Chapter II: Part 2

Here and there throughout the sky are places where the brighter stars seem to be clustered. These families of stars are of such magnificent proportions as to stagger the imagination. Among the best known are the Pleiades, the Hyades, Coma Berenices and Orion. Although they appear to us very close together, they are not really so, being usually several hundreds of thousands of miles apart. Many of these star-groups are irregular; but numbers of them constitute clusters, which are of various sizes and shapes. Perhaps the most interesting are the so-called “globular clusters,” because they present the appearance of stars having been massed together as globes. Some of them contain five or six thousand stars. Although they appear to us so close together, it has been calculated that, in a cluster containing 5,000 stars the average distance of the stars from one another would be 30,000 times the distance of the sun from the earth! The vast distances of space considered in astronomy may perhaps be realized by this fact--when it is considered that such a cluster appears to us as a single star, only capable of being separated into its component parts by means of high-powered telescopes!

ECLIPSES

The total eclipse of the Sun, January 24, 1925, brought the subject of eclipses to the public attention as never before, and many thousands of persons watched that beautiful and impressive sight through smoked glasses or strips of film.

When we speak of eclipses, we usually mean an eclipse of either the Sun or the Moon. How are such eclipses caused?

A total or partial eclipse of the sun is caused by the moon passing between the earth and the sun, the three celestial bodies forming, as it were, a straight line. The sun is then shut-off from the vision of the inhabitants of our globe over a certain, limited area of its surface. The shadow cast by the moon falls across the earth.

But how is the moon eclipsed? Certainly the sun does not pass between the moon and the earth, on such occasions! What causes the moon to be eclipsed?

The answer is as follows: Inasmuch as both the earth and the moon are illuminated by the sun, they both cast long shadows into space, as any solid body does, when held in front of a strong light. The earth’s shadow trails away for thousands of miles into space. Into this shadow the moon enters, and when it does so, it becomes eclipsed--totally or partially, as the case may be. Total eclipses are instances when the whole surface of the celestial body is apparently covered; partial eclipses are those in which only a portion of the body is dark--the remainder being still visible.

In addition to eclipses, two other astronomical phenomena of interest should here be mentioned: _Transits_, and _Occultations_. By “transit” is meant the passage of some other heavenly body between ourselves and the sun. Thus, Mercury and Venus, both lying nearer the sun than the earth, occasionally pass in front of it. We then have a transit of Venus, or a transit of Mercury, as the case may be.

By “Occultation” is meant the hiding of one heavenly body by another--as when the moon hides some other planet or star, or one planet hides another planet or star. The three bodies are then “in line” as before. Of course, all eclipses represent instances of Occultation.

TELESCOPES

Telescopes are of relatively recent origin; the ancients were forced to make their observations without them, which makes some of their conclusions all the more remarkable. There is considerable evidence that the builders of the Great Pyramid employed the “Grand Gallery” for astronomical observations (see “The Great Pyramid of Egypt,” in the present series), and other devices were employed. But no telescopes of any great power of magnification existed before the last century, while our present marvelous instruments of precision are the evolution of the present century.

Telescopes are of two kinds: refracting and reflecting. Any small telescope exemplifies the former; the incoming light-rays are focussed by a series of lenses, and directly observed by the eye. In the employment of reflecting telescopes, however, another principle is employed: the incoming light-rays are caught and reflected by means of a curved mirror, and focussed on a lens, which in turn is inserted in an elaborate eye-piece, in which the light-rays are magnified and measured. Some of the modern instruments have a forty or more inch aperture, and are capable of enormous powers of magnification.

THE SPECTROSCOPE: SPECTRUM ANALYSIS

For more than two thousand years, astronomy remained a purely mechanical and mathematical science, being limited to observations and deductions therefrom; but in 1860 the method of spectrum-analysis was discovered. This was a most revolutionary discovery, inaugurating, as it did, the whole science of astro-physics; and enabling us to know as much of the physics and chemistry of distant stars and nebulæ--their nature, constitution, and temperature--as we know of the planets of our own system! Even the existence of otherwise invisible stars has been demonstrated in this manner--their orbits, rate of motion, and mass. The science of astro-physics is now one of the most exact in the whole realm of science; and has only been rendered possible by the invention of the spectroscope. As this instrument plays such an important part in all astronomical research, a brief explanation of the instrument becomes necessary.

