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The Effect Of Other Bodies On The Sun

If solar activity is really an important factor in causing climatic

changes, it behooves us to subject the sun to the same kind of inquiry

to which we have subjected the earth. We have inquired into the nature

of the changes through which the earth's crust, the oceans, and the

atmosphere have influenced the climate of geological times. It has not

been necessary, however, to study the origin of the earth, nor to trace

s earlier stages. Our study of the geological record begins only when

the earth had attained practically its present mass, essentially its

present shape, and a climate so similar to that of today that life as we

know it was possible. In other words, the earth had passed the stages of

infancy, childhood, youth, and early maturity, and had reached full

maturity. As it still seems to be indefinitely far from old age, we

infer that during geological times its relative changes have been no

greater than those which a man experiences between the ages of perhaps

twenty-five and forty.

Similar reasoning applies with equal or greater force to the sun.

Because of its vast size it presumably passes through its stages of

development much more slowly than the earth. In the first chapter of

this book we saw that the earth's relative uniformity of climate for

hundreds of millions of years seems to imply a similar uniformity in

solar activity. This accords with a recent tendency among astronomers

who are more and more recognizing that the stars and the solar system

possess an extraordinary degree of conservatism. Changes that once were

supposed to take place in thousands of years are now thought to have

required millions. Hence in this chapter we shall assume that throughout

geological times the condition of the sun has been almost as at present.

It may have been somewhat larger, or different in other ways, but it was

essentially a hot, gaseous body such as we see today and it gave out

essentially the same amount of energy. This assumption will affect the

general validity of what follows only if it departs widely from the

truth. With this assumption, then, let us inquire into the degree to

which the sun's atmosphere has probably been disturbed throughout

geological times.

In Earth and Sun, as already explained, a detailed study has led to

the conclusion that cyclonic storms are influenced by the electrical

action of the sun. Such action appears to be most intense in sunspots,

but apparently pertains also to other disturbed areas in the sun's

atmosphere. A study of sunspots suggests that their true periodicity is

almost if not exactly identical with that of the orbital revolution of

Jupiter, 11.8 years. Other investigations show numerous remarkable

coincidences between sunspots and the orbital revolution of the other

planets, including especially Saturn and Mercury. This seems to indicate

that there is some truth in the hypothesis that sunspots and other

related disturbances of the solar atmosphere owe their periodicity to

the varying effects of the planets as they approach and recede from the

sun in their eccentric orbits and as they combine or oppose their

effects according to their relative positions. This does not mean that

the energy of the solar disturbances is supposed to come from the

planets, but merely that their variations act like the turning of a

switch to determine when and how violently the internal forces of the

sun shall throw the solar atmosphere into commotion. This hypothesis is

by no means new, for in one form or another it has been advocated by

Wolfer, Birkeland, E. W. Brown, Schuster, Arctowski, and others.

The agency through which the planets influence the solar atmosphere is

not yet clear. The suggested agencies are the direct pull of

gravitation, the tidal effect of the planets, and an electro-magnetic

effect. In Earth and Sun the conclusion is reached that the first two

are out of the question, a conclusion in which E. W. Brown acquiesces.

Unless some unknown cause is appealed to, this leaves an

electro-magnetic hypothesis as the only one which has a reasonable

foundation. Schuster inclines to this view. The conclusions set forth in

Earth and Sun as to the electrical nature of the sun's influence on

the earth point somewhat in the same direction. Hence in this chapter we

shall inquire what would happen to the sun, and hence to the earth, on

their journey through space, if the solar atmosphere is actually subject

to disturbance by the electrical or other effects of other heavenly

bodies. It need hardly be pointed out that we are here venturing into

highly speculative ground, and that the verity or falsity of the

conclusions reached in this chapter has nothing to do with the validity

of the reasoning in previous chapters. Those chapters are based on the

assumption that terrestrial causes of climatic changes are supplemented

by solar disturbances which produce their effect partly through

variations in temperature but also through variations in the intensity

and paths of cyclonic storms. The present chapter seeks to shed some

light on the possible causes and sequence of solar disturbances.

