Clay, IV sec. In 1851, Schwabe (Schwabe) in Dessau announced that changes in the number of sunspots occur periodically, determining the period as 10 years. This discovery by Schwabe received well-deserved recognition in 1857, when he was awarded the gold medal of the London Astronomical Society. The president said in his speech on this occasion: “For twelve years he [Schwabe] spent on satisfying his own interests, the next six years on satisfying the interests of humanity, and finally, the 3rd. The position angle of the solar axis and the appearance of the solar equator are marked. Red line indicates that spots rarely appear at the equator. Fig. 4. Wolf’s curve. Dessau without Schwabe directing his unchanging telescope at it, and this apparently happened on average about 300 days a year for centuries.” The fact that sunspots appear and disappear quite regularly is indeed very interesting in itself, but it also means something more, since it obviously indicates the presence of certain changes within the Sun, regular and periodic in nature, dependent on physical and mechanical conditions that are not yet fully understood. The systematization of observations of sunspots accumulated over two and a half centuries was undertaken by the Zurich astronomer R. Wolf (Rudolf Wolf, 1816–1893). By processing all the material left by observers, he was able to establish a more accurate period of solar activity. This period averaged eleven years. At the same time, Wolf determined the years of maximum and minimum sunspot numbers – maxima and minima of solar activity – for the entire previous observation period. The numbers obtained from processing the observations he called relative – r – and determined them for each day of observation using the formula r = k(10g + f), where g denotes the number of groups of spots and individual spots at a certain moment in time, f is the total number of spots counted in these groups and individually, and k is a coefficient depending on the observer and his telescope.
This formula is still used today, although it certainly does not allow for a perfectly accurate expression of the state of the solar surface. This state is also determined by a whole range of other grand formations, so or otherwise related to spots: the size, number, and nature of solar eruptions and prominences, flocculi, faculae, etc. The curve – these are the main cycles of solar activity, averaging eleven years, but with individual deviations from 11 years in one direction or another. These main cycles of solar activity stand out most clearly, and thanks to them, the course of the sunspot formation process acquires a wave-like character with a gradual alternation of maximum and minimum points. Choosing any of these cycles from the minimum point to the next minimum point, we get one wave – one full cycle of solar activity, equal, say, to 11 years. Examining the course of this cycle, we will notice that the rise to the maximum does not occur gradually, but in jumps. In other words, the curve from the minimum point rises to the maximum point and then falls back to the minimum point not smoothly, but experiencing numerous jumps. The size of these jumps increases as the sunspot formation process intensifies and reaches its highest values at the maximum. Thus, the wave-like curve of the sunspot formation process is covered with a large number of small waves with sharp peaks at the top and deep, sometimes equally sharp, troughs at the bottom. From examining the sunspot formation curve, it is clear that it only vaguely resembles a sine wave. In detail, this curve is similar to the daily temperature curve of a typhoid patient, resembling the teeth of a semi-circular saw. Here we observe sharp rises and falls, shifts, and interruptions. All these are small fluctuations from which one large one is composed – the 11-year cycle of solar activity. Examining these jumps-teeth, it is easy to see, however, that as the cycle moves from minimum to maximum, they gradually increase in number and height; this means that spots appear on the surface of the Sun more and more frequently, in greater numbers, and have a longer lifespan. Consequently, the amount of energy radiated by them also gradually increases in jumps as the cycle moves from minimum to maximum. These jumps in the appearance and disappearance of spots are apparently the culprits of many effects that develop on Earth depending on spot formation.