If a ray of sunlight be passed through a glass prism, the ray is split up into its primary colors; so that, instead of a single spot of white light being visible a narrow band of brilliant colors is seen--ranging from red to violet. But this is not the most important part of the discovery. When this spectrum was closely examined, it was found to be crossed by numerous black bands of various thicknesses. Sometimes these occurred in groups, sometimes singly. By enlarging the spectrum by passing it through several prisms, as many as 3,000 of these bands could be counted. The nature and explanation of these strange bands of blackness remained long uninterpreted, however. It remained for Kirchoff, in 1860, to discover their uses and significance.

Briefly, it is this. The chemical elements, when heated to a state of incandescence, present each one its own characteristic spectrum; each one has its own peculiar markings, or band of lines. No two elements are exactly like in their bands, as shown in the spectrum. Hence, whenever that particular marking is observed, it becomes certain that that element, and none other, is present. These spectra are very varied; iron, for example, has more than 2,000 such bands, while lead and potassium have but one each.

In this way--all the chemical elements having been studied, and their characteristic bands known--it became possible to explore the stars, planets and suns, and discover their chemical composition. For, no matter where an element was discovered--on this earth or on the remotest star--it would always cast its particular spectrum, when thus examined. The effect of all this upon astronomy can be perceived at once. Not only the heavenly bodies known to us, but those which have never been seen by human eye--even when aided by the most powerful telescopes--can be studied and their chemical composition and structure accurately determined. Here is progress indeed!

All this becomes the more remarkable when we stop to consider the immense distances of space, and how widely separated the heavenly bodies are from one another. This may, perhaps, be shown by one or two illustrations. We are, roughly, about 93,000,000 miles from our own sun. Now, the majority of the stars we see are suns, like ours. The sun next removed from us in space is about 275,000 times as far from us as we are from our sun. The orbit of Halley’s comet, of which so much has been written lately, is some 3,280,000,000 miles in length; and this sporadic body, coursing through space at a speed 50 times greater than a rifle bullet, takes 75 years to complete its circuit. The nearest star has been calculated to be nearly 25 trillion miles away; while some of the stars are 40 times as far from us as that!

PHOTOGRAPHY

The second great engine of astronomical research, that has been added during the past century, is _photography_. By this means exact maps may be taken of the heavens at any hour of the night, and the precise position of thousands of stars determined with the utmost exactitude. A chart of the heavens, made in this manner, is not only more complete but more accurate than the combined observations of any number of men could possibly be. Moreover, the photographic plate will record the existence of stars which cannot be seen even with the aid of the most powerful telescopes. This is due to the fact that the plate gradually collects light, and its _cumulative_ effect is noticeable, when its _immediate_ effect cannot be perceived. This power of photographic plates is most valuable, and cannot be duplicated in any other manner. We are assured on good authority that “an ordinary good portrait camera with a lens three or four inches in diameter, if properly mounted so that an exposure of several hours can be made, will show stars so minute that they are invisible even in the great Lick telescope.” An international photographic chart of the heavens is now under way, which, when finished, will represent an accurate catalog of every visible sun, star, and planet, in the sky. After this, any unusual body should be quickly discovered.

But photography is employed not only for mapping out the heavens, but for reaching the farthest stars. The moon and the sun have both been photographed repeatedly, and with most instructive results. The first good pictures of the moon were made by Dr. John W. Draper of New York City, in March, 1840. His son, Dr. Henry Draper, succeeded him in this work, and his photographs were considered the best until Rutherfurd began his remarkable work in 1865. After this, much important work was done in the Lick observatory, and elsewhere. The first picture of the sun was taken in 1845, by Fizeau and Foucault, on a daguerreotype plate. Sun spots, total eclipses, etc., are now studied in great detail by this means.

THE TIDES

Every particle of matter attracts every other particle of matter throughout the entire Universe. The Sun and the Moon both exert a definite pull upon the earth; the moon particularly, being the earth’s satellite, is (so to say) held in place by the earth. The moon, exerting this definite pull, naturally influences the water of the earth most of all, because water is a fluid, mobile body. A heaping-up of the water then occurs--“high tide.” But the moon also attracts the earth to some extent; and the consequence of this is that the water on the opposite side of the globe is, as it were, left behind, which causes a heaping-up of the water there also. Hence, there are two high tides daily, with an interval of 12 hours between them, on opposite sides of the globe.

When the sun and moon pull together, we have the highest tides--“spring tides.” When they do not pull together (being in different parts of the heavens) we have only the surplus pull of the moon over the sun, and the tides are consequently not so high. These are the “neap tides.” All tides act as a sort of check or brake upon the rotation of the earth on its axis--tending to slow down its speed to some extent. “Tidal waves” are due to a combination of special causes.

