Part 3

It has been shown that our whole solar system is sweeping through space at the speed of about ten miles a second towards the stars in the constellation Hercules, and particularly towards Vega, one of its suns. However, Vega is likewise moving through space, so that by the time our sun reaches the spot now occupied by Vega (half a million years or so) Vega will no longer occupy that position, and no “collision” will take place in consequence! We shall not, in fact, pass very near that star.

DISTANCES OF THE STARS

Astronomical distances are so vast that they can only be measured in the mind relatively. The distances between the planets in our own solar system seem big enough; yet they shrink into insignificance when compared to the distances which separate our whole solar system from even the nearest of the stars. _Alpha Centauri_ is the nearest star, and it is separated from us by a distance 276,000 times as great as that which separates us from our sun. It is approximately 25 billion miles away. Traveling with the speed of an express train flung into space, at 40 miles an hour, towards the nearest star, without any stoppage or any slowing down, we should not arrive at our destination until after an interrupted flight of 75 million years. Yet this is our nearest neighbour! Only a _very few_ of the stars are within 400,000,000,000,000 miles of the sun. The great majority of them are many times this distance from us.

So vast are these distances that some simple means of expressing them on paper was sought. A “light Year” was finally decided upon as the _unit_ of measurement--that is, the distance which light would travel in one year, speeding at the rate of 186,000 miles a second. It has been estimated that many stars are one, two, three and perhaps five hundred thousand light-years distant from us in space. The interested reader may figure-out the number of miles this represents for himself!

TEMPERATURE OF THE STARS

Measurements which have been undertaken prove that the surface temperature of our Sun is between 5,000°C. and 7,000°C. It is thought that many stars are considerably hotter than this. We can form no adequate conception of such intense heat; all matter would be vaporized; yet, under the enormous pressures which must prevail, these vapors would in turn be converted into thick, semi-fluid substances--especially in the interior.

FIXED STARS

The so-called “fixed” stars are those which do not appear to change their positions in the heavens for long periods of time together. There are, of course, no “fixed” stars at all since every celestial body is moving with greater or lesser rapidity through space; but these stars are so far distant from us that such movements are inappreciable, even after long periods of time, and in spite of the most careful observations. In comparison with the more rapidly moving heavenly bodies, they do not appear to “move,” and have been denominated “fixed stars” in consequence.

DOUBLE STARS

A large number of stars appear single, when viewed by the naked eye, but when seen through a powerful telescope, are seen to be, in reality, two stars which revolve round one another. Many thousands of such double stars are now known to exist; indeed, apparently single stars have been found, upon closer examination, to be composed of a group of four or five or more stars--so that the name “multiple stars” has been given to such groups. They are near one another in the astronomical use of that word--though they may actually be hundreds of thousands, or millions of miles apart. Many of these double stars seem to be quite separate from one another. Others appear to have some physical connection. Those which are known to form systems are known as _binaries_.

COLORED STARS

Many of the double stars exhibit curious and beautiful phenomena of complementary colors. In such cases, the larger star is usually more or less reddish or orange, and the smaller one bluish-green or greenish-blue. Many of the double stars, on the contrary, are of the same color. There are white, red, blue, orange, green and yellow stars. The planets also vary greatly in color--Venus, e.g., being white, Mars reddish, etc. Inasmuch as the planets only reflect light, however, this is due to quite different causes; the other colored stars are self-luminous suns which emit light of their own.

VARIABLE STARS

In addition to variations in the color of stars, they also vary greatly in brilliance, and certain stars are much brighter at times than at others. In some cases these changes in brilliance are regular; in others, irregular. “Omicron,” for example, which, Bayer recorded in his Atlas in 1603, is a regular variable; its period of change is 331 days, 8 hours; in other words, it reaches its greatest brightness about 12 times in 11 years, when it sometimes attains the brilliancy of a star of the 2nd magnitude, at which brilliancy it remains stationary for about a fortnight. It then diminishes during about three months, until it sinks down to a star of magnitude 9½, or even becomes totally invisible. It remains in this condition for about 5 months, and then gradually recovers--during the next following 3 months--its maximum brilliancy. In other words, its brilliancy is absolutely periodic. Other variables are by no means regular, however, but “come and go” at different intervals.

Various theories have been advanced by way of explanation--one of the simplest being that such stars are in reality double, one being luminous and the other not; and that, during their revolutions, the non-luminous star partially or totally eclipses the bright one, at stated intervals. The whole subject, however, is difficult, and much yet remains to be learned concerning these variable stars.

TEMPORARY STARS

From time to time, stars have suddenly appeared in the heavens, where no star existed before! Such stars have usually become increasingly brilliant for a short period of time, and then as suddenly died away again, leaving no trace of their existence behind them. These “new stars” for long puzzled astronomers. The theory often advanced to explain them is that some distant star has “exploded,” and the increasing brilliance which we see is the result. If such were the case, its sudden dimming-down and disappearance would be quite intelligible--as would be its sudden appearance. A large number of such stars have now been recorded, and their existence is no longer in doubt. In some cases, they have remained visible for weeks or months before their final disappearance.

STAR GROUPS--CLUSTERS

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: