The great variety of beauty that the planets present to us is sufficient to keep us always interested in them, when once we have acquired an acquaintance with them. Rarely is there an evening when some one of them does not enhance the charm of the splendid spectacle of the sky in which all the heavenly bodies save the sun have a part. Their greater brilliancy often brings them into view before the stars have begun to glow in the evening, and prolongs our sight of them after the rays of the sun have blotted out the light of the stars in the morning. Thus they are always single in their loveliness, and always hold a distinguished place in the midst of the brilliant company of the stars.

Having considered these brilliant bodies individually and in detail, as we have, we ought by this time to be able to identify any one of them that shows itself in the evening sky, and to have a pretty fair notion of the general character and peculiarities of each. But even if one does not much care for detailed information concerning them, or, before seeking that, prefers first to become familiar with their appearance, a quick and sure recognition of them may be had by noting their positions and their very striking individual aspects as set forth in the preceding chapters.

On seeing a bright object in the sky that does not seem to be a familiar star, simply stop and look at it. Does it twinkle? If it does not, it is a planet. If it is more than forty-five degrees from the sun, or if it is seen at a time when the sun has been down more than three hours, then it is neither Mercury nor Venus, and must be either Mars, Jupiter, or Saturn. Is it very bright and pinkish in tone? Then it is Jupiter. Is it very bright and quite red? It is Mars, not far from opposition. Is it not very bright, but small and rosy? Then it is Mars going toward conjunction. Is it yellow in tone and, while large and conspicuous, still not so very brilliant? It is Saturn.

If the planet we seek to name is nearer to the sun than forty-five degrees, but is still well above the horizon, it may be either of these three—Mars, Jupiter, Saturn—or it is Venus. If it is very bright and silvery, it is certainly Venus. If it is very low in the sky and very near the sun, it may be any one of the five visible planets. In such a position Mars will always be very small, and the others always larger than a first-magnitude star; and they may all twinkle a little—Mercury almost as much as a star. Their size will show them all (except Mars) as planets, but it will be somewhat more difficult to tell which is which than it is when they are higher up in the sky. The best thing to do in such circumstances is to look up their positions either in this book or in an almanac. The almanac will serve as a footman to announce them. The book, it is hoped, has so recorded their peculiarities and habits that either their appearance or their place will be sufficient to make them known.

In any event, the problem of identification in this position will not keep one long, for in a situation presenting these greater difficulties the planet will be visible for less than an hour after sundown. Besides, it is not likely at such times to attract one’s involuntary attention, but when under observation in such a situation is usually sought out by those already somewhat informed as to the planet’s habits and appearance, which will betray its identity. It is information of this sort that I have endeavored to give in these pages, and it is hoped that the reading of them will be the beginning of a long and intimate acquaintance with these charming and always interesting individuals.

Individuals the planets inevitably become to any one who learns to know them during the long, quiet nights in the country, or wherever an opportunity is afforded really to contemplate their peculiar traits and features. Like individuals of whatever kind, they impress different persons in different ways. As I have watched them from year to year I have come to have a very distinct impression of Jupiter as slow and majestic, and yet not lacking in joviality; Saturn as friendly, but reserved; Mars as sturdily brisk and busy; Venus as always gracious and smiling; and Mercury as irresponsible and roguish. Others might have an entirely different feeling in regard to them; but an intimate acquaintance with them, which is not wholly scientific, cannot fail to stamp them as in some sort individuals.

And when we consider that these interesting individuals are closely related members of our cosmic family, their ever-changing beauty of aspect, the history of their development and their affairs generally, gain a significance to us that no other heavenly bodies can have. The two groups of planets—the inner and the outer—are like two sets of children in a family: born of the same parent, but under very different circumstances, and in very different surroundings. Mars, the earth, Venus, and Mercury are all, as compared with the outer planets, small and dense, with more or less thin atmospheres and an abundance of heat and light. They all lie comparatively near to the sun, and are composed of the denser material lying near the center of the great nebula, which was the original form of the entire solar system. Probably denser to begin with than the others, they have, on account of their diminutive size, developed more rapidly and are further advanced toward the final state of solidity which we shall all attain in the end. Mercury, the smallest, is already old and seamed and hardened. Mars, the next in size, is well advanced, but still has an atmosphere and some other signs of vitality. Venus, though we know so little about her, has probably a long period of development yet before her; while this warm, nourishing earth, which seems to us the best one of them all, will probably for a still longer time than Venus hold its atmosphere and remain green and flourishing.

On the other side of the vast space which divides the two groups of the sun’s family dwell Jupiter, Saturn, Uranus, and Neptune. They are all tremendous in volume, enveloped in immense atmospheres, far, far from our common source of heat and light, of comparatively slight density, and probably formed from the lighter material composing the outer edges of the parent nebula, and, because of their immense size, still in a very early stage of development. The two groups could scarcely seem more widely different if they belonged to different systems; but the members of each are all closely akin, and each one in its own way, determined by its size and environment, is developing toward the same end.

If there is life on any of these outer planets, it must be of a sort of which we have no conception. Jupiter and Saturn are probably red-hot, and could sustain nothing more cold-blooded than a race of salamanders, though why a race of intelligent salamanders should or should not exist there, is a question that one might make bold to answer according to one’s fancy. Uranus and Neptune are smaller, and perhaps less hot than Jupiter and Saturn; but we really know very little about the state of their domestic affairs, and the little we do know in no way indicates a place of abode for any sort of intelligence conceivable to us. We can, however, conceive of a time in the far-distant ages when these four hot and vaporous planets may have become sufficiently condensed to have a solid crust, and yet have sufficient internal heat to moderate the frigid temperature that would be normal at their distance from the sun, and they might then support life even somewhat resembling and perhaps even more gloriously beautiful than that with which we are familiar.

Of the existence of life somewhat similar to ours on the smaller, near-by planets we may have something nearer a reasonable conception, though we are nowhere near the possession of any real knowledge concerning it. Mercury, we have every reason to think, cannot support life, mainly because of his lack of atmosphere; but also because of his long rotation, which affords no alternations of day and night, but leaves him with one side always burning-hot and the other inconceivably cold. Venus might very well have a climate not utterly unlike ours, and hence be habitable for beings somewhat resembling us, if she has, as she has long been thought to have, a heavier atmosphere than the earth has, and if she has alternations of day and night. But we have seen that, owing to the obscurity of the surface of Venus, our knowledge in regard to these conditions is far from certain, and we have little reason to have even speculative ideas concerning life there. With Mars it is a more open question. We can see that planet, and see it fairly well. It has an atmosphere and changes of seasons, and while it may not afford a climate that would be exactly attractive to us as a place of transmigration, it is not particularly unreasonable to let our fancy play over the rather pleasant speculation concerning the presence there of beings at least understandable by us, even if not wholly congenial.

Whatever each planet affords in the way of life and human interests, all of them must ever be to us the most interesting things in all nature, outside of our own earth, in the two regards already pointed out: first, as the most beautiful objects of vision among all the starry hosts, and, second, as our nearest kindred in this universe of suns and systems of worlds. Together the earth and they circle ceaselessly around and around the sun, following in nicely adjusted orbits that great luminary as it sweeps majestically on through space toward the beautiful Vega, itself a sun, and, so far as we now know, in this close companionship we shall continue until every planet and the sun itself has become cold and dark and lifeless. And then, perhaps, or even before the light of our system is finally extinguished, we may meet another wandering sun, and in the marriage of the two great bodies another system of worlds may be evolved of which we and the planets shall form a part.