GRAVITATION

The mysterious influence or “pull” which various celestial bodies exert upon one another is known as gravity or gravitation. We know that masses of matter attract one another according to their size; the larger the body, the greater the force exerted, etc. Further, the influence decreases according to a definite law--according to the square of the distance between the two bodies. The innermost nature of gravitation is still largely a mystery--though various ingenious theories have been advanced in order to explain it. (See my article in “The Monist,” for July, 1913, and pp. 44-46 of “New Discoveries in Science” in the present series.) Gravitation is supposed to act throughout the whole Universe, so that all celestial bodies mutually influence one another, to some extent. Its speed, mode or action, etc., as well as its essence or true nature are, however, unknown even yet; they are still unsolved mysteries!

THE ETHER

At all events, gravitation is thought to act through, or by means of, the Ether--the nature of which is still another mystery! Lodge, in his “Ether of Space,” has given some interesting figures as to the enormous strain which the ether must be supposed to transmit or carry. Lack of space, however, prevents a further discussion of this interesting question; a brief summary may be found on pp. 53-55 of my book on “Chemistry for Beginners,” in the series of Blue Books. For our present purposes, it need only be said that the ether is the only hypothetical connecting-link between celestial bodies--since there is no air or atmosphere in interstellar space. And it is across or by means of this ether that gravitation must be exerted.

ATOMIC ANALOGIES

Recent investigations of the innermost structure of the atom have shown us that it is probably constituted on very much the same plan as our solar system--a central “sun” or proton, round which revolve the negative planets or “electrons.” This question I have treated more fully in my “Chemistry for Beginners,” pp. 42-44, to which the reader is referred.

THUNDER AND LIGHTNING

The lightning flash is merely a huge electric spark, such as may be seen between the terminals of any electric machine. In cases of flashes, or forked lightning, this “spark” is seen directly. Sheet lightning is observed when the original flash is hidden behind clouds, and only its reflection or effects are seen. The rumbling of thunder is due to the reverberations and echoes of the original “peal.” The peal is thought to be due to the sudden rushing together of the molecules of the upper atmosphere, which have been rent asunder by the flash--a sort of vacuum created. Camille Flammarion has written an interesting book on “Thunder and Lightning,” which may be consulted for further details.

FIREBALLS

These are virtually the same as “shooting stars” (_q.v._,) and no essential difference can be pointed to, as to their origin or nature. They are not mere “blobs” of lightning, but solid bodies which sometimes burst, with a great noise--though they are usually noiseless. Many of them appear to be pear-shaped, but they may be seen to change their size and shape during the period of visibility. Fireballs are often accompanied by a train of sparks.

ATMOSPHERIC ELECTRICITY

The surface of the earth is constantly charged with negative electricity of a static character. The upper atmosphere is usually charged positively, though, this may vary according to circumstances. The earth and upper air thus resemble two sheets of tin-foil, with the air an imperfect dialectric between them. This may be broken down, especially in wet or damp weather. The effects upon the mental and physical health are often very noticeable (see Dexter: “Weather Influences,” etc.)

THE EARTH’S MAGNETISM

It has long been known that the magnetic pole does not coincide with the North Pole (or South Pole). The compass points to the magnetic north pole, and not to the true north pole. Lines of magnetic force seem to envelop the earth, terminating at the north and south poles, respectively. Although this is purely a terrestrial phenomenon, it is necessary to mention it here, since it has enabled us to explain, very largely, the remarkable manifestation known as

THE AURORA BOREALIS

This is usually seen in northern climes, and the reason for this is now clear. We know that the corpuscles discharged from a Crookes tube are deflected by a magnet. These corpuscles are discharged in immense numbers by the sun, and rain upon our earth. Now, the earth is a magnet, and these corpuscles are caught by the lines of force girdling our earth, and carried towards the poles, where they find themselves in an atmosphere comparable with high vacua. They then begin to give out the shifting and darting lights characteristic of the cathode rays, causing a certain luminosity. These darting and shifting lights would, on this theory, account for the Aurora Borealis--which is also known to vary with the number of sun-spots.

TIME: MEASUREMENT OF:

Our divisions of time are purely arbitrary, and are all based upon the revolution of our earth upon its axis, which thus constitutes a gigantic clock. All other clocks, watches, etc., are adjusted accordingly. This is really our only way of measuring time; subjective feelings are very illusory, and have to be checked-up by other means. The solar day is the basis of all our calculations--a month, a year, etc., being only so many days in length. Our earth, therefore, is the clock by which we measure the time of the Universe!

