Chapter XV The Sun’s Journey through Space
Having gained some idea of the nature of the electrical hypothesis of solar disturbances and of the possible effect of other bodies upon the sun’s atmosphere, let us now compare the astronomical data with those of geology. Let us take up five chief points for which the geologist demands an explanation, and which any hypothesis must meet if it is to be permanently accepted. These are (1) the irregular intervals at which glacial periods occur; (2) the division of glacial periods into epochs separated sometimes by hundreds of thousands of years; (3) the length of glacial periods and epochs; (4) the occurrence of glacial stages and historic pulsations in the form of small climatic waves superposed upon the larger waves of glacial epochs; (5) the occurrence of climatic conditions much milder than those of today, not only in the middle portion of the great geological eras, but even in some of the recent inter-glacial epochs.
1. The irregular duration of the interval from one glacial epoch to another corresponds with the irregular distribution of the stars. If glaciation is indirectly due to stellar influences, the epochs might fall close together, or might be far apart. If the average interval were ten million years, one interval might be thirty million or more and the next only one or two hundred thousand. According to Schuchert, the known periods of glacial or semi-glacial climate have been approximately as follows:
List of Glacial Periods
Archeozoic.
(¼ of geological time or perhaps much more)
No known glacial periods.
Proterozoic.
(¼ of geological time)
a. Oldest known glacial period near base of Proterozoic in Canada. Evidence widely distributed.
b. Indian glacial period; time unknown.
c. African glacial period; time unknown.
d. Glaciation near end of Proterozoic in Australia, Norway, and China.
Paleozoic.
(¼ of geological time)
a. Late Ordovician(?). Local in Arctic Norway.
b. Silurian. Local in Alaska.
c. Early Devonian. Local in South Africa.
d. Early Permian. World-wide and very severe.
Mesozoic and Cenozoic.
(¼ of geological time)
a-b. None definitely determined during Mesozoic, although there appears to have been periods of cooling (a) in the late Triassic, and (b) in the late Cretacic, with at least local glaciation in early Eocene.
c. Severe glacial period during Pleistocene.
This table suggests an interesting inquiry. During the last few decades there has been great interest in ancient glaciation and geologists have carefully examined rocks of all ages for signs of glacial deposits. In spite of the large parts of the earth which are covered with deposits belonging to the Mesozoic and Cenozoic, which form the last quarter of geological time, the only signs of actual glaciation are those of the great Pleistocene period and a few local occurrences at the end of the Mesozoic or beginning of the Cenozoic. Late in the Triassic and early in the Jurassic, the climate appears to have been rigorous, although no tillites have been found to demonstrate glaciation. In the preceding quarter, that is, the Paleozoic, the Permian glaciation was more severe than that of the Pleistocene, and the Devonian than that of the Eocene, while the Ordovician evidences of low temperature are stronger than those at the end of the Triassic. In view of the fact that rocks of Paleozoic age cover much smaller areas than do those of later age, the three Paleozoic glaciations seem to indicate a relative frequency of glaciation. Going back to the Proterozoic, it is astonishing to find that evidence of two highly developed glacial periods, and possibly four, has been discovered. Since the Indian and the African glaciations of Proterozoic times are as yet undated, we cannot be sure that they are not of the same date as the others. Nevertheless, even two is a surprising number, for not only are most Proterozoic rocks so metamorphosed that possible evidences of glacial origin are destroyed, but rocks of that age occupy far smaller areas than either those of Paleozoic or, still more, Mesozoic and Cenozoic age. Thus the record of the last three-quarters of geological time suggests that if rocks of all ages were as abundant and as easily studied as those of the later periods, the frequency of glacial periods would be found to increase as one goes backward toward the beginnings of the earth’s history. This is interesting, for Jeans holds that the chances that the stars would approach one another were probably greater in the past than at present. This conclusion is based on the assumption that our universe is like the spiral nebulæ in which the orbits of the various members are nearly circular during the younger stages. Jeans considers it certain that in such cases the orbits will gradually become larger and more elliptical because of the attraction of one body for another. Thus as time goes on the stars will be more widely distributed and the chances of approach will diminish. If this is correct, the agreement between astronomical theory and geological conclusions suggests that the two are at least not in opposition.
