God's glory in the heavens/Stellar Grouping
Lord Rosse's Great Telescope.
XV.
STELLAR GROUPING.
At the same time that recent observation has dispelled the nebulous matter, from which worlds were supposed to be formed, it has opened up wondrous views of sidereal grouping. The telescope of Lord Rosse has converted the atoms of nebulous matter into suns, and instead of molecular condensation, we must deal with stellar aggregation. The nebulæ which were indicated, as shewing progressive condensation, are still available for the same obiect; the condensation being cosmical not atomic. But this leads us to the wider question of the distribution of stars throughout space.
Stellar distribution may be compared to the distribution of human habitations on the face of the earth. These habitations, instead of being equally distributed, are grouped into towns and cities, with suburban mansions and villas. Again, a more general classification is afforded by their distribution into different kingdoms, often separated from one another by great natural boundaries.
A similar grouping is observable in the celestial bodies. The first step of aggregation is exemplified in the case of double stars. It was found that the number of twin stars was much greater than what could be accounted for by chance distribution; and it was therefore suspected that there was some physical bond of connexion. This surmise has been fully borne out by observation. Many have been found to revolve round the same centre, and several have completed their period since the first observations. Systems, however, are found in the heavens with every gradation, from twin stars up to clusters, whose constituent elements cannot be numbered. These clusters, too, are often evidently connected with a higher grade of grouping—bearing the same relation to the whole system, that a single square of a city bears to the city itself.
The aggregation of stars to which our system is believed to belong, is that of the Milky Way—that faint zone of light seen on a clear night circling the heavens. The Milky Way or galaxy is believed to be a stratum of stars in which our system is embedded I as a constituent element—the thickness of the stratum being small compared to its other dimensions. If the eye of the observer be situated near the centre of the stratum, the greatest number will be seen in the direction of the circumference; and these are so numerous, that their intermingling rays produce the impression of a zone of light. On looking towards either side of the stratum comparatively few stars will be seen. A section of the Milky Way may be compared to a long narrow belt of trees. The eye, situated in the middle of such belt, would, on looking: along the length, see all the trunks of the trees blending in one mass without seeing through. On looking, however, to either side, there would be few seen, and these quite separated from one another. All the stars visible to the naked eye, as well as those constituting the galaxy, are believed to belong to the same system. There is good reason for supposing that the stars do not vary much from a certain average size, consequently those which appear largest are nearest us. The stratum of which our firmament consists, is cleft into two branches. This is shewn by the zone of light dividing itself, for a considerable part of its course, into two pathways across the heavens. The division of the galaxy is shewn in the following section, in which S is the position of the sun. The
Milky Way, when carefully examined, exhibits a mottled appearance, shewing an unequal distribution of stars. Some spots appear absolutely black, and one very marked is, from this circumstance, called the coal-sack; some look like holes or rather prolonged funnels, projecting beyond the general limits of the stratum. An idea may be formed of the crowding of the stars in the Milky Way from the fact, that in many places upwards of a thousand stars have been counted in a space which the disc of the moon would cover. Probably the whole number amounts to more than twenty millions.
But the Milky Way, with its outlying stars constituting our firmament, is only one of the many thousands of the stellar aggregations scattered throughout space. These are the nebulæ which, when resolved by adequate optical power, yield galaxies, wondrous from their dimensions and the strangeness of their forms. There are some nebulous masses quite visible to the naked eye. The most remarkable of these are the clouds of Magellan in the southern hemisphere. They are very conspicuous, and occupy Plate VIII
CONCENTRIC NEBULÆ
Plate XI.
1. DUMB BELL NEBULA. 2.PERFORATED NEBULA.
a considerable apparent space in the heavens. One of them is so bright, that the full moon does not obliterate it. They are very similar in structure to our galaxy; but there are innumerable nebulae embedded in the midst of them. The most common form is the spherical, but this shape is often due to the defect of optical power. What appears a perfect sphere with a small telescope, will often assume a most irregular figure under a larger power—the fainter portions not being discernible in the feebler instrument. We have, thus, ring nebulae, the crab nebula, the dumb-bell nebula, and various forms of spiral nebulae. The revelation of the spiral structure is due to the powerful telescopes of LordEosse; and the most interesting circumstance is, that this appears to be a very general character of the constitution of nebula. Our figure only illustrates the simpler form of the spiral, but, sometimes, eight or nine originate from one centre; and nebulae, hitherto supposed to be planetary, or presenting a uniform disc, are now resolved into an aggregate of many spirals, curiously combined.
Another curious feature has been discovered, very similar, apparently, to stratification. In the midst of the nebula long parallel bands are seen running along the whole length; these bands are perfectly black. The great nebula of Andromeda is a good illustration.
