For the astrology and poetry and romance of the planets one must go elsewhere. Nearly every book on the subject of the planets—and there are many of them—has some information about these things; and properly, too, for every genuine emotion and every real fancy has its value. But neither curious lore of the planets nor the sentiment and emotion they have produced in others is what the author of this book is striving to set forth. It is something much more vital than this. What we wish to contemplate here are the plain facts, the knowledge of which enlivens and enriches one’s mind and nature. If the contemplation of them kindles one’s fancy or excites one’s emotions, these results at least will not be second-hand. If the bare facts, simply and plainly told, and the view of the planets themselves as they wander through their courses in the sky, do not awaken one’s understanding and imagination, no amount of poetry or romance that other people have built up around the planets will arouse anything more than a factitious interest in them. It is when our own faculties are at work and our own fancy plays over a subject that we become genuinely and lastingly interested in it.
The facts themselves are in the main quite simple, and will not be given here as anything else than that. They have been fairly wrested from that mysterious thing called space by the mighty power of mind and unceasing labor. Our knowledge of them is due to long nights of watching and long days of calculating; to long and careful testing and considering of theories, only to find that something else must be tried; to courage to begin all over again, to sudden inspirations, and sometimes to those lucky discoveries that seem almost like miracles.
The subject of the planets has in some respects a greater interest even than that of the stars, because we know, after all, more about them. We sometimes have a feeling, though, that we know more of the stars, although the stars are so much farther off. Why we have this feeling it is easy to explain. Knowing them to be so far removed from us, we really approach the stars with a different expectation. The few things that we have learned about them have in themselves such a magnitude that it makes them seem a greater body of knowledge than they truly are. The stars are indeed so far away, and what we know of them has to be expressed in such large terms, that the mind does not demand in that information the minute exactness that it seeks for in the case of nearer objects.
In the case of the stars, we seek mainly to know their distances, the direction of their motions, the speed with which they travel, and their probable connection with each other. The fact that in computing the distance of a single star, many trillions of miles away, the result may be a little less than exact does not keep us from learning what ones are sufficiently near for their distances to be measured at all and what ones are immeasurably remote. Whether they travel at the rate of exactly three or three hundred miles a second, we can learn that some are traveling at somewhat the same rate of speed as our sun travels, and some incredibly faster; that certain groups are going in one direction and certain groups in another; that some are approaching us and some are receding from us. And thus we can classify them and learn the significance of these facts, and, little by little, gain a definite understanding of the construction and meaning of the entire universe. Their very remoteness gives a certain compactness to the information we have about the stars, by making it necessary to generalize more than we would if they were near enough to yield more details; and we are in a way satisfied with this more general sort of knowledge of them.
But the very fact of our knowing so much about the planets extends our curiosity concerning them and makes us feel that we ought to know more. The mind is provoked into more minute speculations about them, and we demand more exactness of information and knowledge of a more specific or intimate sort than would satisfy us in regard to the stars. Atmosphere, habitability, exact size, seasons, and day and night, are the kind of things we most seek to know in reference to the planets. These are such definite things that conclusions concerning them are subject to close criticism, and differences of opinion in regard to them thus sometimes occur which tend to give one a more or less confused notion of what is really known. As a matter of fact, our information about the planets is much fuller than our knowledge of the stars, as we would naturally expect it to be. Much of what we seek to know about the stars has long been common knowledge about the planets.
II
OUR RELATION TO THE PLANETS
To know about the planets is to know about ourselves. The earth is one of them. Whatever their origin, the earth’s is the same. It and they are formed from the same nebula, controlled by the same central body, subject to the same laws, and destined for the same fate in the end. In this, the stars and the planets are not alike. They all shine upon us with the same sweet friendliness, and commonly we make no difference between them in our feeling for them. But the stars are bright and beautiful acquaintances living far away in their own domain. The planets are members of our own family, bone of our bone and flesh of our flesh, living comparatively near to us, within the domain of our common source of life, the sun.