22 years, of about 90 years, and possibly some even longer.

The 11-year period, which concerns us here, is a measure of changes in a variety of phenomena occurring within the solar atmosphere (spots, faculae, flares, prominences, radio or X-ray bursts). The Wolf numbers, determined from observations of sunspots, constitute the most frequently used index of solar activity (5). Construction of the telescope by Galileo was of major importance for the solar spot observations. With more and more frequent optical observations of the Sun dating from 1610 onwards, and especially from the last half of the 18th century up to the present, we have at our disposal a practically uninterrupted record of the sunspot number (6).

The time interval between succesive minima in the annual means of Wolf numbers defines a cycle. According to Waldmeier's numeration (6) the first cycle began from the minimum of solar activity in the year 1755 preceded by the zero cycle with maximum in 1750.3. Now we are in the 22nd cycle, in the vicinity of the maximum, which has been forecast to be in 1991.1 (7,8). The exact date will be known later, after the analysis of observations.

Historical records and tests of C show (9) that during the past millennia solar activity varied considerably. In the recent thousand years these changes were characterized by the Great Maximum (AD 900 - 1300) and by the Minima of: Spoerer (AD 1420 - 1530) and Maunder (AD 1645 - 1715) (10,11). During the Great Maximum solar activity was much stronger than that observed at present in cycles 20th and 21st (a greater number of flares produces a higher level of solar cosmic radiation, this - in turn - causes greater disturbances within the terrestrial magnetic field, and hence an increased influence on the biosphere), while the two minima mentioned were much lower and more prolonged than the minimum in 1986 between the 21st and 22nd cycle.

It is also worthwhile to notice some correlation between solar activity and climate. In the period of the Great Maximum the Earth's mean temperature was higher, by some tenths of a degree (12), than at present (the current rise in the annual mean temperature is generally ascribed to the increasing carbon dioxide pollution of the atmosphere). In that time there also were the great expeditions of vikings and their discovery of a new land - now called America. Towards the close of that period the invasions of Tatars into Poland and other European countries took place: I - 1241, II - 1259/60, III - 1287/88.

Thus, the enhanced solar activity affected, - as the case may be - the history of geographical discoveries, "prodding" conquests and great migrations of peoples. Along with the development of technology man became independent of the whims of weather. Has the influence of solar activity on history diminished in our days ?

Let us examine this problem - although a reliable statistical justification cannot be readily provided here.

"History likes to repeat" - goes the popular saying. If something should repeat itself - there arises the question of how often, and one is immediately tempted to look for a pattern of these recurrences. We have noted some historical events (from Encyklopaedia Britannica), and how they relate to sunspot maxima. We confine our attention to Europe and Poland since 1750.

Fig. 1

From the list above, subjective and incomplete as it is, curious correspondence is seen between historical events and moments of maxima of solar activity.

Concerning recent times, which we can remember directly, the activity of the cycle 19th was the greatest one (already in 1956 the mean Wolf numbers exceeded 140). Cycle 20 was characterized by a flat maximum, where for three years, 1968-1970, the Wolf number was about 100 (1968 students' riots in Europe, "The Prague spring", the events in March 1968 and December 1970 in Poland).

The maximum of the 21st cycle was also extended over several years (1979 - 1981). After 13th December 1981 (the imposition of martial law in Poland) solar activity rapidly fell off (13).

Presently we are approaching the maximum of the 22nd cycle, which had been originally predicted to fall in 1991.1 (14,15). Possibly this is going to be a very strong maximum, the strongest or second - - strongest of all sunspot cycles ever recorded (16).

This maximum has apparently already reflected itself in the events in the USSR and in the countries of Central Europe. The minimum between the 22nd and 23rd cycles is expected in 1998.5, and the maximum of the 23rd will be in 2002.5, according to data from Cracow radio observations of the Sun at 810 MHz, which were started in October 1st, 1957 (see Fig.1).

From the last months' solar observations and considerations (17) one can conclude that the maximum of 22nd cycle will occur sooner than predicted before....(18).

Let's pass now to statistical considerations. There are two distributions available for our purposes: F(t) - annual means of Wolf numbers, f(t) - discrete function (observational series), with a step of one year with values: 0 or 1, where 0 - no remarkable historical event on the records 1 - there is at least one event of importance. Number of events n = 1....N. After convolution of these functions:

F[t]*f[t]/N = Sum[F[tn],{n,1,N}]/N = R,

and we obtain the mean value of Wolf number from the interval of 250 years. In the example from Table 1, N = 22 and R = 115.25 - 39.

Subsequently, there was made 10,000 runs of independent generating of observational series, with 22 elements each, covering the period from 1749 up to 1990.

In this way, the random distribution of occurrences of the mean Wolf numbers was obtained, which after normalization to 22 events, is represented on the Fig. 3 as a dashed line; there is also presented, as a full line, our observational series from the Table 1. It can be seen that the historical events presented here cannot be generated in any accidental way. Thus it can be accepted that there exists a close connection between the solar activity and historical processes on the Earth. In conclusion of the lecture, let us remind the dates of the next minimum (1998.5) and maximum (2002.5) of solar activity.

Let us keep these dates in mind and see if the history repeats.

Literature

(1) Materials from IX Astronomical Session in Dabrowa Gornicza 1980.
(2) Walczewski J., 1984, Prospects in Bioelectronics, Ed. Zon & Wnuk, KUL, Lublin, p.67 (in Polish).
(3) Michalec A., 1986, Urania 4, 120 (in Polish).
(4) Hoyle F., and Wickramasinghe N.C., 1990, Nature 343, 304.
(5) Schove D.J., 1979, Solar Phys. 63, 423.
(6) Waldmeier M., 1961, Schluthess Co. Zurich.
(7) Waldmeier M., 1981, Solar Phys. 73, 207.
(8) Chystiakow V.F., 1983, Solnetschnye Dannye 1, 97 (in Russian).
(9) Eddy J., 1976, Science 192, 1189.
(10) Sakurai K., 1979, Astrophys. and Space Science 63, 369.
(11) "The Maunder Minimum", 1976, Sky and Telescope 56, 394.
(12) Hansen J.E., and Lacis A.A., 1990, Nature 346, 713.
(13) Vitinsky Yu., and Miletsky E.V., 1985, Solnetschnye Dannye 4, 86.
(14) Chystiakow V.F., 1982, Solnetschnye Dannye 4, 97 (in Russian).
(15) Whitehouse D.R., 1985, Astron. Astrophys. 145, 451.
(16) Taylor P.O., 1989, J. Br. Astron. Assoc. 99, 236.
(17) Kane R.P., 1989, Solar Phys. 122, 175.
(18) Michalec A., 1993, 23rd Cycle of Solar Activity in the Light of 34 Years of Cracow Observations of Solar Radio Emission. Inside the Stars, 1993, IAU Colloqium 137, ASP Conference Series, Vol.40, pp. 87-89, Eds. W.W.Weiss and A.Baglin, San Francisco.

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