The first quarter of geological time as well as the last three must be considered in this connection. During the Archeozoic, no evidence of glaciation has yet been discovered. This suggests that the geological facts disprove the astronomical theory. But our knowledge of early geological times is extremely limited, so limited that lack of evidence of glaciation in the Archeozoic may have no significance. Archeozoic rocks have been studied minutely over a very small percentage of the earth’s land surface. Moreover, they are highly metamorphosed so that, even if glacial tills existed, it would be hard to recognize them. Third, according to both the nebular and the planetesimal hypotheses, it seems possible that during the earliest stages of geological history the earth’s interior was somewhat warmer than now, and the surface may have been warmed more than at present by conduction, by lava flows, and by the fall of meteorites. If the earth during the Archeozoic period emitted enough heat to raise its surface temperature a few degrees, the heat would not prevent the development of low forms of life but might effectively prevent all glaciation. This does not mean that it would prevent changes of climate, but merely changes so extreme that their record would be preserved by means of ice. It will be most interesting to see whether future investigations in geology and astronomy indicate either a semi-uniform distribution of glacial periods throughout the past, or a more or less regular decrease in frequency from early times down to the present.
2. The Pleistocene glacial period was divided into at least four epochs, while in the Permian at least one inter-glacial epoch seems certain, and in some places the alternation between glacial and non-glacial beds suggests no less than nine. In the other glaciations the evidence is not yet clear. The question of periodicity is so important that it overthrows most glacial hypotheses. Indeed, had their authors known the facts as established in recent years, most of the hypotheses would never have been advanced. The carbon dioxide hypothesis is the only one which was framed with geologically rapid climatic alternations in mind. It certainly explains the facts of periodicity better than does any of its predecessors, but even so it does not account for the intimate way in which variations of all degrees from those of the weather up to glacial epochs seem to grade into one another.
According to our stellar hypothesis, occasional groups of glacial epochs would be expected to occur close together and to form long glacial periods. This is because many of the stars belong to groups or clusters in which the stars move in parallel paths. A good example is the cluster in the Hyades, where Boss has studied thirty-nine stars with special care.123 The stars are grouped about a center about 130 light years from the sun. The stars themselves are scattered over an area about thirty light years in diameter. They average about the same distance apart as do those near the sun, but toward the center of the group they are somewhat closer together. The whole thirty-nine sweep forward in essentially parallel paths. Boss estimates that 800,000 years ago the cluster was only half as far from the sun as at present, but probably that was as near as it has been during recent geological times. All of the thirty-nine stars of this cluster, as Moulton124 puts it, “are much greater in light-giving power than the sun. The luminosities of even the five smallest are from five to ten times that of the sun, while the largest are one hundred times greater in light-giving power than our own luminary. Their masses are probably much greater than that of the sun.” If the sun were to pass through such a cluster, first one star and then another might come so near as to cause a profound disturbance in the sun’s atmosphere.
3. Another important point upon which a glacial hypothesis may come to grief is the length of the periods or rather of the epochs which compose the periods. During the last or Pleistocene glacial period the evidence in America and Europe indicates that the inter-glacial epochs varied in length and that the later ones were shorter than the earlier. Chamberlin and Salisbury, from a comparison of various authorities, estimate that the intervals from one glacial epoch to another form a declining series, which may be roughly expressed as follows: 16-8-4-2-1, where unity is the interval from the climax of the late Wisconsin, or last glacial epoch, to the present. Most authorities estimate the culmination of the late Wisconsin glaciation as twenty or thirty thousand years ago. Penck estimates the length of the last inter-glacial period as 60,000 years and the preceding one as 240,000.125 R. T. Chamberlin, as already stated, finds that the consensus of opinion is that inter-glacial epochs have averaged five times as long as glacial epochs. The actual duration of the various glaciations probably did not vary in so great a ratio as did the intervals from one glaciation to another. The main point, however, is the irregularity of the various periods.