Let us begin by scanning the available evidence as to solar disturbances

previous to the time when accurate sunspot records are available. Two

rather slender bits of evidence point to cycles of solar activity

lasting hundreds of years. One of these has already been discussed in

Chapter VI, where the climatic stress of the fourteenth century was

described. At that time sunspots are known to have been unusually

numerous, and there were great climatic extremes. Lakes overflowed in

Central Asia; storms, droughts, floods, and cold winters were unusually

severe in Europe; the Caspian Sea rose with great rapidity; the trees of

California grew with a vigor unknown for centuries; the most terrible of

recorded famines occurred in England and India; the Eskimos were

probably driven south by increasing snowiness in Greenland; and the

Mayas of Yucatan appear to have made their last weak attempt at a

revival of civilization under the stimulus of greater storminess and

less constant rainfall.

The second bit of evidence is found in recent exhaustive studies of

periodicities by Turner[112] and other astronomers. They have sought

every possible natural occurrence for which a numerical record is

available for a long period. The most valuable records appear to be

those of tree growth, Nile floods, Chinese earthquakes, and sunspots.

Turner reaches the conclusion that all four types of phenomena show the

same periodicity, namely, cycles with an average length of about 260 to

280 years. He suggests that if this is true, the cycles in tree growth

and in floods, both of which are climatic, are probably due to a

non-terrestrial cause. The fact that the sunspots show similar cycles

suggests that the sun's variations are the cause.

These two bits of evidence are far too slight to form the foundation of

any theory as to changes in solar activity in the geological past.

Nevertheless it may be helpful to set forth certain possibilities as a

stimulus to further research. For example, it has been suggested that

meteoric bodies may have fallen into the sun and caused it suddenly to

flare up, as it were. This is not impossible, although it does not

appear to have taken place since men became advanced enough to make

careful observations. Moreover, the meteorites which now fall on the

earth are extremely small, the average size being computed as no larger

than a grain of wheat. The largest ever found on the earth's surface, at

Bacubirito in Mexico, weighs only about fifty tons, while within the

rocks the evidences of meteorites are extremely scanty and

insignificant. If meteorites had fallen into the sun often enough and of

sufficient size to cause glacial fluctuations and historic pulsations of

climate, it seems highly probable that the earth would show much more

evidence of having been similarly disturbed. And even if the sun should

be bombarded by large meteors the result would probably not be sudden

cold periods, which are the most notable phenomena of the earth's

climatic history, but sudden warm periods followed by slow cooling.

Nevertheless, the disturbance of the sun by collision with meteoric

matter can by no means be excluded as a possible cause of climatic


Allied to the preceding hypothesis is Shapley's[113] nebular hypothesis.

At frequent intervals, averaging about once a year during the last

thirty years, astronomers have discovered what are known as novae. These

are stars which were previously faint or even invisible, but which flash

suddenly into brilliancy. Often their light-giving power rises seven or

eight magnitudes--a thousand-fold. In addition to the spectacular novae

there are numerous irregular variables whose brilliancy changes in every

ratio from a few per cent up to several magnitudes. Most of them are

located in the vicinity of nebulae, as is also the case with novae. This,

as well as other facts, makes it probable that all these stars are

"friction variables," as Shapley calls them. Apparently as they pass

through the nebulae they come in contact with its highly diffuse matter

and thereby become bright much as the earth would become bright if its

atmosphere were filled with millions of almost infinitesimally small

meteorites. A star may also lose brilliancy if nebulous matter

intervenes between it and the observer. If our sun has been subjected to

any of these changes some sort of climatic effect must have been


In a personal communication Shapley amplifies the nebular climatic

hypothesis as follows:

Within 700 light years of the sun in many directions (Taurus,

Cygnus, Ophiuchus, Scorpio) are great diffuse clouds of nebulosity,

some bright, most of them dark. The probability that stars moving in

the general region of such clouds will encounter this material is

very high, for the clouds fill enormous volumes of space,--e.g.,

probably more than a hundred thousand cubic light years in the Orion

region, and are presumably composed of rarefied gases or of dust

particles. Probably throughout all our part of space such nebulosity

exists (it is all around us, we are sure), but only in certain

regions is it dense enough to affect conspicuously the stars

involved in it. If a star moving at high velocity should collide

with a dense part of such a nebulous cloud, we should probably have

a typical nova. If the relative velocity of nebulous material and

star were low or moderate, or if the material were rare, we should

not expect a conspicuous effect on the star's light.