The recent revelations of the telescope have presented conditions and forms of forces to the astounded gaze of the astronomer, hitherto altogether unknown in celestial mechanics. It is impossible to view the strange figures of the nebulae without being persuaded that they indicate action, vitality, progress. We cannot survey the many forms which the clouds in our atmosphere assume, without being persuaded that they are the result of forces determining their peculiar configuration. The nebulæ, in like manner, speak of mighty forces moulding them into their particular form and constitution. The nebular hypothesis contemplates particles of matter sweeping round into a vortex and forming a solid body; but the astronomer, on the other hand, has now to contemplate streams of bright suns hastening on along their spiral course to some unknown destiny. The idea of effort is written upon these strange forms—effort to reach some more perfect ultimate form. Sir John Herschel threw out a conjecture as to the manner in which the great condensation observable in some nebula may have been produced. He imagines that the motions of the stars might be destroyed, to some extent, by collisions, which would have the effect of making them revolve round the common centre of gravity in a narrower circle; just as the earth would contract its orbit, should part of its velocity be destroyed by a collision with a comet. The effect of such collision would be, to produce great apparent condensation in the group of stars. This great condensation, with a faint surrounding nebulosity, was one of the strongholds of the nebular hypothesis, as it was thought highly improbable that the central condensation should arise merely from the grouping of stars.
As individual stars are not scattered equally throughout space, so the groups which they form have far from a uniform distribution. There are certain regions of the heavens much richer in nebulæ than others. In the northern hemisphere, the great region of nebulæ is near the pole of the galactic circle, or the part furthest removed in every direction from the Milky Way. In the southern hemisphere, the distribution is much more uniform.
We see, then, the aggregating power ascending by a series of steps till an elevation is attained, which makes the mind giddy to contemplate. The lowest term in this ascending series is the revolution of the satellite round the planet. The next is the revolution of the planet round the sun. Then comes the stellar grouping, by which each sun in its galaxy revolves round the centre of gravity of the whole, there being many intermediate steps formed by double stars and higher combinations. It had been attempted by Maedlar to prove that our firmament revolves round the bright star Alcyone in the Pleiades. The proof is, however, by no means satisfactory. A higher step still is presented by the revolution of one galaxy round another. No such revolution has been actually observed; but double nebulæ are found in such numbers, that the same reasoning; holds in their case as in that of the double stars. If the number of double stars warranted the inference of a physical connexion, a like inference is equally warrantable in the case of the nebulæ. It has been clearly ascertained, that our sun has a proper motion in space, carrying all its system of planets and satellites with it; and it has even been attempted to assign its probable velocity. According to the most reliable calculations, it advances on its path daily, by a space equal to its own semidiameter. This, combined with the detected motion of the double stars, warrants the presumption that revolution is not confined to the lower steps of grouping among the celestial bodies. There is a strong probability that every orb in the universe is in motion, and that all are related by one great bond of union. That gravitation is the great bond of connexion in the stellar spaces, as well as in the solar system, has been clearly ascertained. This is settled by the revolution of one star round another in an ellipse. The same power that determines the shape and the fall of a rain-drop, also determines the shape and the motions of the remotest galaxy.
The apparent magnitudes of the nebulæ are very various. The nebula in Andromeda, visible to the naked eye, has, when its minutest boundaries are brought into view, a length equal to five, and a breadth equal to two diameters of the moon. Again, there are nebulæ so minute, that a hundred might be packed within the circumference of the moon's disc.
The heavens are rich in colours; some clusters of stars glitter like a rich piece of jewellery, with gems of various colours. The nebulæ shine with similar colours. Sir John Herschel observed some in the southern hemisphere of a deep blue colour, without having any red associated with it. This seems to settle the disputed point, whether blue stars are blue in virtue of an inherent colour, or merely as complementary to the red stars, with which they are associated. It is now clearly established that there may be a whole galaxy of blue stars, tinging myriads of subordinate worlds with their sombre hue.
Though the study of stellar aggregation does not present such striking evidence of design as "we find in the system with which we are now immediately connected, still we cannot contemplate these strange forms, in connexion with the overwhelming magnitude of the scale in which they are presented to us, without feeling as if summoned into the presence-chamber of the Almighty. These firmaments, stretching indefinitely into the depths of space, afford a footing on which the inquiring spirit may tread, when yearning to realise the ideas of the Infinite and Eternal. It is wrong to despise such views of God as are perfectly familiar and palpable. Still, it is good to be brought face to face with parts of God's works whose design to us is unfathomable.
"It is the glory of God to conceal a thing, but the honour of kings is to search out a matter." The mind is irresistibly awed by the glory of God in the concealed mystery of these wondrous stellar groups; and though kingly intellects should unveil much of that mystery in the future march of science still, the lifting of the veil from one mystery, only reveals others far more glorious in their awful concealment. The philosopher who may be privileged to unveil the mysteries of these groups which now perplex us, will, after his task is done, feel, even more strongly than Newton, that he is only as a child gathering a few pebbles on the brink of the wide ocean.
In contemplating the various grades of stellar aggregations, the unity of plan is at once forced upon our minds, and, as a necessary inference, the unity of Him from whom the plan proceeded. From the fall of a stone, we trace the successive links, up to the revolutions of the remotest stars, and we find that one great law comprehends them all. The mighty plan is one, and the Architect must also be one. When we think of the Omnipotent guiding millions of shining suns in their spiral course, our hearts may sink within us as they speak to us of our insignificance in the vast plan. But another view quiets our spirits, at the same time chiding us for our unworthy thoughts of God: "Are not two sparrows sold for a farthing? and one of them shall not fall on the ground without your Father. But the very hairs of your head are all numbered. Fear ye not, therefore."