Part 14

That one star differs from another star in glory we have long heard, but our knowledge of physical things depends largely on our ability to answer the question, “how much?” and the value of this new work lies in the accuracy and fulness of its measures; for in this case the whole heavens visible from Cambridge to near the southern horizon have been surveyed, and the brightness of every naked-eye star repeatedly measured, so that all future changes can be noted. This great work has taxed the resources of a great observatory, and its results are only to be adequately valued by other astronomers; but Professor Pickering’s own investigations on variable stars have a more popular interest. It is surely an amazing fact that suns as large or larger than our own should seem to dwindle almost to extinction, and regain their light within a few days or even hours; yet the fact has long been known, while the cause has remained a mystery. A mystery, in most cases, it remains still; but in some we have begun to get knowledge, as in the well-known instance of Algol, the star in the head of Medusa. Here it has always been thought probable that the change was due to something coming between us and the star; but it is on this very account that the new investigation is more interesting, as showing how much can be done on an old subject by fresh reasoning alone, and how much valuable ore may lie in material which has already been sifted. The discussion of the subject by Professor Pickering, apart from its elevated aim, has if, in its acute analysis only, the interest belonging to a story where the reader first sees a number of possible clews to some mystery, and then the gradual setting aside, one by one, of those which are only loose ends, and the recognition of the real ones which lead to the successful solution. The skill of the novelist, however, is more apparent than real, since the riddle he solves for us is one he has himself constructed, while here the enigma is of Nature’s propounding; and if the solution alone were given us, the means by which it is reached would indeed seem to be inexplicable.

This is especially so when we remember what a point there is to work on, for the whole system reasoned about, though it may be larger than our own, is at such a distance that it appears, literally and exactly, far smaller to the eye than the point of the finest sewing-needle; and it is a course of accurate reasoning, and reasoning alone, on the character of the observed changing brightness of this point, which has not only shown the existence of some great dark satellite, but indicated its size, its distance from its sun, its time of revolution, the inclination of its orbit, and still more. The existence of dark invisible bodies in space, then, is in one case at least demonstrated, and in this instance the dark body is of enormous size; for, to illustrate by our own solar system, we should probably have to represent it in imagination by a planet or swarm of planetoids hundreds of times the size of Jupiter, and (it may be added) whirling around the sun at less than a tenth the distance of Mercury.

Of a wholly different class of variables are those which have till lately only been known at intervals of centuries, like that new star Tycho saw in 1572. I infer from numerous inquiries that there is such a prevalent popular notion that the “Star of Bethlehem” may be expected to show itself again at about the present time, that perhaps I may be excused for answering these questions in the present connection.

In the first place, the idea is not a new, but a very old one, going back to the time of Tycho himself, who disputed the alleged identity of his star with that which appeared to the shepherds at the Nativity. The evidence relied on is, that bright stars are said to have appeared in this constellation repeatedly at intervals of from three hundred and eight to three hundred and nineteen years (though even this is uncertain); and as the mean of these numbers is about three hundred and fourteen, which again is about one-fifth of 1572 (the then number of years from the birth of Christ), it has been suggested, in support of the old notion, that the Star of Bethlehem might have been a variable, shining out every three hundred and fourteen or three hundred and fifteen years, whose fifth return would fall in with the appearance that Tycho saw, and whose _sixth_ return would come in 1886 or 1887. This is all there is about it, and there is nothing like evidence, either that this was the star seen by the Wise Men, or that it is to be seen again by us. On the other hand, nothing in our knowledge, or rather in our ignorance, authorizes us to say positively it cannot come again; and it may be stated for the benefit of those who like to believe in its speedy return, that if it does come, it will make its appearance some night in the northern constellation of Cassiopeia’s chair, the position originally determined by Tycho at its last appearance, being twenty-eight degrees and thirteen minutes from the pole, and twenty-six minutes in right ascension.