The relation of the stellar electrical hypothesis to the length of glacial epochs may be estimated from column C, in Table 5. There we see that the distances at which a star might possibly disturb the sun enough to cause glaciation range all the way from 120 billion miles in the case of a small star like the sun, to 3200 billion in the case of Betelgeuse, while for double stars the figure may rise a hundred times higher. From this we can calculate how long it would take a star to pass from a point where its influence would first amount to a quarter of the assumed maximum to a similar point on the other side of the sun. In making these calculations we will assume that the relative rate at which the star and the sun approach each other is about twenty-two miles per second, or 700 million miles per year, which is the average rate of motion of all the known stars. According to the distances in Table 5 this gives a range from about 500 years up to about 10,000, which might rise to a million in the case of double stars. Of course the time might be relatively short if the sun and a rapidly moving star were approaching one another almost directly, or extremely long if the sun and the star were moving in almost the same direction and at somewhat similar rates,—a condition more common than the other. Here, as in so many other cases, the essential point is that the figures which we thus obtain seem to be of the right order of magnitude.
4. Post-glacial climatic stages are so well known that in Europe they have definite names. Their sequence has already been discussed in Chapter XII. Fossils found in the peat bogs of Denmark and Scandinavia, for example, prove that since the final disappearance of the continental ice cap at the close of the Wisconsin there has been at least one period when the climate of Europe was distinctly milder than now. Directly overlying the sheets of glacial drift laid down by the ice there is a flora corresponding to that of the present tundras. Next come remains of a forest vegetation dominated by birches and poplars, showing that the climate was growing a little warmer. Third, there follow evidences of a still more favorable climate in the form of a forest dominated by pines; fourth, one where oak predominates; and fifth, a flora similar to that of the Black Forest of Germany, indicating that in Scandinavia the temperature was then decidedly higher than today. This fifth flora has retreated southward once more, having been driven back to its present latitude by a slight recurrence of a cool stormy climate.126 In central Asia evidence of post-glacial stages is found not only in five distinct moraines but in a corresponding series of elevated strands surrounding salt lakes and of river terraces in non-glaciated arid regions.127
In historic as well as prehistoric times, as we have already seen, there have been climatic fluctuations. For instance, the twelfth or thirteenth century B. C. appears to have been almost as mild as now, as does the seventh century B. C. On the other hand about 1000 B. C., at the time of Christ, and in the fourteenth century there were times of relative severity. Thus it appears that both on a large and on a small scale pulsations of climate are the rule. Any hypothesis of climatic changes must satisfy the periods of these pulsations. These conditions furnish a problem which makes difficulty for almost all hypotheses of climatic change. According to the present hypothesis, earth movements such as are discussed in Chapter XII may coöperate with two astronomical factors. One is the constant change in the positions of the stars, a change which we have already called kaleidoscopic, and the other is the fact that a large proportion of the stars are double or multiple. When one star in a group approaches the sun closely enough to cause a great solar disturbance, numerous others may approach or recede and have a minor effect. Thus, whenever the sun is near groups of stars we should expect that the earth would show many minor climatic pulsations and stages which might or might not be connected with glaciation. The historic pulsations shown in the curve of tree growth in California, Fig. 4, are the sort of changes that would be expected if movements of the stars have an effect on the solar atmosphere.