SPACE: MEASUREMENT OF:

The measurement of space is always a difficult problem, even for near-by objects (see my “Psychology for Beginners”). When applied to celestial bodies, it becomes immensely complicated, and the only wonder is that such apparently accurate measurements have in fact been made! Such measurements cannot, of course, ever be made _directly_, but must depend upon trigonometry and abstruse mathematical calculations. Most of them are based upon the following principles: If we observe a distant object from two different points-of-view, at a known distance apart, the angle formed by imaginary lines running from the object to one position, and to the other, can readily be calculated. Knowing this angle, much can be ascertained as to the size, distance, etc., of the distant body. If a distant star be viewed from opposite sides of the earth, we have here a known base-line of slightly more than 8,000 miles. But this is altogether too small for astronomical distances! A much longer base-line must be sought. Accordingly, observations are made of a distant star when the earth is (so to say) “north” of the sun, and further observations of the same star when the earth is (so to say) “south” of it--six months later, when the earth has traveled half-way through its orbit round the sun. The diameter of the earth’s orbit being known (186,000,000 miles, almost) we have here a base-line of this size for use in our measurement of the angle and subsequent calculations. Immense as this base-line is, however, it is too small for our purposes, for so immense are astronomical distances, that _no change whatever_ can be observed in the relative positions of certain fixed stars--even when studied from such different positions in space! In other words, the star is so far distant that, when viewed from two positions in space, distant from one another nearly one hundred and eighty-six million miles, it appears to occupy the same position! But a mere summary of this question, and its details would involve an entire volume in itself!

THE INTERNATIONAL DAY LINE

Inasmuch as our earth revolves on its axis, a new day is beginning at some different moment all round the world. This being the case, how are we to fix some definite and official “starting point” for our day--since the day officially begins at midnight, and not at sunrise? To determine this, an arbitrary International Day Line has been drawn, on the 180th meridian--just half way round the globe from Greenwich. Fortunately, this falls in the Pacific Ocean, where there is almost no land. When the sun crosses this line, a new day begins. I have explained this more fully in my book “New Discoveries in Science” in the present series (pp. 40-42).

CALENDARS, ETC.

Our year is a little more than 365 days in length--in fact, nearly 365¼. Because of this fact, an extra day accumulates every four years; and to include this we add this extra day to February every “leap year.” In this way, our celestial bookkeeping is kept fairly accurate. Twelve months of 30 days each would give 360 days, with five days over. It was, however, found that five days was not enough, while five and a quarter was too much. It is interesting to note that Hipparchus, who flourished in the 2nd century B. C., worked on this problem, and fixed 5 days and 55 m., as the time required--a truly remarkable achievement, since it has since been found to be accurate to within less than six minutes.

CURVED SPACE

This, and various other problems connected with the Einstein theories may be found treated in No. 408 of the present series, “An Introduction to Einstein,” by William F. Hudgings.

THE TEMPERATURE OF SPACE

The Earth is warmed by the sun’s rays, some of which are absorbed, while some are reflected. But these rays themselves possess no “heat”; they are merely minute vibrations in the ether. Heat is only present when they strike some solid body. Consequently the vast inter-stellar spaces are tremendously cold--probably at or about absolute zero (-273.10°C). Our earth is not heated directly, as a man is heated by standing in front of a blazing fire; but only by means of electro-magnetic undulations, which traverse millions of miles of space, colder than death, without heating them!

LIGHT IN SPACE

Space is also intensely dark; no light exists there save the faint twinklings of distant stars. The sun illumines our earth, because its rays are reflected from its surface; but space itself is intensely black, just as it is intensely cold It is a “cold world” indeed, once we have stepped off the little planet on which we dwell!

LIFE IN SPACE

All this being so, life in any form cannot very well exist in space--since the conditions for its existence are altogether absent. Arrhenius has, however, suggested, that the “germs of life” might possibly be carried across millions of miles of space on dust particles, propelled by the energy of light. This, however, is a pure theory, which has so far received no official proof.

THE CAUSES OF AN ICE AGE

We know that our Earth has passed through several ice ages, in the past, and various astronomical theories have been advanced in order to explain this fact. Perhaps the most ingenious of these is that advanced by Sir Robert Ball (see his “The Cause of An Ice Age”). Very briefly, it is that the eccentricity of the earth’s orbit and the tilting of the polar axis causes an ice age, or the reverse. If the northern axis is tilted towards the sun, when nearest to it (so to say), then the northern hemisphere will enjoy a genial climate, and if the southern axis be thus tilted, the reverse conditions will prevail. This, and various other theories have, however, been discussed by Finger in his book on “The Ice Age,” in the present series, No. 327.

WHY DO STARS “TWINKLE”?