In the nebulous region of Orion, which is probably of unusually high

density, there are about 100 known stars, varying between 20% and

80% of their total light--all of them irregularly--some slowly, some

suddenly. Apparently they are "friction variables." Some of the

variables suddenly lose 40% of their light as if blanketed by

nebulous matter. In the Trifid Nebula there are variables like those

of Orion, in Messier 8 also, and probably many of the 100 or so

around the Rho Ophiuchi region belong to this kind.

I believe that our sun could not have been a typical nova, at least

not since the Archeozoic, that is for perhaps a billion years. I

believe we have in geological climates final proof of this, because

an increase in the amount of solar radiation by 1000 times as in the

typical nova, would certainly punctuate emphatically the life cycle

on the earth, even if the cause of the nova would not at the same

time eliminate the smaller planets. But the sun may have been one of

these miniature novae or friction variables; and I believe it very

probable that its wanderings through this part of space could not

long leave its mean temperature unaffected to the amount of a few

per cent.

One reason we have not had this proposal insisted upon before is

that the data back of it are mostly new--the Orion variables have

been only recently discovered and studied, the distribution and

content of the dark nebulae are hardly as yet generally known.

This interesting hypothesis cannot be hastily dismissed. If the sun

should pass through a nebula it seems inevitable that there would be at

least slight climatic effects and perhaps catastrophic effects through

the action of the gaseous matter not only on the sun but on the earth's

own atmosphere. As an explanation of the general climatic conditions of

the past, however, Shapley points out that the hypothesis has the

objection of being vague, and that nebulosity should not be regarded as

more than "a possible factor." One of the chief difficulties seems to be

the enormously wide distribution of as yet undiscovered nebulous matter

which must be assumed if any large share of the earth's repeated

climatic changes is to be ascribed to such matter. If such matter is

actually abundant in space, it is hard to see how any but the nearest

stars would be visible. Another objection is that there is no known

nebulosity near at hand with which to connect the climatic vicissitudes

of the last glacial period. Moreover, the known nebulae are so much less

numerous than stars that the chances that the sun will encounter one of

them are extremely slight. This, however, is not an objection, for

Shapley points out that during geological times the sun can never have

varied as much as do the novae, or even as most of the friction

variables. Thus the hypothesis stands as one that is worth

investigating, but that cannot be finally rejected or accepted until it

is made more definite and until more information is available.

Another suggested cause of solar variations is the relatively sudden

contraction of the sun such as that which sometimes occurs on the earth

when continents are uplifted and mountains upheaved. It seems improbable

that this could have occurred in a gaseous body like the sun. Lacking,

as it does, any solid crust which resists a change of form, the sun

probably shrinks steadily. Hence any climatic effects thus produced must

be extremely gradual and must tend steadily in one direction for

millions of years.

Still another suggestion is that the tidal action of the stars and other

bodies which may chance to approach the sun's path may cause

disturbances of the solar atmosphere. The vast kaleidoscope of space is

never quiet. The sun, the stars, and all the other heavenly bodies are

moving, often with enormous speed. Hence the effect of gravitation upon

the sun must vary constantly and irregularly, as befits the geological

requirements. In the case of the planets, however, the tidal effect does

not seem competent to produce the movements of the solar atmosphere

which appear to be concerned in the inception of sunspots. Moreover,

there is only the most remote probability that a star and the sun will

approach near enough to one another to produce a pronounced

gravitational disturbance in the solar atmosphere. For instance, if it

be assumed that changes in Jupiter's tidal effect on the sun are the

main factor in regulating the present difference between sunspot maxima

and sunspot minima, the chances that a star or some non-luminous body of

similar mass will approach near enough to stimulate solar activity and

thereby bring on glaciation are only one in twelve billion years, as

will be explained below. This seems to make a gravitational hypothesis


Another possible cause of solar disturbances is that the stars in their

flight through space may exert an electrical influence which upsets the

equilibrium of the solar atmosphere. At first thought this seems even

more impossible than a gravitational effect. Electrostatic effects,

however, differ greatly from those of tides. They vary as the diameter

of a body instead of as its mass; their differentials also vary

inversely as the square of the distance instead of as the cube.