Not only are fully a third of all the visible stars double, as we have already seen, but at least a tenth of these are known to be triple or multiple. In many of the double stars the two bodies are close together and revolve so rapidly that whatever periodicity they might create in the sun’s atmosphere would be very short. In the triplets, however, the third star is ordinarily at least ten times as far from the other two as they are from each other, and its period of rotation sometimes runs into hundreds or thousands of years. An actual multiple star in the constellation Polaris will serve as an example. The main star is believed by Jeans to consist of two parts which are almost in contact and whirl around each other with extraordinary speed in four days. If this is true they must keep each other’s atmospheres in a state of intense commotion. Much farther away a third star revolves around this pair in twelve years. At a much greater distance a fourth star revolves around the common center of gravity of itself and the other three in a period which may be 20,000 years. Still more complicated cases probably exist. Suppose such a system were to traverse a path where it would exert a perceptible influence on the sun for thirty or forty thousand years. The varying movements of its members would produce an intricate series of cycles which might show all sorts of major and minor variations in length and intensity. Thus the varied and irregular stages of glaciation and the pulsations of historic times might be accounted for on the hypothesis of the proximity of the sun to a multiple star, as well as on that of the less pronounced approach and recession of a number of stars. In addition to all this, an almost infinitely complex series of climatic changes of long and short duration might arise if the sun passed through a nebula.
5. We have seen in Chapter VIII that the contrast between the somewhat severe climate of the present and the generally mild climate of the past is one of the great geological problems. The glacial period is not a thing of the distant past. Geologists generally recognize that it is still with us. Greenland and Antarctica are both shrouded in ice sheets in latitudes where fossil floras prove that at other periods the climate was as mild as in England or even New Zealand. The present glaciated regions, be it noted, are on the polar borders of the world’s two most stormy oceanic areas, just where ice would be expected to last longest according to the solar cyclonic hypothesis. In contrast with the semi-glacial conditions of the present, the last inter-glacial epoch was so mild that not only men but elephants and hippopotamuses flourished in central Europe, while at earlier times in the middle of long eras, such as the Paleozoic and Mesozoic, corals, cycads, and tree ferns flourished within the Arctic circle.
If the electro-stellar hypothesis of solar disturbances proves well founded, it may explain these peculiarities. Periods of mild climate would represent a return of the sun and the earth to their normal conditions of quiet. At such times the atmosphere of the sun is assumed to be little disturbed by sunspots, faculæ, prominences, and other allied evidences of movements; and the rice-grain structure is perhaps the most prominent of the solar markings. The earth at such times is supposed to be correspondingly free from cyclonic storms. Its winds are then largely of the purely planetary type, such as trade winds and westerlies. Its rainfall also is largely planetary rather than cyclonic. It falls in places such as the heat equator where the air rises under the influence of heat, or on the windward slopes of mountains, or in regions where warm winds blow from the ocean over cold lands.
According to the electro-stellar hypothesis, the conditions which prevailed during hundreds of millions of years of mild climate mean merely that the solar system was then in parts of the heavens where stars—especially double stars—were rare or small, and electrical disturbances correspondingly weak. Today, on the other hand, the sun is fairly near a number of stars, many of which are large doubles. Hence it is supposed to be disturbed, although not so much as at the height of the last glacial epoch.
After the preceding parts of this book had been written, the assistance of Dr. Schlesinger made it possible to test the electro-stellar hypothesis by comparing actual astronomical dates with the dates of climatic or solar phenomena. In order to make this possible, Dr. Schlesinger and his assistants have prepared Table 6, giving the position, magnitude, and motions of the thirty-eight nearest stars, and especially the date at which each was nearest the sun. In column 10 where the dates are given, a minus sign indicates the past and a plus sign the future. Dr. Shapley has kindly added column 12, giving the absolute magnitudes of the stars, that of the sun being 4.8, and column 13, showing their luminosity or absolute radiation, that of the sun being unity. Finally, column 14 shows the effective radiation received by the sun from each star when the star is at a minimum distance. Unity in this case is the effect of a star like the sun at a distance of one light year.