When we look at a star near the horizon, we at once notice that it twinkles, or “scintillates,” especially in the winter time. The phenomenon is purely atmospheric, and is due to waves of air of unequal density sweeping across the line of sight. When viewed through a telescope, this is sometimes magnified into actual dancing.

WHY DOES THE MOON SOMETIMES APPEAR LARGER?

It is well known that the moon often appears larger when rising or setting--i. e., near the horizon, than when it is overhead. The same is true of the Sun. It is hardly necessary to say that these celestial bodies have not _actually_ increased or decreased in size! Why, then, should we perceive them larger at some times than at others?

The reason for this is two-fold; psychological and optical. In the first place, the Heavens do not appear to us quite round, but somewhat flattened out, like a watch-glass. Hence the moon appears to be much further away when it rises than it does when it is overhead, with nothing between. The moon near the horizon is apparently larger because it seems further away. The second reason is that the refraction of the earth’s atmosphere gives this illusion of increased size.

ARE THE PLANETS INHABITED?

This is a much-disputed point! Various astronomers (Schiaparelli, Lowell, etc.) have contended that they have almost indubitable evidence that Mars is inhabited by living beings like ourselves; other equally competent astronomers assert the contrary. Certainly, none of the planets of our own solar system, with the possible exceptions of Mars and Venus, could possibly be inhabited. That is universally granted. And we have no _direct_ evidence of any other inhabited worlds throughout space. Analogy, however, forces us to believe that, of the millions of suns blazing in the heavens, many of them must be attended by a planetary system such as ours; and if such be the case, there is no reason why life should not originate and thrive thereon as well as upon our own planet. We have, however, no means of proving or disproving this directly.

In our own system, Venus and particularly Mars offer possibilities. Venus probably always turns one face towards the sun, so that this side would be tremendously hot, while the other side would be frozen in perpetual ice. Mars is a possibility; and, as we know, great controversy has raged regarding the habitability of this planet, and as to its “Canals.” The interested reader may refer to Lowell’s “Mars as the Abode of Life,” and “Mars and Its Canals” for the affirmative, and to Maunder’s “Are the Planets Inhabited?” for the negative, side of this question.

A FEW DEFINITIONS

What “Parallax” means. Since the earth revolves round the sun, the stars are apparently in slightly different directions from it at different times of the year. The difference in direction of a star as seen from two points on the earth’s orbit which are separated by the mean distance to the sun is the _parallax_ of the star. In other words, the parallax of a star is the angle subtended by the major semi-axis of the earth’s orbit, as seen from the star.

The “Orbit” of a moving body is its more or less circular passage through space, usually around another larger body, as our earth revolves round the sun. The “eccentricity” of the orbit consists in the fluctuations or variations from its exact path.

The “Ecliptic” System. If we could see the stars near the sun, we should find that the Sun apparently moves eastward among them, completing one revolution in a year. Tracing such a path, it will be found that it more or less coincides with the celestial equator. The equator and the ecliptic intersect at two points; these points are the “equinoxes” the _vernal_ equinox being the one at which the sun crosses the equator from south to north, and the _autumnal_ equinox the other one.

“Satellites.” These are smaller bodies which revolve round large ones, and, so to say, attend them. All except two of the planets are known to have satellites revolving round them, just as they revolve round the sun. Mercury and Venus have none; the earth has the moon; Mars has two little moons, only a few miles in diameter; Jupiter has four large satellites and four small ones; Saturn has ten, one of which is larger than Mercury; Uranus has four satellites, and Neptune one.

The “Planetoids.” Between Mars and Jupiter a number of small bodies have been discovered, moving in a regular orbit; these have been called planetoids. If some planet has once occupied this mid-way position, and subsequently exploded, the fragments would occupy the position occupied by the planetoids. Whether or not this is their origin is a disputed point, which it would take us too far afield to consider here. They suggest the possibility.

“Planets.” These are the bodies revolving round a central sun. Aside from those constituting our own solar system, we see no planets in space; we see suns, or stars; but if the latter have planets attendant upon them, we cannot see them.

The point of the moon’s orbit nearest the earth is called the _perigee_; the furthest point, the _apogee_.

TRANSCRIBER’S NOTES

Author’s spelling of “dialectric” has been retained.

Inconsistencies in hyphenation have been left unchanged.

Typos corrected:

Title page: missing opening quote in “Psychology for Beginners”

Page 13: “concenses” to “consensus”

Page 17: “equitorial” to “equatorial”, "Myriads" to "myriads" (lowercase)

Page 49: “on my book” to “of my book”

Page 54: “litle” to “little”

Page 59: “Unanus” to “Uranus”