We were speaking of these new stars as having till lately only appeared at intervals of centuries; but it is not to be inferred that if they now appear oftener it is because there are more of them. The reason is, that there are more persons looking for them; and the fact is recognized that, if we have observers enough and look closely enough, the appearance of “new stars” is not so very rare a phenomenon. Every one at all interested in such matters remembers that in 1866 a new star broke out in the Northern Crown so suddenly that it was shining as bright as the Polar Star, where six hours before there had been nothing visible to the eve. Now all stars are not as large as our sun, though some are much larger; but there are circumstances which make it improbable that this was a small or near object, and it is well remembered how the spectroscope showed the presence of abnormal amounts of incandescent hydrogen, the material which is perhaps the most widely diffused in the universe (and which is plentiful, too, in our own bodies), so that there was some countenance to the popular notion that this was a world in flames. We were, at any rate, witnessing a catastrophe which no earthly experience can give us a notion of, in a field of action so remote that the flash of light which brought the news was unknown years on the way, so that all this--strange but now familiar thought--occurred long before we _saw_ it happen. The star faded in a few days to invisibility to the naked eye, though not to the telescope; and, in fact, all these phenomena at present appear rather to be enormous and sudden enlargements of the light of existing bodies than the creation of absolutely new ones; while of these “new stars” the examples may almost be said to be now growing numerous, two having appeared in the last two years.

Not to enlarge, then, on this chapter of photometry, let us add, in reference to another department of stellar astronomical work, that the recognized master in the study of double stars the world over is not an astronomer by profession, at the head of some national observatory in Berlin or Paris, but a stenographer in the Chicago law-courts, Mr. W. S. Burnham, who, after his day’s duties, by nightly labor, prolonged for years with the small means at an amateur’s command, has perhaps added more to our knowledge of his special subject in ten years than all other living astronomers.

We have here only alluded to the spectroscope in its application to stellar research, and we cannot now do more than to note the mere headlines of the chapters that should be written on it.

First, there is the memorable fact that, after reaching across the immeasurable distances, we find that the stars are like _us_,--like in their ultimate elements to those found in our own sun, our own earth, our own bodies. Any fuller view of the subject than that which we here only indicate, would begin with the evidence of this truth, which is perhaps on the whole the most momentous our science has brought us, and with which no familiarity should lessen our wonder, or our sense of its deep and permanent significance.

Next, perhaps, we should understand that, invading the province of the Old Astronomy, the spectroscope now tells us of the motions of these stars, which we cannot see move,--motions in what we have always called the “fixed” stars, to signify a state of fixity to the human eye, which is such, that to it at the close of the nineteenth century they remain in the same relative positions that they occupied when that eye first looked on them, in some period long before the count of centuries began.

In perhaps the earliest and most enduring work of man’s hands, the great pyramid of Egypt, is a long straight shaft, cut slopingly through the solid stone, and pointing, like a telescope, to the heavens near the pole. If we look through it now we see--nothing; but when it was set up it pointed to a particular star which is no longer there. That pyramid was built when the savages of Britain saw the Southern Cross at night; and the same slow change in the direction of the earth’s axis, that in thousands of years has borne that constellation to southern skies, has carried the stone tube away from the star that it once pointed at. The actual motion of the star itself, relatively to our system, is slower yet,--so inconceivably slow that we can hardly realize it by comparison with the duration of the longest periods of human history. The stone tube was pointed at the star by the old Egyptians, but “Egypt itself is now become the land of obliviousness, and doteth. Her ancient civility is gone, and her glory hath vanished as a phantasma. She poreth not upon the heavens, astronomy is dead unto her, and knowledge maketh other cycles. Canopus is afar off, Memnon resoundeth not to the Sun, and Nilus heareth strange voices.” In all this lapse of ages, the star’s own motion could not have so much as carried it across the mouth of the narrow tube. Yet a motion to or from us of this degree, so slow that the unaided eve could not see it in thousands of years of watching, the spectroscope, first efficiently in the hands of the English astronomer, Dr. Huggins, and later in those of Professor Young of Princeton, not only reveals at a look, but tells us the amount and direction of it, in a way that is as strange and unexpected, in the view of our knowledge a generation ago, as its revelation of the essential composition of the bodies themselves.