It is well known that radiation of all kinds, including light, heat, and electrical emissions, varies in direct proportion to the exposed surface, that is, as the square of the radius of a sphere, and inversely as the square of the distance. From black bodies, as we have seen, the total radiation varies as the fourth power of the absolute temperature. It is not certain that either light or electrical emissions from incandescent bodies vary in quite this same proportion, nor is it yet certain whether luminous and electrical emissions vary exactly together. Nevertheless they are closely related. Since the light coming from each star is accurately measured, while no information is available as to electrical emissions, we have followed Dr. Shapley’s suggestion and used the luminosity of the stars as the best available measure of total radiation. This is presumably an approximate measure of electrical activity, provided some allowance be made for disturbances by outside bodies such as companion stars. Hence the inclusion of column 14.
| TABLE 6 | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| THIRTY-EIGHT STARS HAVING LARGEST KNOWN PARALLAXES | ||||||||||||||
| (1) Right Ascension α 1900 | (2) Declination δ 1900 | (3) Visual Mag. m | (4) Spectrum | (5) Proper Motion | (6) Radial Velocity km. per sec. | (7) Present Parallax π | (8) Maximum Parallax | (9) Minimum Distance Light Yrs. | (10) Time of Minimum Distance | (11) Magnitude at Min. Dist. | (12) Absolute Magnitude | (13) Luminosity | (14) Effective radiation at minimum distance from sun | |
| Groombr. 34 | 0h12m.7 | +43°27’ | 8.1 | Ma | 2”.89 | + 3 | “.28 | “.28 | 11.6 | - 4000 | 8.1 | 10.3 | 0.0063 | 0.000051 |
| 128η Cassiop. | 43.0 | +57 17 | 3.6 | F8 | 1.24 | + 10 | .18 | .19 | 17.1 | - 47000 | 3.5 | 4.9 | 0.91 | 0.003110 |
| 43.9 | +4 55 | 12.3 | F0 | 3.01 | ..... | .24 | .... | .... | ....... | .... | 14.2 | 0.00017 | ........ | |
| 128κ Tucanæ | 1 12.4 | -69 24 | 5.0 | F8 | .39 | + 12 | .16 | .23 | 14.2 | -264000 | 4.2 | 6.0 | 0.33 | 0.001610 |
| τ Ceti | 39.4 | -16 28 | 3.6 | K0 | 1.92 | - 16 | .32 | .37 | 8.8 | + 46000 | 3.3 | 6.1 | 0.30 | 0.003840 |
| δ2 Eridani | 3 15.9 | -43 27 | 4.3 | G5 | 3.16 | + 87 | .16 | .22 | 14.8 | - 33000 | 3.6 | 5.3 | 0.63 | 0.002960 |
| 128ε Eridani | 28.2 | - 9 48 | 3.8 | K0 | .97 | + 16 | .31 | .46 | 7.1 | -106000 | 3.0 | 6.3 | 0.25 | 0.004970 |
| 12840(0)2 Eridani | 4 10.7 | - 7 49 | 4.5 | G5 | 4.08 | - 42 | .21 | .23 | 14.2 | + 19000 | 4.3 | 6.1 | 0.30 | 0.001470 |
| Cordoba Z. 243 | 5 7.7 | -44 59 | 9.2 | K2 | 8.75 | +242 | .32 | .68 | 4.8 | - 10000 | 7.6 | 11.7 | 0.0017 | 0.000074 |
| Weisse 592 | 26.4 | - 3 42 | 8.8 | K2 | 2.22 | ..... | .17 | .... | .... | ....... | .... | 9.9 | 0.009 | ........ |
| 128α Can. Maj. (Sirius) | 6 40.7 | -16 35 | -1.6 | A0 | 1.32 | - 8 | .37 | .41 | 8.0 | + 65000 | -1.8 | 1.2 | 27.50 | 0.429000 |
| 128α Can. Min. (Procyon) | 7 34.1 | + 5 29 | 0.5 | F5 | 1.24 | - 4 | .31 | .32 | 10.2 | + 34000 | 0.5 | 3.0 | 5.25 | 0.051300 |
| 128Fedorenko 1457-8 | 9 7.6 | +53 7 | 7.9 | Ma | 1.68 | + 10 | .16 | .16 | 20.4 | - 24000 | 7.9 | 8.9 | 0.023 | 0.000055 |