Based on changes in the intensity and number of sunspots, Schwabe, as we have seen, believed that the time interval between maxima is equal to 10 years. Lamont calculated the same value and obtained 10.43 years for it. Wolf considered the period of sunspot number fluctuations to be 11.111 years with an average variability of ±2.03 years. Ch. Young (Joung, 1834–1908) believed that the true cycle of spot formation fluctuates no more than 12–14 years. A. Wolfer considered that on average the period of spot formation is 11.124±0.030 years. S. Newcomb (S. Newcomb, 1835–1909) accepted it as 11.13 years. Finally, Michelson (A. Michelson, 1852–1931) inclined to recognize a period above 11.4, but H. Turner (H. Turner, 1861–1930) believed that now we can only speak of a period of 11.4 years. Schuster subjected the numerical material on spots over 150 years to harmonic analysis. According to his research, alongside the 11.125-year cycle, there is a series of secondary periods, the successive entry of which is the cause of various disturbances observed in the main period. These secondary periods have values of 4.38, 4.80, 8.36, and 13.50 years. Studying the question of the 11-year period during 1750–1900, Schuster found that in the first 75 years this period breaks down into two: 9.25 years and 13.75 years, and over the entire 75 years it equals 11.1 years. It is interesting to note that Turner processed Greenwich magnetic observations for the period from 1841 to 1904, finding that in addition to the main period associated with sunspots, there is also a secondary period of 9.26 years. Desiring to discover the same period in solar activity, Turner began reworking all of Wolf’s and Wolfer’s data starting from 1610. Not finding periods of 9.26 years, Turner, however, established the presence of another period of solar activity, namely 13 years. This period is distinguished by the property that, despite its low intensity, it is quite well expressed. Finally, in 1927, Oppenheim subjected Wolf’s numbers to a new analysis and found that the curve of their course is expressed by the following function: r = C + C2 cos [φ1 + λxm – cos (mφ1 – εm)], φ = 360°/Π, 25i, v = 360°/450. Thus, spot formation is a very complex phenomenon. Only on average is one period equal to 11 years. In reality, its duration sometimes reaches 17 years, and sometimes only 7. Also, a very significant phenomenon in the cyclical course of the number of sunspots must be recognized as the fact that the buildup to the maximum, the period of its duration, and its decline do not each time constitute something strictly definite, but gradually vary due to causes still unknown to us. Therefore, in determining and more so in predicting any specific point of the period, one must be extremely cautious. The turning points in solar activity, marking the points of highest rise and lowest fall, can only be determined after several months, and sometimes a year or more, by comparing with data on solar activity over a more or less long period. The forecast available to us so far regarding the determination of the 11-year cycle can only be given with an accuracy of 1–2 years, but even this can sometimes be very significant.
In addition to attempts to discover small cycles of solar activity, research has been conducted to determine whether there are large periods in solar activity. As early as 1746, when nothing was known about periods, Mairan pointed to the possible existence of large periods in solar activity. Later, the same idea was shared by Loomis. Wolf attempted to find such a period, determining it as 55.5 years. Young suggested that there is a fluctuation of 60 years, which is superimposed on the main oscillation of 11 years. A. Ganskiy determined them as 72 years. N. Lockyer found a 35-year period in solar activity, and Schuster calculated using the periodogram method cycles of a third of a century, equal to 33.375. Litznar also came to the establishment of a 33-year period in solar activity. Finally, Turner found it possible to conclude the existence of a long period of 266 years. According to this scientist, every 266 years there is a great maximum of solar activity. In 1889, Wolf, based on data from medieval Chinese chronicles about auroras, identified several dates that could be the dates of great maxima in solar activity. These were the years: 372, 840, 1078, 1337, and 1372. Based on the years 372 and 1372, during which, according to his assumption, there was particularly strong solar activity, Wolf calculated a series of large periods, namely 88.33 and 66.67 years. Then Wolf sequentially added these numbers to 372, thus obtaining a table of dates for great maxima of solar activity. However, the dates outlined by Wolf can now be disputed. But what are sunspots? Has their “great secret,” as Galileo said, been unraveled in our time? Perhaps not yet, but what we have learned about spots and their nature in recent years is enough to form an idea of the great significance of sunspots for the life of the Earth.
Many outstanding minds have grappled with unraveling the nature of sunspots. The first observers thought that spots were planets, the nearest satellites of the Sun passing near its surface. This erroneous idea was refuted by Galileo, who in turn believed that spots were clouds floating in the solar atmosphere. Derham believed that these clouds originated from eruptions of solar volcanoes. J. Lalande considered them to be the peaks of solar mountains protruding from the ocean of fire over the surface of an island glowing on the central solid core of the Sun. W. Herschel believed that spots were temporary openings in the clouds through which we can see the dark body. The material by which we can judge to some extent the epochs of solar activity are the chronicle records of auroras. The latter, as established, in certain latitudes occur mainly when the Sun is experiencing an epoch of maximum. Other data are large sunspots visible to the naked eye during maxima and noted by chroniclers (mainly the Chinese). This material was scattered across the annals and chronicles of various peoples. The systematization of this material belongs to the German scientist H. Fritz, who first in 1893 processed the chronicle data on auroras, sunspots visible to the naked eye, hailstorms, and harvests. Twenty-five years later, a similar work was carried out by D. O. Svjatsky in Russia. His work also took into account Russian chronicles.