Electrostatic effects also increase as the fourth power of the

temperature or at least would do so if they followed the law of black

bodies; they are stimulated by the approach of one body to another; and

they are cumulative, for if ions arrive from space they must accumulate

until the body to which they have come begins to discharge them. Hence,

on the basis of assumptions such as those used in the preceding

paragraph, the chances of an electrical disturbance of the solar

atmosphere sufficient to cause glaciation on the earth may be as high as

one in twenty or thirty million years. This seems to put an electrical

hypothesis within the bounds of possibility. Further than that we cannot

now go. There may be other hypotheses which fit the facts much better,

but none seems yet to have been suggested.

In the rest of this chapter the tidal and electrical hypotheses of

stellar action on the sun will be taken up in detail. The tidal

hypothesis is considered because in discussions of the effect of the

planets it has hitherto held almost the entire field. The electrical

hypothesis will be considered because it appears to be the best yet

suggested, although it still seems doubtful whether electrical effects

can be of appreciable importance over such vast distances as are

inevitably involved. The discussion of both hypotheses will necessarily

be somewhat technical, and will appeal to the astronomer more than to

the layman. It does not form a necessary part of this book, for it has

no bearing on our main thesis of the effect of the sun on the earth. It

is given here because ultimately the question of changes in solar

activity during geological times must be faced.

In the astronomical portion of the following discussion we shall follow

Jeans[114] in his admirable attempt at a mathematical analysis of the

motions of the universe. Jeans divides the heavenly bodies into five

main types. (1) Spiral nebulae, which are thought by some astronomers to

be systems like our own in the making, and by others to be independent

universes lying at vast distances beyond the limits of our Galactic

universe, as it is called from the Galaxy or Milky Way. (2) Nebulae of a

smaller type, called planetary. These lie within the Galactic portion of

the universe and seem to be early stages of what may some day be stars

or solar systems. (3) Binary or multiple stars, which are

extraordinarily numerous. In some parts of the heavens they form 50 or

even 60 per cent of the stars and in the galaxy as a whole they seem to

form "fully one third." (4) Star clusters. These consist of about a

hundred groups of stars in each of which the stars move together in the

same direction with approximately the same velocity. These, like the

spiral nebulae, are thought by some astronomers to lie outside the limits

of the galaxy, but this is far from certain. (5) The solar system.

According to Jeans this seems to be unique. It does not fit into the

general mathematical theory by which he explains spiral nebulae,

planetary nebulae, binary stars, and star clusters. It seems to demand a

special explanation, such as is furnished by tidal disruption due to the

passage of the sun close to another star.

The part of Jeans' work which specially concerns us is his study of the

probability that some other star will approach the sun closely enough to

have an appreciable gravitative or electrical effect, and thus cause

disturbances in the solar atmosphere. Of course both the star and the

sun are moving, but to avoid circumlocution we shall speak of such

mutual approaches simply as approaches of the sun. For our present

purpose the most fundamental fact may be summed up in a quotation from

Jeans in which he says that most stars "show evidence of having

experienced considerable disturbance by other systems; there is no

reason why our solar system should be expected to have escaped the

common fate." Jeans gives a careful calculation from which it is

possible to derive some idea of the probability of any given degree of

approach of the sun and some other star. Of course all such calculations

must be based on certain assumptions. The assumptions made by Jeans are

such as to make the probability of close approaches as great as

possible. For example, he allows only 560 million years for the entire

evolution of the sun, whereas some astronomers and geologists would put

the figure ten or more times as high. Nevertheless, Jeans' assumptions

at least show the order of magnitude which we may expect on the basis of

reasonable astronomical conclusions.