| Groombr. 1618 | 10 5.3 | +49 58 | 6.8 | K5p | 1.45 | - 30 | .18 | .23 | 14.2 | + 69000 | 6.3 | 8.1 | 0.048 | 0.000238 |
| Weisse 234 | 14.2 | +20 22 | 9.0 | ... | .49 | ..... | .19 | .... | .... | ....... | .... | 10.4 | 0.0057 | ........ |
| Lalande 21185 | 57.9 | +36 38 | 7.6 | Mb | 4.78 | - 87 | .41 | .76 | 4.3 | + 20000 | 6.2 | 10.7 | 0.0044 | 0.000238 |
| Lalande 21258 | 11 0.5 | +44 2 | 8.5 | K5 | 4.52 | + 65 | .19 | .22 | 14.8 | - 20000 | 8.2 | 9.9 | 0.009 | 0.000041 |
| 12.0 | -57 2 | 12.0 | ... | 2.69 | ..... | .34 | .... | .... | ........ | ... | 14.7 | 0.00011 | ........ | |
| Lalande 25372 | 13 40.7 | +15 26 | 8.5 | K5 | 2.30 | ..... | .19 | .... | .... | ....... | .... | 9.9 | 0.009 | ........ |
| 128α Centauri | 14 32.8 | -60 25 | 0.2 | G | 3.68 | + 22 | .76 | 1.03 | 3.2 | - 28000 | -0.5 | 4.6 | 1.20 | 0.117500 |
| 128ξ Bootes | 14 46.8 | +19 31 | 4.6 | K5p | .17 | + 4 | .17 | .22 | 14.8 | -598000 | 4.0 | 5.8 | 0.40 | 0.001815 |
| 128Lalande 27173 | 51.6 | -20 58 | 5.8 | Kp | 1.96 | + 20 | .18 | .19 | 17.1 | - 36000 | 5.6 | 7.1 | 0.12 | 0.000412 |
| Weisse 1259 | 16 41.4 | +33 41 | 8.4 | ... | .37 | ..... | .18 | .... | .... | ....... | .... | 9.7 | 0.011 | ........ |
| Lacaille 7194 | 17 11.5 | -46 32 | 5.7 | K | .97 | ..... | .19 | .... | .... | ....... | .... | 7.1 | 0.12 | ........ |
| 128β 416 | 12.1 | -34 53 | 5.9 | K5 | 1.19 | - 4 | .17 | .17 | 19.2 | + 21000 | 5.7 | 7.1 | 0.12 | 0.000329 |
| Argel -0.17415-6 | 37.0 | +68 26 | 9.1 | K | 1.33 | ..... | .22 | .... | .... | ....... | .... | 10.8 | 0.004 | ........ |
| Barnard’s star | 52.9 | + 4 25 | 9.7 | Mb | 10.30 | - 80 | .53 | .70 | 4.7 | + 10000 | 9.1 | 13.3 | 0.0025 | 0.000114 |
| 12870p Ophiuchi | 18 0.4 | + 2 31 | 4.3 | K | 1.13 | ..... | .19 | .... | .... | ....... | .... | 5.7 | 0.44 | ........ |
| 128Σ 2398 | 41.7 | +59 29 | 8.8 | K | 2.31 | ..... | .29 | .... | .... | ....... | .... | 11.1 | 0.0030 | ........ |
| σ Draconis | 19 32.5 | +69 29 | 4.8 | G5 | 1.84 | + 26 | .20 | .23 | 14.2 | - 49000 | 4.5 | 6.3 | 0.25 | 0.001238 |
| 128α Aquilæ (Altair) | 45.9 | + 8 36 | 1.2 | A5 | .66 | - 33 | .21 | .51 | 6.4 | +117000 | -0.7 | 2.8 | 6.30 | 0.153600 |
| 12861 Cygni | 21 2.4 | +38 15 | 5.6 | K5 | 5.20 | - 64 | .30 | .38 | 8.6 | + 19000 | 5.1 | 8.0 | 0.053 | 0.000715 |
| Lacaille 8760 | 11.4 | -39 15 | 6.6 | G | 3.53 | + 13 | .25 | .26 | 12.6 | - 11000 | 6.6 | 8.6 | 0.030 | 0.000189 |
| ε Indi | 55.7 | -57 12 | 4.8 | K5 | 4.70 | - 39 | .28 | .31 | 10.5 | + 17000 | 4.6 | 7.0 | 0.13 | 0.001230 |
| 128Krüger 60 | 22 24.4 | +57 12 | 9.2 | ... | .87 | ..... | .26 | .... | .... | ....... | .... | 11.3 | 0.0025 | ....... |
| Lacaille 9352 | 59.4 | -36 26 | 7.1 | K | 6.90 | + 12 | .29 | .29 | 11.2 | - 3000 | 7.1 | 9.4 | 0.014 | 0.000111 |
| Lalande 46650 | 23 44.0 | + 1 52 | 8.7 | Ma | 1.39 | ..... | .17 | .... | .... | ....... | .... | 9.9 | 0.009 | ....... |
| C. G. A. 32416 | 59.5 | -37 51 | 8.2 | G | 6.05 | + 26 | .22 | .22 | 14.8 | - 7000 | 8.2 | 9.9 | 0.009 | 0.000041 |
On the basis of column 14 and of the movements and distances of the stars as given in the other columns Fig. 10 has been prepared. This gives an estimate of the approximate electrical energy received by the sun from the nearest stars for 70,000 years before and after the present. It is based on the twenty-six stars for which complete data are available in Table 6. The inclusion of the other twelve would not alter the form of the curve, for even the largest of them would not change any part by more than about half of 1 per cent, if as much. Nor would the curve be visibly altered by the omission of all except four of the twenty-six stars actually used. The four that are important, and their relative luminosity when nearest the sun, are Sirius 429,000, Altair 153,000, Alpha Centauri 117,500, and Procyon 51,300. The figure for the next star is only 4970, while for this star combined with the other twenty-one that are unimportant it is only 24,850.
Figure 10 is not carried more than 70,000 years into the past or into the future because the stars near the sun at more remote times are not included among the thirty-eight having the largest known parallaxes. That is, they have either moved away or are not yet near enough to be included. Indeed, as Dr. Schlesinger strongly emphasizes, there may be swiftly moving, bright or gigantic stars which are now quite far away, but whose inclusion would alter Fig. 10 even within the limits of the 140,000 years there shown. It is almost certain, however, that the most that these would do would be to raise, but not obliterate, the minima on either side of the main maximum.
In preparing Fig. 10 it has been necessary to make allowance for double stars. Passing by the twenty-two unimportant stars, it appears that the companion of Sirius is eight or ten magnitudes smaller than that star, while the companions of Procyon and Altair are five or more magnitudes smaller than their bright comrades. This means that the luminosity of the faint components is at most only 1 per cent of that of their bright companions and in the case of Sirius not a hundredth of 1 per cent. Hence their inclusion would have no visible effect on Fig. 10. In Alpha Centauri, on the other hand, the two components are of almost the same magnitude. For this reason the effective radiation of that star as given in column 14 is doubled in Fig. 10, while for another reason it is raised still more. The other reason is that if our inferences as to the electrical effect of the sun on the earth and of the planets on the sun are correct, double stars, as we have seen, must be much more effective electrically than single stars. By the same reasoning two bright stars close together must excite one another much more than a bright star and a very faint one, even if the distances in both cases are the same. So, too, other things being equal, a triple star must be more excited electrically than a double star. Hence in preparing Fig. 10 all double stars receive double weight and each part of Alpha Centauri receives an additional 50 per cent because both parts are bright and because they have a third companion to help in exciting them.
