I presume that, in the termination of my last sentence, few of my readers have noticed anything especially objectionable — particularly wrong. I said that the distance of the Earth from the Sun being taken at one foot, the distance of Neptune would be forty feet, and that of Alpha Lyrae one hundred and fifty-nine. The proportion between one foot and one hundred and fifty-nine has appeared, perhaps, to convey a sufficiently definite impression of the proportion between the two intervals — that of the Earth from the Sun, and that of Alpha Lyrae from the same luminary. But my account of the matter should, in reality, have run thus:— The distance of the Earth from the Sun being taken at one foot, the distance of Neptune would be forty feet, and that of Alpha Lyrae one hundred and fifty-nine — miles; that is to say, I had assigned to Alpha Lyrae, in my first statement of the case, only the 5280th part of that distance which is the least distance possible at which it can actually lie.
To proceed:— However distant a mere planet is, yet when we look at it through a telescope we see it under a certain form — of a certain appreciable size. Now I have already hinted at the probable bulk of many of the stars; nevertheless, when we view any one of them, even through the most powerful telescope, it is found to present us with no form, and consequently with no magnitude whatever. We see it as a point and nothing more.
Again; — Let us suppose ourselves walking, at night, on a highway. In a field on one side of the road, is a line of tall objects, say trees, the figures of which are distinctly defined against the background of the sky. This line of objects extends at right angles to the road, and from the road to the horizon. Now, as we proceed along the road, we see these objects changing their positions, respectively, in relation to a certain fixed point in that portion of the firmament which forms the background of the view. Let us suppose this fixed point — sufficiently fixed for our purpose — to be the rising moon. We become aware, at once, that while the tree nearest us so far alters its position, in respect to the moon, as to seem flying behind us, the tree in the extreme distance has scarcely changed at all its relative position with the satellite. We then go on to perceive that the farther the objects are from us, the less they alter their positions; and the converse. Then we begin, unwittingly, to estimate the distances of individual trees by the degrees in which they evince the relative alteration. Finally, we come to understand how it might be possible to ascertain the actual distance of any given tree in the line by using the amount of relative alteration as a basis in a simple geometrical problem. Now, this relative alteration is what we call “parallax;” and by parallax we calculate the distances of the heavenly bodies. Applying the principle to the trees in question, we should, of course, be very much at a loss to comprehend the distance of that tree, which, however far we proceeded along the road, should evince no parallax at all. This, in the case described, is a thing impossible; but impossible only because all distances on our Earth are trivial indeed; in comparison with the vast cosmical quantities, we may speak of them as absolutely nothing.
Now, let us suppose the star Alpha Lyrae directly overhead; and let us imagine that, instead of standing on the Earth, we stand at one end of a straight road stretching through Space to a distance equalling the diameter of the Earth’s orbit — that is to say, to a distance of one hundred and ninety millions of miles. Having observed, by means of the most delicate micrometrical instruments, the exact position of the star, let us now pass along this inconceivable road, until we reach its other extremity. Now, once again, let us look at the star. It is precisely where we left it. Our instruments, however delicate, assure us that its relative position is absolutely — is identically the same, as at the commencement of our unutterable journey. No parallax — none whatever — has been found.
The fact is, that, in regard to the distance of the fixed stars — of any one of the myriads of suns glistening on the farther side of that awful chasm which separates our system from its brothers in the cluster to which it belongs — astronomical science, until very lately, could speak only with a negative certainty. Assuming the brightest as the nearest, we could say, even of them, only that there is a certain incomprehensible distance on the hither side of which they cannot be; how far they are beyond it we had in no case been able to ascertain. We perceived, for example, that Alpha Lyrae cannot be nearer to us than nineteen trillions, two hundred billions of miles; but, for all we knew, and indeed for all we now know, it may be distant from us the square, or the cube, or any other power of the number mentioned. By dint, however, of wonderfully minute and cautious observations, continued, with novel instruments, for many laborious years, Bessel, not long ago deceased, has lately succeeded in determining the distance of six or seven stars; among others, that of the star numbered 61 in the constellation of the Swan. The distance in this latter instance ascertained, is six hundred and seventy thousand times that of the Sun; which last, it will be remembered, is ninety-five millions of miles. The star 61 Cygni, then, is nearly sixty-four trillions of miles from us — or more than three times the distance assigned, as the least possible, for Alpha Lyrae.
In attempting to appreciate this interval by the aid of any considerations of velocity, as we did in endeavoring to estimate the distance of the Moon, we must leave out of sight, altogether, such nothings as the speed of a cannon ball, or of sound. Light, however, according to the latest calculations of Struve, proceeds at the rate of one hundred and sixty-seven thousand miles in a second. Thought itself cannot pass through this interval more speedily — if, indeed, thought can traverse it at all. Yet, in coming from 61 Cygni to us, even at this inconceivable rate, light occupies more than ten years; and, consequently, were the star this moment blotted out from the Universe, still, for ten years, would it continue to sparkle on, undimmed in its paradoxical glory.
Keeping now in mind whatever feeble conception we may have attained of the interval between our Sun and 61 Cygni, let us remember that this interval, however unutterably vast, we are permitted to consider as but the average interval among the countless host of stars composing that cluster, or “nebula,” to which our system, as well as that of 61 Cygni, belongs. I have, in fact, stated the case with great moderation; — we have excellent reason for believing 61 Cygni to be one of the nearest stars, and thus for concluding, at least for the present, that its distance from us is less than the average distance between star and star in the magnificent cluster of the Milky Way.
And here, once again and finally, it seems proper to suggest that even as yet we have been speaking of trifles. Ceasing to wonder at the space between star and star in our own or in any particular cluster, let us rather turn our thoughts to the intervals between cluster and cluster, in the all comprehensive cluster of the Universe.
I have already said that light proceeds at the rate of one hundred and sixty-seven thousand miles in a second — that is, about ten millions of miles in a minute, or about six hundred millions of miles in an hour; yet so far removed from us are some of the “nebulae” that even light, speeding with this velocity, could not and does not reach us, from those mysterious regions, in less than three millions of years. This calculation, moreover, is made by the elder Herschel, and in reference merely to those comparatively proximate clusters within the scope of his own telescope. There are “nebulae,” however, which, through the magical tube of Lord Rosse, are this instant whispering in our ears the secrets of a million of ages bygone. In a word, the events which we behold now — at this moment — in those worlds — are the identical events which interested their inhabitants ten hundred thousand centuries ago. In intervals, in distances, such as this suggestion forces upon the soul rather than upon the mind, we find, at length, a fitting climax to all hitherto frivolous considerations of quantity.
Our fancies thus occupied with the cosmical distances, let us take the opportunity of referring to the difficulty which we have so often experienced, while pursuing the beaten path of astronomical reflection, in accounting for the immeasurable voids alluded to; in comprehending why chasms so totally unoccupied and therefore apparently so needless, have been made to intervene between star and star, between cluster and cluster; in understanding, to be brief, a sufficient reason for the Titanic scale, in respect of mere Space, on which the