According to the planetary hypothesis of sunspots, the difference in the

effect of Jupiter when it is nearest and farthest from the sun is the

main factor in starting the sunspot cycle and hence the corresponding

terrestrial cycle. The climatic difference between sunspot maxima and

minima, as measured by temperature, apparently amounts to at least a

twentieth and perhaps a tenth of the difference between the climate of

the last glacial epoch and the present. We may suppose, then, that a

body which introduced a gravitative or electrical factor twenty times as

great as the difference in Jupiter's effect at its maximum and minimum

distances from the sun would cause a glacial epoch if the effect lasted

long enough. Of course the other planets combine their effects with that

of Jupiter, but for the sake of simplicity we will leave the others out

of account. The difference between Jupiter's maximum and minimum tidal

effect on the sun amounts to 29 per cent of the planet's average effect.

The corresponding difference, according to the electrical hypothesis, is

about 19 per cent, for electrostatic action varies as the square of the

distance instead of as the cube. Let us assume that a body exerting four

times Jupiter's present tidal effect and placed at the average distance

of Jupiter from the sun would disturb the sun's atmosphere twenty times

as much as the present difference between sunspot maxima and minima, and

thus, perhaps, cause a glacial period on the earth.

On the basis of this assumption our first problem is to estimate the

frequency with which a star, visible or dark, is likely to approach near

enough to the sun to produce a tidal effect four times that of

Jupiter. The number of visible stars is known or at least well

estimated. As to dark stars, which have grown cool, Arrhenius believed

that they are a hundred times as numerous as bright stars; few

astronomers believe that there are less than three or four times as

many. Dr. Shapley of the Harvard Observatory states that a new

investigation of the matter suggests that eight or ten is probably a

maximum figure. Let us assume that nine is correct. The average visible

star, so far as measured, has a mass about twice that of the sun, or

about 2100 times that of Jupiter. The distances of the stars have been

measured in hundreds of cases and thus we can estimate how many stars,

both visible and invisible, are on an average contained in a given

volume of space. On this basis Jeans estimates that there is only one

chance in thirty billion years that a visible star will approach within

2.8 times the distance of Neptune from the sun, that is, within about

eight billion miles. If we include the invisible stars the chances

become one in three billion years. In order to produce four times the

tidal effect of Jupiter, however, the average star would have to

approach within about four billion miles of the sun, and the chances of

that are only one in twelve billion years. The disturbing star would be

only 40 per cent farther from the sun than Neptune, and would almost

pass within the solar system.

Even though Jeans holds that the frequency of the mutual approach of the

sun and a star was probably much greater in the distant past than at

present, the figures just given lend little support to the tidal

hypothesis. In fact, they apparently throw it out of court. It will be

remembered that Jeans has made assumptions which give as high a

frequency of stellar encounters as is consistent with the astronomical

facts. We have assumed nine dark stars for every bright one, which may

be a liberal estimate. Also, although we have assumed that a disturbance

of the sun's atmosphere sufficient to cause a glacial period would arise

from a tidal effect only twenty times as great as the difference in

Jupiter's effect when nearest the sun and farthest away, in our

computations this has actually been reduced to thirteen. With all these

favorable assumptions the chances of a stellar approach of the sort here

described are now only one in twelve billion years. Yet within a hundred

million years, according to many estimates of geological time, and

almost certainly within a billion, there have been at least half a dozen


Our use of Jeans' data interposes another and equally insuperable

difficulty to any tidal hypothesis. Four billion miles is a very short

distance in the eyes of an astronomer. At that distance a star twice the

size of the sun would attract the outer planets more strongly than the

sun itself, and might capture them. If a star should come within four

billion miles of the sun, its effect in distorting the orbits of all the

planets would be great. If this had happened often enough to cause all

the glaciations known to geologists, the planetary orbits would be

strongly elliptical instead of almost circular. The consideration here

advanced militate so strongly against the tidal hypothesis of solar

disturbances that it seems scarcely worth while to consider it further.

Let us turn now to the electrical hypothesis. Here the conditions are

fundamentally different from those of the tidal hypothesis. In the first

place the electrostatic effect of a body has nothing to do with its

mass, but depends on the area of its surface; that is, it varies as the

square of the radius. Second, the emission of electrons varies

exponentially. If hot glowing stars follow the same law as black bodies

at lower temperatures, the emission of electrons, like the emission of

other kinds of energy, varies as the fourth power of the absolute

temperature. In other words, suppose there are two black bodies,

otherwise alike, but one with a temperature of 27 deg. C. or 300 deg. on the

absolute scale, and the other with 600 deg. on the absolute scale. The

temperature of one is twice as high as that of the other, but the

electrostatic effect will be sixteen times as great.[115] Third, the

number of electrons that reach a given body varies inversely as the

square of the distance, instead of as the cube which is the case with

tide-making forces.