According to the electro-stellar hypothesis, Alpha Centauri is more important climatically than any other star in the heavens not only because it is triple and bright, but because it is the nearest of all stars, and moves fairly rapidly. Sirius and Procyon move slowly in respect to the sun, only about eleven and eight kilometers per second respectively, and their distances at minimum are fairly large, that is, 8 and 10.2 light years. Hence their effect on the sun changes slowly. Altair moves faster, about twenty-six kilometers per second, and its minimum distance is 6.4 light years, so that its effect changes fairly rapidly. Alpha Centauri moves about twenty-four kilometers per second, and its minimum distance is only 3.2 light years. Hence its effect changes very rapidly, the change in its apparent luminosity as seen from the sun amounting at maximum to about 30 per cent in 10,000 years against 14 per cent for Altair, 4 for Sirius, and 2 for Procyon. The vast majority of the stars change so much more slowly than even Procyon that their effect is almost uniform. All the stars at a distance of more than perhaps twenty or thirty light years may be regarded as sending to the sun a practically unchanging amount of radiation. It is the bright stars within this limit which are important, and their importance increases with their proximity, their speed of motion, and the brightness and number of their companions. Hence Alpha Centauri causes the main maximum in Fig. 10, while Sirius, Altair, and Procyon combine to cause a general rise of the curve from the past to the future.
Let us now interpret Fig. 10 geologically. The low position of the curve fifty to seventy thousand years ago suggests a mild inter-glacial climate distinctly less severe than that of the present. Geologists say that such was the case. The curve suggests a glacial epoch culminating about 28,000 years ago. The best authorities put the climax of the last glacial epoch between twenty-five and thirty thousand years ago. The curve shows an amelioration of climate since that time, although it suggests that there is still considerable severity. The retreat of the ice from North America and Europe, and its persistence in Greenland and Antarctica agree with this. And the curve indicates that the change of climate is still persisting, a conclusion in harmony with the evidence as to historic changes.
If Alpha Centauri is really so important, the effect of its variations, provided it has any, ought perhaps to be evident in the sun. The activity of the star’s atmosphere presumably varies, for the orbits of the two components have an eccentricity of 0.51. Hence during their period of revolution, 81.2 years, the distance between them ranges from 1,100,000,000 to 3,300,000,000 miles. They were at a minimum distance in 1388, 1459, 1550, 1631, 1713, 1794, 1875, and will be again in 1956. In Fig. 11, showing sunspot variations, it is noticeable that the years 1794 and 1875 come just at the ends of periods of unusual solar activity, as indicated by the heavy horizontal line. A similar period of great activity seems to have begun about 1914. If its duration equals the average of its two predecessors, it will end about 1950. Back in the fourteenth century a period of excessive solar activity, which has already been described, culminated from 1370 to 1385, or just before the two parts of Alpha Centauri were at a minimum distance. Thus in three and perhaps four cases the sun has been unusually active during a time when the two parts of the star were most rapidly approaching each other and when their atmospheres were presumably most disturbed and their electrical emanations strongest.
The fact that Alpha Centauri, the star which would be expected most strongly to influence the sun, and hence the earth, was nearest the sun at the climax of the last glacial epoch, and that today the solar atmosphere is most active when the star is presumably most disturbed may be of no significance. It is given for what it is worth. Its importance lies not in the fact that it proves anything, but that no contradiction is found when we test the electro-stellar hypothesis by facts which were not thought of when the hypothesis was framed. A vast amount of astronomical work is still needed before the matter can be brought to any definite conclusion. In case the hypothesis stands firm, it may be possible to use the stars as a help in determining the exact chronology of the later part of geological times. If the hypothesis is disproved, it will merely leave the question of solar variations where it is today. It will not influence the main conclusions of this book as to the causes and nature of climatic changes. Its value lies in the fact that it calls attention to new lines of research.
Note. The asterisks indicate two absolute minima of sunspots in 1810 and 1913, and the middle years (1780 and 1854) of two periods when the sunspot maxima never fell below 95. If Alpha Centauri has an effect on the sun’s atmosphere, the end of another such period would be expected not far from 1957.