By the same physical laws that caused our Earth once to be hot, the Sun shines to-day. Only its greater size has given it a life and a brilliancy denied to smaller orbs. The falling together of the scattered particles of which it is composed, caused, and still is causing, the dazzling splendor it emits. And so long as it remains gaseous, its temperature must increase, in spite of its lavish expenditure of heat, as Homer Lane discovered forty years ago.
But the Sun’s store of heat, immense as it is to-day, and continued as it is bound to be for untold æons by means of contraction of its globe upon itself, and possibly by other causes, must some day give out. From its present gaseous condition it must gradually but eventually contract to a solid one, and this in turn radiate all its heat into space. Slowly its lustre must dim as it becomes incapable of replenishing its supply of motive power by further shrinkage in size. Fitfully, probably, like Mira Ceti to-day, it will show temporary bursts of splendor as if striving to regain the brightness it had lost, only to sink after each effort into more and more impotent senility. At last some day must come, if we may talk of days at all when the great event occurs when all days shall be blotted out, that the last flicker shall grow extinct in the orb that for so long has made the hearth of the whole system. For, presciently enough, the Latin word focus means hearth, and the body which includes within it the focus about which all the planets revolve also constitutes the hearth from which they all are lighted and warmed.
When this ultimate moment arrives and the last spark of solar energy goes out, the Sun will have reverted once more to what it was when the cataclysm of the foretime stranger awoke it into activity. It will again be the dark body it was when our peering into the past first descries it down the far vista of unrecorded time. Ghostlike it will travel through space, unknown, unheralded, till another collision shall cause it to take a place again among the bright company of heaven. Thus, in our account of the career of a solar system, we began by seeing with the mind’s eye a dark body travelling incognito in space, and a dark body we find ourselves again contemplating at the end.
In this kaleidoscopic biograph of the solar system’s life, each picture dissolves into its successor by the falling together of its parts to fresh adjustments of stability, as in that instrument of pleasure which so witched our childish wonder in early youth. Just as when a combination had proved so pretty, once gone, to our sorrow no turning of the handle could ever bring it back, so in the march of worlds no retrace is possible of steps that once are past. Inexorable permutations lead from one state to the next, till the last of all be reached.
Yet, unlike our childhood’s toy, reasoning can conjure up beside the present picture far vistas of what preceded it and of what is yet to come. Hidden from thought only by the distraction of the day, as the universe to sight lies hid by the day’s overpowering glare, both come out on its withdrawal till we wonder we never gazed before. Our own surroundings shut out the glories that lie beyond. Our veil of atmosphere cloaks them from our view. But wait, as an astronomer, till the Sun sinks behind the hills and his gorgeous gold of parting fades to amber amid the tender tapestry of trees. The very air takes on a meaning which the flood of day had swamped. Seen itself, no longer imperfectly seen through, it wakes to semi-sentient existence, a spirit come to life aloft to shield us from the too immediate vacancy of space. The perfumes of the soil, the trees, the flowers, steal out to it, as the twilight glow itself exhales to heaven. In the hushed quiet of the gloaming Earth holds her breath, prescient of a revelation to come.
Then as the half-light deepens, the universe appears. One by one the company of heaven stand forth to human sight. Venus first in all her glory brightens amid the dying splendor of the west, growing in lustre as her setting fades. From mid-heaven the Moon lets fall a sheen of silvery light, the ghostly mantle of her ghostlike self, over the silent Earth. Eastward Jupiter, like some great lantern of the system’s central sweep, swings upward from the twilight bow to take possession of the night. Beyond lies Saturn, or Uranus perchance dim with distance, measuring still greater span. All in order in their several place the noble cortège of the Sun is exposed to view, seen now by the courtesy of his withdrawal, backgrounded against the immensity of space. Great worlds, these separate attendants, and yet as nothings in the void where stare the silent stars, huge suns themselves with retinues unseen, so vast the distances ’twixt us and them.
No less a revelation awaits the opening of the shutters of the mind. If night discloses glimpses of the great beyond, knowledge invests it with a meaning unfolding and extending as acquaintance grows. Sight is human; insight seems divine. To know those points of light for other worlds themselves, worlds the telescope approaches as the years advance, while study reconstructs their past and visions forth their future, is to be made free of the heritage of heaven. Time opens to us as space expands. We stand upon the Earth, but in the sky, a vital portion not only of our globe, but of all of which it, too, forms part. To feel it is to enter upon another life; and if to realization of its beauty, its grandeur, and its sublimity of thought these chapters of its history have proved in any wise the portal, they have not been penned in vain.