In order to use these three principles in calculating the effect of the

stars we must know the diameters, distances, temperature, and number of

the stars. The distances and number may safely be taken as given by

Jeans in the calculations already cited. As to the diameters, the

measurements of the stars thus far made indicate that the average mass

is about twice that of the sun. The average density, as deduced by

Shapley[116] from the movements of double stars, is about one-eighth the

solar density. This would give an average diameter about two and a half

times that of the sun. For the dark stars, we shall assume for

convenience that they are ten times as numerous as the bright ones. We

shall also assume that their diameter is half that of the sun, for being

cool they must be relatively dense, and that their temperature is the

same as that which we shall assume for Jupiter.

As to Jupiter we shall continue our former assumption that a body with

four times the effectiveness of that planet, which here means with twice

as great a radius, would disturb the sun enough to cause glaciation. It

would produce about twenty times the electrostatic effect which now

appears to be associated with the difference in Jupiter's effect at

maximum and minimum. The temperature of Jupiter must also be taken into

account. The planet is supposed to be hot because its density is low,

being only about 1.25 that of water. Nevertheless, it is probably not

luminous, for as Moulton[117] puts it, shadows upon it are black and its

moons show no sign of illumination except from the sun. Hence a

temperature of about 600 deg.C., or approximately 900 deg. on the absolute

scale, seems to be the highest that can reasonably be assigned to the

cold outer layer whence electrons are emitted. As to the temperature of

the sun, we shall adopt the common estimate of about 6300 deg.C. on the

absolute scale. The other stars will be taken as averaging the same,

although of course they vary greatly.

When Jeans' method of calculating the probability of a mutual approach

of the sun and a star is applied to the assumptions given above, the

results are as shown in Table 5. On that basis the dark stars seem to be

of negligible importance so far as the electrical hypothesis is

concerned. Even though they may be ten times as numerous as the bright

ones there appears to be only one chance in 130 billion years that one

of them will approach the sun closely enough to cause the assumed

disturbance of the solar atmosphere. On the other hand, if all the

visible stars were the size of the sun, and as hot as that body, their

electrical effect would be fourfold that of our assumed dark star

because of their size, and 2401 times as great because of their

temperature, or approximately 10,000 times as great. Under such

conditions the theoretical chance of an approach that would cause

glaciation is one in 130 million years. If the average visible star is

somewhat cooler than the sun and has a radius about two and one-half

times as great, as appears to be the fact, the chances rise to one in

thirty-eight million years. A slight and wholly reasonable change in our

assumptions would reduce this last figure to only five or ten million.

For instance, the earth's mean temperature during the glacial period has

been assumed as 10 deg.C. lower than now, but the difference may have been

only 6 deg.. Again, the temperature of the outer atmosphere of Jupiter where

the electrons are shot out may be only 500 deg. or 700 deg. absolute, instead of

900 deg.. Or the diameter of the average star may be five or ten times that

of the sun, instead of only two and one-half times as great. All this,

however, may for the present be disregarded. The essential point is that

even when the assumptions err on the side of conservatism, the results

are of an order of magnitude which puts the electrical hypothesis within

the bounds of possibility, whereas similar assumptions put the tidal

hypothesis, with its single approach in twelve billion years, far beyond

those limits.

The figures for Betelgeuse in Table 5 are interesting. At a meeting of

the American Association for the Advancement of Science in December,

1920, Michelson reported that by measurements of the interference of

light coming from the two sides of that bright star in Orion, the

observers at Mount Wilson had confirmed the recent estimates of three

other authorities that the star's diameter is about 218 million miles,

or 250 times that of the sun. If other stars so much surpass the

estimates of only a decade or two ago, the average diameter of all the

visible stars must be many times that of the sun. The low figure for

Betelgeuse in section D of the table means that if all the stars were as

large as Betelgeuse, several might often be near enough to cause

profound disturbances of the solar atmosphere. Nevertheless, because of

the low temperature of the giant red stars of the Betelgeuse type, the

distance at which one of them would produce a given electrical effect is

only about five times the distance at which our assumed average star

would produce the same effect. This, to be sure, is on the assumption

that the radiation of energy from incandescent bodies varies according

to temperature in the same ratio as the radiation from black bodies.