In 1868, two theories began to compete: the theory of Abbot A. Secchi and the theory of E. Faye. The first based his theory on the hypothesis of solar eruptions. The second considered solar storms as the basis of spot formation, and the structure of spots themselves as vortex-like. This starting point retains its significance to this day. Faye’s theory is that due to the relative motion of adjacent parts of the photosphere, whirlpools form, which turn into cyclones and vortices similar to those that occur when a fast current encounters obstacles. Such vortices resemble funnels in which the body and floating air are drawn into the depths. Similarly, as Faye then assumed, terrestrial cyclones and tornadoes occur. They begin from above and descend into the atmosphere lower and lower until the top of the vortex reaches the Earth. Vortices of this kind, but only colossal ones, constitute, according to Faye, the essence of a sunspot. One of the objections to Faye’s theory was that if spots are vortices, they should exhibit vortex motion. Moreover, all spots north of the equator should rotate in the same direction, counterclockwise when viewed from Earth; spots in the southern hemisphere of the Sun should rotate in the opposite direction, similar to terrestrial cyclones. Studying this issue, astronomers noticed that only a small percentage of spots show traces of vortex motion, and often different members of one group of spots, even different parts of the same spot, rotate in opposite directions. At that time, these observations could only shake Faye’s theory, but meanwhile they are the best proof of the correctness of his principle about the vortex structure of spots. The vortex theory of spots was supported by electrical theories. Fierce advocates of the vortex theory of spots were Rayet and Helm. However, for its final recognition, clarity in some details was lacking. Only after the brilliant work of the American scientist G. Hale, published in 1908, did most astronomers return to the vortex theory. Finally, the following year, Hale was able to conclude based on numerous studies that sunspots “are apparently electrical vortices.” Hale’s brilliant works initiated a whole series of excellent studies on the nature of spots conducted at the Solar Observatory on Mount Wilson in California, as well as in other observatories studying the Sun. Hale’s theory found many ardent supporters among astronomers, especially since it received new and new confirmations every day.
Thus, sunspots should be regarded as vortices similar to sea tornadoes, with funnel-like expansions at the top. The movement of matter in such vortices occurs from bottom to top, forming an ascending vortex. The speed of matter movement reaches enormous values, and the gases carried in the vortex cool down due to their rapid expansion as they approach the top of the vortex. The tops of the vortices that have reached the surface, cooled gases move in spirals with rapidly increasing radii. What we see in the form of a spot is only the top, the end of the vortex, an echo of the grand processes occurring in regions inaccessible to our study. Undoubtedly, there is a cause that forces gases from the depths of the Sun to rise. There, in the lower layers of the solar sphere, a cosmic force is hidden that drives this complex and enormous tornado, bearing the modest name of a sunspot. The cause that causes the vortex movements of the photospheric matter has not yet been considered firmly established. In this direction, there are only more or less substantiated assumptions. Perhaps the nearest cause should be considered the strong heating of matter at depth? Then, becoming lighter, like air in a chimney, it rises upward. Along the way, due to the ascent, the gases cool and emerge on the surface colder, although initially they were strongly heated. This implies that in the lower layer, where the phenomenon originates, there must be a very high temperature. Indeed, while near the surface of the Sun the temperature does not exceed 6000°, in the central layers it reaches approximately 12,000,000°. According to the calculations of R. Emden, the central temperature of the Sun is 31,500,000°. H. Russell showed that most stars have a central temperature very close to 32,000,000°.
The cause of such heating in the lower layers of the Sun remains an unsolved mystery for now. This mystery becomes even more incomprehensible if we take into account that spots appear in certain parts of the solar surface and only in certain latitudes. Before this hurricane, our storms that uproot trees and houses are like gentle breezes. As early as 1892, Young, spectroscopically studying the radiation of sunspots, discovered a remarkable phenomenon, namely: many spectral lines of sunspots turned out to be double, whereas the spectrum of the rest of the solar surface remained single. This phenomenon, called the Zeeman effect, indicates the presence of magnetic fields in sunspots. Fig. 10. Red curve – prominences from 1910 to 1934. Dotted curve – sunspots for the same period (according to W. Brunner).
