OUTBREAK IN THE SUN

Taranaki Daily News, 28 April 1934, Page 1 (Supplement)

OUTBREAK IN THE SUN

SUNSPOTS AND .WEATHER

(By the

Rev. B. Dudley,

F.R.A.S.)

Considerable attention has been given by experts to the question of sunspots with the definite object of determining, if possible, what they really are, and by what physical circumstances they are governed. The most ancient and pel - haps the most fascinating explanation is that propounded by Alexander Wilson, of Glasgow, whose theories were amended by Sir W. Herschel. Professor Wilson took it for granted that the sun is enveloped within two atmospheres, the outer one being luminous and therefore fittingly called the photosphere, while the inner one is nonluminous. He further supposed the spots to be openings in these two atmospheric layers by which we are able actually to see the darker solid body of the sun itself. Since then, however, the generally accepted opinion of scientists is that the sun is not a solid sphere, so that the Wilson theory, however attractive, has fallen into disfavour. Professor Hale, a noted American astronomer, was the first to put forward the idea that sunspots were often vertical in nature, although this had been guessed before. He detected indications of a cyclonic action in these spots, as if they might be storm centres. His conclusions on the matter have been largely accepted in view of the evidence that has been collected as a result of careful and patient observation. As most readers will probably know, there is an eleven-year rise " and fall in the magnetic condition of the earth.. It is known that terrestrial magnetism conforms to the periodic cycle just referred to. The situation is as follows: On occasion (no. warning being given and astronomers being unable to predict exactly when) there will break out on the solar surface an exceptionally large spot. This crosses the sun's face, from east to west, taking about thirteen days to effect the transit.,. Disappearing round the western edge of the sun’s disc, it will continue in being, eventually coming into view once more on the eastern edge of the sun, repeating the transit and making another and perhaps yet another rotation about the sun as it turns upon its axis carrying the spot with it. It is easily recognised to be the same spot by its solar latitude and other, signs.

Similarly, on the earth there arc occasions when, without giving warning, the magnetic needle becomes violently agitated. A magnetic storm, lasting for several days perhaps, follows or synchronises with this disturbance on the part of the needle. The agitation dies down with, or consequent upon, a quietening on the part of the sun until there is another solar storm reflected in a corresponding magnetic disturbance here, the connection between the one and the other being sometimes immediate and sometimes slightly separated by an interval of time. Just as there are ways by which solar storms can be recognised again, so terrestrial storms are subject to recognition if repeated. This is well known, and need not be gone into here. The interval between two successive returns of a spot to the same place on the sun’s disc represents practically the period of the sun’s revolution on its axis, which corresponds with the interval between the successive returns of magnetic storms on the earth. This accordance has been observed and tested over and over again, so that there is no doubt of it. The inevitable conclusion is that either magnetic variations on the earth are expressly due to sunspots, or both are more or less simultaneous expressions of some common cosmic cause. Of these alternatives the second is the more likely one. Very certainly, then, a maximum of terrestrial agitation, and a minimum condition in the sun’s "storminess is associated with a minimum of magnetic disturbance on the earth. It is also, known that the periodic rise and fall, in the . intensity and frequency .of auroral phenomena cljsely follows the rise and fall in the sun’s magnetic activities. Auroral displays in this sense are in other words symptomatic." ’ A somewhat novel element was introduced into this interesting study when a few years ago Professor A. E. Douglas worked out a test in order to ascertain to what extent weather -changes had left an impression on trees of great longevity as covering a period of, hundreds or even thousands of years. He studied in dry climates the annual rings of trees to see if there had been any dependence of these on the annual rainfall, the pines and sequoias of Northern Arizona affording him the necessary data. Proceeding on the assumption that the tree-rings measured the growth and that the growth was dependent generally on the amount of moisture, he selected trees whose lifetime extended back beyond the period during which sunspots have been observed telescopically, and made the discovery that they had actually been influenced by the eleven-year cycle already mentioned. Now it so happens that there was, after the year 1660, a remarkably long dearth of sunspots which is known-,to all astronomers; and this dearth, the professor found, was represented in . the treerings in an unmistakable way. Only in a general sense, however, can it be said that the sun determines the weather upon earth. And predictions, such as the cable report of a few days ago alluded to, are scarcely likely to have come from experienced astronomers. The cable was in any case sensational, to say the least. All that can be soberly claimed is that, the sun has practically passed a minimum period, and that spottedness' will in all probability increase during the next few years, and there may be a corresponding disturbance in magnetic conditions here. Exactly what form this will take depends largely upon local conditions. In any case, the effect of this correspondence between solar and terrestrial magnetic changes is feebler than is sometimes represented to be the case. Self-elected forecasters in America, claiming a special knowledge of solar affairs, have tried to obtain a fee for what was alleged to be “valuable information,” calculated to enable farmers to estimate their prospects as based upon the relation between the sun and the weather in the near future. In connection with the present spot group there is to be seen under telescopic scrutiny a display of faculae, consisting of bright, elevated streams belonging to the solar surface, such as are often found in greater abundance in the neighbourhood of dark spots. They are believed by some authorities to be the tops of clouds of vapour rising from the tremendous red flames or “prominences” that leap up from the surface of the sun to an enormous height, often many thousands of miles. The faculae are the more brilliant parts of the sun, and when in the neighbourhood of a spot, as at present, it is not difficult even with a small telescope, to detect their diversified form, having quite distinct outlines, and either separate or uniting in various ways into ridges and network.