Even if this assumption departs somewhat from the truth, it still seems

almost certain that the lower temperature of the red compared with the

high temperature of the white stars must to a considerable degree reduce

the difference in electrical effect which would otherwise arise from

their size.




1 2 3 4


Dark Stars Sun Star Betelgeuse


A. Approximate

radius in miles 430,000 860,000 2,150,000218,000,000

B. Assumed

temperature above

absolute zero. 900 deg. C. 6300 deg. C. 5400 deg. C. 3150 deg. C.

C. Approximate


distance at which

star would cause

solar disturbance

great enough to

cause glaciation


of miles). 1.2 120 220 3200

D. Average

interval between


close enough to

cause glaciation

if all stars 130,000,000,000

were of given [119]

type. Years. 130,000,00038,000,000 700,000


Thus far in our attempt to estimate the distance at which a star might

disturb the sun enough to cause glaciation on the earth, we have

considered only the star's size and temperature. No account has been

taken of the degree to which its atmosphere is disturbed. Yet in the

case of the sun this seems to be one of the most important factors. The

magnetic field of sunspots is sometimes 50 or 100 times as strong as

that of the sun in general. The strength of the magnetic field appears

to depend on the strength of the electrical currents in the solar

atmosphere. But the intensity of the sunspots and, by inference, of the

electrical currents, may depend on the electrical action of Jupiter and

the other planets. If we apply a similar line of reasoning to the stars,

we are at once led to question whether the electrical activity of double

stars may not be enormously greater than that of isolated stars like the


If this line of reasoning is correct, the atmosphere of every double

star must be in a state of commotion vastly greater than that of the

sun's atmosphere even when it is most disturbed. For example, suppose

the sun were accompanied by a companion of equal size at a distance of

one million miles, which would make it much like many known double

stars. Suppose also that in accordance with the general laws of physics

the electrical effect of the two suns upon one another is proportional

to the fourth power of the temperature, the square of the radius, and

the inverse square of the distance. Then the effect of each sun upon the

other would be sixty billion (6 x 10^{10}) times as great as the present

electrical effect of Jupiter upon the sun. Just what this would mean as

to the net effect of a pair of such suns upon the electrical potential

of other bodies at a distance we can only conjecture. The outstanding

fact is that the electrical conditions of a double star must be

radically different and vastly more intense than those of a single star

like the sun.

This conclusion carries weighty consequences. At present twenty or more

stars are known to be located within about 100 trillion miles of the sun

(five parsecs, as the astronomers say), or 16.5 light years. According

to the assumptions employed in Table 5 an average single star would

influence the sun enough to cause glaciation if it came within

approximately 200 billion miles. If the star were double, however, it

might have an electrical capacity enormously greater than that of the

sun. Then it would be able to cause glaciation at a correspondingly

great distance. Today Alpha Centauri, the nearest known star about

twenty-five trillion miles, or 4.3 light years from the sun, and Sirius,

the brightest star in the heavens, is about fifty trillion miles away,

or 8.5 light years. If these stars were single and had a diameter three

times that of the sun, and if they were of the same temperature as has

been assumed for Betelgeuse, which is about fifty times as far away as

Alpha Centauri, the relative effects of the three stars upon the sun

would be, approximately, Betelgeuse 700, Alpha Centauri 250, Sirius 1.

But Alpha Centauri is triple and Sirius double, and both are much hotter

than Betelgeuse. Hence Alpha Centauri and even Sirius may be far more

effective than Betelgeuse.

The two main components of Alpha Centauri are separated by an average

distance of about 2,200,000,000 miles, or somewhat less than that of

Neptune from the sun. A third and far fainter star, one of the faintest

yet measured, revolves around them at a great distance. In mass and

brightness the two main components are about like the sun, and we will

assume that the same is true of their radius. Then, according to the

assumptions made above, their effect in disturbing one another

electrically would be about 10,000 times the total effect of Jupiter

upon the sun, or 2500 times the effect that we have assumed to be

necessary to produce a glacial period. We have already seen in Table 5

that, according to our assumptions, a single star like the sun would

have to approach within 120 billion miles of the solar system, or within

2 per cent of a light year, in order to cause glaciation. By a similar

process of reasoning it appears that if the mutual electrical excitation

of the two main parts of Alpha Centauri, regardless of the third part,

is proportional to the apparent excitation of the sun by Jupiter, Alpha

Centauri would be 5000 times as effective as the sun. In other words, if

it came within 8,500,000,000,000 miles of the sun, or 1.4 light years,

it would so change the electrical conditions as to produce a glacial

epoch. In that case Alpha Centauri is now so near that it introduces a

disturbing effect equal to about one-sixth of the effect needed to cause

glaciation on the earth. Sirius and perhaps others of the nearer and

brighter or larger stars may also create appreciable disturbances in the

electrical condition of the sun's atmosphere, and may have done so to a

much greater degree in the past, or be destined to do so in the future.

Thus an electrical hypothesis of solar disturbances seems to indicate

that the position of the sun in respect to other stars may be a factor

of great importance in determining the earth's climate.


[Footnote 112: H. H. Turner: On a Long Period in Chinese Earthquake

Records; Mon. Not. Royal Astron. Soc., Vol. 79, 1919, pp. 531-539; Vol.

80, 1920, pp. 617-619; Long Period Terms in the Growth of Trees; idem,


[Footnote 113: Harlow Shapley: Note on a Possible Factor in Geologic

Climates; Jour. Geol., Vol. 29, No. 4, May, 1921; Novae and Variable

Stars, Pub. Astron. Soc. Pac., No. 194, Aug., 1921.]

[Footnote 114: J. H. Jeans: Problems of Cosmogony and Stellar Dynamics,

Cambridge, 1919.]

[Footnote 115: This fact is so important and at the same time so

surprising to the layman, that a quotation from The Electron Theory of

Matter by O. W. Richardson, 1914, pp. 326 and 334 is here added.

"It is a very familiar fact that when material bodies are heated they

emit electromagnetic radiations, in the form of thermal, luminous, and

actinic rays, in appreciable quantities. Such an effect is a natural

consequence of the electron and kinetic theories of matter. On the

kinetic theory, temperature is a measure of the violence of the motion

of the ultimate particles; and we have seen that on the electron theory,

electromagnetic radiation is a consequence of their acceleration. The

calculation of this emission from the standpoint of the electron theory

alone is a very complex problem which takes us deeply into the structure

of matter and which has probably not yet been satisfactorily resolved.

Fortunately, we can find out a great deal about these phenomena by the

application of general principles like the conservation of energy and

the second law of thermodynamics without considering special assumptions

about the ultimate constitution of matter. It is to be borne in mind

that the emission under consideration occurs at all temperatures

although it is more marked the higher the temperature.... The energy per

unit volume, in vacuo, of the radiation in equilibrium in an enclosure

at the absolute temperature, T, is equal to a universal constant, A,

multiplied by the fourth power of the absolute temperature. Since the

intensity of the radiation is equal to the energy per unit volume

multiplied by the velocity of light, it follows that the former must

also be proportional to the fourth power of the absolute temperature.

Moreover, if E is the total emission from unit area of a perfectly black

body, we see from p. 330 that E=A'T^{4}, where A' is a new universal

constant. This result is usually known as Stefan's Law. It was suggested

by Stefan in the inaccurate form that the total radiant energy of

emission from bodies varies as the fourth power of the absolute

temperature, as a generalization from the results of experiments. The

credit for showing that it is a consequence of the existence of

radiation pressure combined with the principles of thermodynamics is due

to Bartoli and Boltzmann."]

[Footnote 116: Quoted by Moulton in his Introduction to Astronomy.]

[Footnote 117: Introduction to Astronomy.]

[Footnote 118: The term billions, here and elsewhere, is used in the

American sense, 10^{9}.]

[Footnote 119: The assumed number of stars here is ten times as great as

in the other parts of this line.]