Again, in showing us this composition, it has also shown us more, for it has enabled us to form a conjecture as to the relative ages of the stars and suns; and this work of classifying them, not only according to their brightness, but each after his kind, we may observe was begun by a countryman of our own, Mr. Rutherfurd, who seems to have been among the first after Fraunhofer to apply the newly-invented instrument to the stars, and quite the first to recognize that these were, broadly speaking, divisible into a few leading types, depending not on their size but on their essential nature. After him Secchi (to whom the first conception is often wrongly attributed) developed it, and gave four main classes into which the stars are in this way divisible, a classification which has been much extended by others; while the first carefully delineated spectra were those of Dr. Huggins, who has done so much for all departments of our science that in a fuller account his name would reappear in every chapter of this New Astronomy, and than whom there is no more eminent living example of its study. Owing to their feeble light, years were needed when he began his work to depict completely so full a single spectrum as that he gives of Aldebaran, though he has lived to see stellar spectrum photography, whose use he first made familiar, producing in its newest development, which we give here, the same result in almost as many minutes. Before we present this latest achievement of celestial photography, let us employ the old method of an engraving made from eye-drawings, once more, to illustrate on page 222 the distinct character of these spectra, and their meaning. In the telespectroscope, the star is drawn out into a band of colored light, but here we note only in black and white the lines which are seen crossing it, the red end in these drawings being at the left, and the violet at the right; and we may observe of this illustration, that though it may be criticised by the professional student, and though it lack to the general reader the attraction of color, or of beautiful form, it is yet full of interest to any one who wishes to learn the meaning of the message the star’s light can be made to yield through the spectroscope, and to know how significant the differences are it indicates between one star and another, where all look so alike to the eye. First is the spectrum of a typical white or blue-white star, Sirius,--the very brightest star in the sky, and which we all know. The brighter part of the spectrum is a nearly continuous ribbon of color, crossed by conspicuous, broad, dark lines, exactly corresponding in place to narrower ones in our sun, and due principally to hydrogen. Iron and magnesium are also indicated in this class, but by too fine lines to be here shown.

Sirius, as will be presently seen, belongs to the division of stars whose spectrum indicates a very high temperature, and in this case, as in what follows, we may remark (to use in part Mr. Lockyer’s words) that one of the most important distinctions between the stars in the heavens is one not depending upon their mass or upon anything of that kind, but upon conditions which make their spectra differ, just in the way that in our laboratories the spectrum of one and the same body will differ at different temperatures.

What these absolutely are in the case of the stars, we may not know; but placing them in their most probable relative order, we have taken as an instance of the second class, or lower-temperature stage, our own sun. The impossibility of giving a just notion of its real complexity may be understood, when we state that in the recent magnificent photographs by Professor Rowland, a part alone of this spectrum occupies something like fifty times the space here given to the whole, so that, crowded with lines as this appears, scarcely one in fifty of those actually visible can be given in it. Without trying to understand all these now, let us notice only the identity of two or three of its principal elements with those found in other stars, as shown by the corresponding identity of some leading lines. Thus, C and F (with others) are known to be caused by hydrogen; D, by sodium; _b_, by magnesium; while fainter lines are given by iron and by other substances. These elements can be traced by their lines in most of the different star-spectra on this plate, and all those named are constituents of our own frames.

The hydrogen lines are not quite accurately shown in the plate from which our engraving is made, those in Sirius, for instance, being really wider by comparison than they are here given; and we may observe in this connection, that by the particular appearance such lines wear in the spectrum itself we can obtain some notion of the _mass_ of a star, as well as of its chemical constitution. We can compare the essential characteristics of such bodies, then, without reference to their apparent size, or as though they were all equally remote; and it is a striking thought, that when we thus rise to an impartial contemplation of the whole stellar universe, our sun, whose least ray makes the whole host of stars disappear, is found to be not only itself a star, but by comparison a small one,--one at least which is more probably below than above the average individual of its class, while some, such as Sirius, are not impossibly hundreds of times its size.

Then comes a third class, such as is shown in the spectrum of the brightest star in Orion, looking still a little like that of our sun; but yet more distinctively in that of the brightest star in Hercules, looking like a columnar or fluted structure, and concerning which the observations of Lockyer and others create the strong presumption, not to say certainty, that we have here a lower temperature still. Antares and other reddish stars belong to this division, which in the very red stars passes into the fourth type, and there are more classes and subclasses without end; but we invite here attention particularly to the first three, much as we might present a child, an adult, and an old man, as types of the stages of human existence, without meaning to deny that there are any number of ages between. We can even say that this may be something more than a mere figure of speech, and that a succession in age is not improbably pointed at in these types.

We may have considered--perhaps not without a sort of awe at the vastness of the retrospect--the past life of the worlds of our own system, from our own globe of fluid fire as we see it by analogy in the past, through the stages of planetary life to the actual condition of our present green earth, and on to the stillness of the moon. Yet the life history of our sun, we can hardly but admit, is indefinitely longer than this. We feel, rather than comprehend, the vastness of the period that separates our civilization from the early life of the world; but what is this to the age of the sun, which has looked on and seen its planetary children grow? Yet if we admit this temperature classification of the stars, we are not far from admitting that the spectroscope is now pointing out the stages in the life of suns themselves; suns just beginning their life of almost infinite years; suns in the middle of their course; suns which are growing old and casting feebler beams,--all these and many more it brings before us.

Another division of our subject would, with more space, include a fuller account of that strange and most interesting development of photography which is going on even while we write; and this is so new and so important, that we must try to give some hint of it even in this brief summary, for even since the first numbers of this series were written, great advances have taken place in its application to celestial objects.

Most of us have vague ideas about small portions of time; so much so, that it is rather surprising to find to how many intelligent people, a second, as seen on the clock face, is its least conceivable interval. Yet a second has not only a beginning, middle, and end, as much as a year has, but can, in thought at least, be divided into just as many numbered parts as a year can. Without entering on a disquisition about this, let us try to show by some familiar thing that we can at any rate not only divide a second in imagination into, let us say, a hundred parts, but that we can observe distinctly what is happening in such a short time, and make a picture of it,--a picture which shall be begun and completed while this hundredth of a second lasts.

Every one has fallen through at least some such a little distance as comes in jumping from a chair to the floor, and most of us, it is safe to say, have a familiar impression of the fact that it takes, at any rate, less than a second in such a case from the time the foot leaves its first support till it touches the ground. Plainly, however large or small the fall may be, each fraction of an inch of it must be passed through in succession, and if we suppose the space to be divided, for instance, into a hundred parts, we must divide in thought the second into at least as many, since each little successive space was traversed in its own little interval of time, and the whole together did not make a second. We can even, as a matter of fact, very easily calculate the time that it will take anything which has already fallen, let us say one foot, to fall an inch more; and we find this, in the supposed instance, to be almost exactly one one-hundredth of a second. On page 243 is a reproduction of a photograph from Nature, of a man falling freely through the air. He has dropped from the grasp of the man above him, and has already fallen through some small distance,--a foot or so. If we suppose it to be a foot, since we can see that the man’s features are not blurred, as they would undoubtedly have been had he moved even much less than an inch while this picture was being taken, it follows, from what has been said, that the making of the whole picture--landscape, spectators, and all--occupied not _over_ one one-hundredth of a second.

We have given this view of “the falling man” because, rightly understood, it thus carries internal evidence of the limit of time in which it could have been made; and this will serve as an introduction to another picture, where probably no one will dispute that the time was still shorter, but where we cannot give the same kind of evidence of the fact.

“Quick as lightning” is our common simile for anything occupying, to ordinary sense, no time at all. Exact measurements show that the electric spark does occupy a time, which is almost inconceivably small, and of which we can only say here that the one one-hundredth of a second we have just been considering is a long period by comparison with the duration of the brightest portion of the light.

On page 245 we have the photograph of a flash of lightning (which proves to be several simultaneous flashes), taken last July from a point on the Connecticut coast, and showing not only the vivid zigzag streaks of the lightning itself, but something of the distant sea view, and the masts of the coast survey schooner “Palinurus” in the foreground, relieved against the sky. We are here concerned with this interesting autograph of the lightning, only as an illustration of our subject, and as proving the almost infinite sensitiveness of the recent photographic processes; for there seems to be no limit to the briefness of time in which, these can so act in some degree, whether the light be bright or faint, and no known limit to the briefness of time required for them to act _effectively_ if the light be bright enough.