Space and Other Suns
N OW you understand how the sun and his family might look if you saw them from a very great distance, don't you? The sun is in the center and all the planets are moving around him each in a separate orbit. Each planet moves round and round its orbit forever. It belongs to the sun. All the planets together make the solar system. The whole system together is in the midst of space.
Thousands of other systems like our own are in space also. Space is just endless. There is room in it for everything. We can not imagine any end to it at all. All the stars that we see in a bright night are in this endless space. Every one of the stars is a sun very much like our own sun. There is good reason to suppose that very many of these stars (suns) have planets of their own moving around them, just as the earth and the other planets move around our sun. Why should it not be so?
If you look out at the stars on any clear night you will see about two thousand of them. (I suppose you thought you would see many more, but they have all been counted and named—or at least numbered—so that we know just how many there are.) On any one clear night, at any one place, you can see about two thousand.
If you travel to different places on the earth, and count all the different stars you can see at all times of the year, and if you make a map of them so as to be sure to count no one of them more than once, you will find that you can see about six thousand in all with your bright eyes.
Each one of the stars may have planets of its own. We do not positively know that there are any such planets to other suns than ours, but there may be. Why not? If our sun has eight planets, these six thousand stars (suns) may have
Forty-eight thousand planets! That seems a large number, doesn't it? But it is not even a beginning.
With a large telescope you can see not only the six thousand bright stars visible to your eye, but millions of others that are too faint for you to see with the naked eye, but bright enough to show in the telescope. That is what telescopes are for—to show things that are too faint to be seen with the eye alone.
Even a common opera glass will show you thousands of stars that you have never seen before. Try it! Look with your eye at a place in the sky at night, and count the stars that you can see in some small region; then look at the same place with your opera glass and you will see many, many more stars.
A large telescope will show you many thousand times more than you can see with the opera glass. The great telescope of the National Observatory at Washington would show, perhaps, a hundred million stars.
I confess that they have not all been mapped or counted, but a great many of them have been photographed, and a few of the photographs have had their stars counted. So I think that a hundred millions are not too many.
Now every one of these millions of stars is a sun, very
much like our own sun, and there is no reason to say
that each one of them may not have at least eight
Eight hundred million planets!
We do not absolutely know that any of these planets exist, but there is no good reason why they may not exist. At any rate, we have a right to think about it. There are some very good reasons for believing that very many of the stars (suns) have a family of planets, just as our star (the sun) has its family. Probably some of the stars have a family of more than eight planets, perhaps sixteen or twenty-four. Why not? And no doubt there are many stars that have a small family of perhaps four or even two planets. And there are probably other stars that have no planets at all moving around them—childless stars they would be.
But, so far as we can know, there are reasons for thinking that these millions of stars (suns) shown in a large telescope have millions of planets belonging to them.
Each star is, as it were, the chief of a family. Its planets belong to it; they do not leave it to go away to other stars. They move around it in circles, or rather in ellipses, just as the earth moves around the sun, and they turn around on axes, just as the earth turns around on its axis. One turn around the axis makes a day and a night. The side of the planet turned toward its sun gets shined upon, and has daytime. The other side that is turned away from its sun is in the dark, and has night-time. Every planet has its day and night, then, just as we have it on the earth.
The earth in its path goes around our sun and makes a complete journey in one year, and has its seasons of spring, summer, autumn, and winter in a year. In the same way each one of the millions of planets goes around its own star (sun), the chief of its family, in an orbit of its own, and has its own seasons like spring and summer, and so forth. Why not? Is there any reason you can think of, why not?
Now you are going to ask me if these millions of planets are inhabited—if they have men on them. No one really knows. But we can think about it. It will be easier to decide what to think a little later on, after we have studied the planets of our own family a little more. When we know something more about Mercury, and Venus, and Mars, and Jupiter, and the rest, we can judge better about the planets that belong to other families.
You have to imagine the whole of space extending in all directions everywhere. It is quite endless. You can think of it as a huge globe if you like. Within this immense globe of Space there are millions upon millions of stars, each star a sun, and each star with some planets in its family. Some stars have more planets, some fewer.
These stars seem to be close together when we look at them in the sky. But they are usually not close together at all. They are usually very far apart indeed. It is an immense distance from our sun to the star that is nearest to us. Look up in the sky and see how very far away the stars seem to be. They really are immensely far off. Each one of the stars that you see is at least as far away from every one of its neighbors as our sun is from the nearest stars.
Space is filled with stars, no doubt. But they are not near together like the houses in a city. You must think that each one of them is as far away from its neighbors as our sun is from the nearest of these stars. Try to think about it, and see if you can imagine it all with your eyes shut. Space—millions of stars in it—each star a sun—no star nearer to another star than our sun is to the nearest star. Think about it, and you will get some faint idea of how large space really is.
The earth is really the most insignificant thing—the smallest thing—when you think about it in this way. It is very important to us, no doubt, but what do you suppose a person in the Great Bear (if there are any persons there) would think about us?
What do you think about them? That is the answer to the question. Probably you have not thought about such a world as theirs as even possible, have you? Well, you know now that it is possible at any rate. Space is full of planets and stars, and instead of thinking about them as if they were mere glittering points scattered over the surface of the sky you must imagine them as far more interesting.
When you see a sky full of stars you must think of each one of them as a huge sun, with a family of planets around it. It isn't a mere spark of light. It is the center of some family, and perhaps it is quite as important as our own solar family. Why not?
If you can think of the universe—of all the stars, and suns, and planets—in this way, it will be a thousand times more interesting than it ever was before, will it not? The more you know about it the more interesting it will be. And the way to learn is to study the different planets of our own family and to see how matters stand with them. If we know something about our nearest neighbors this something will help us to understand our very distant neighbors.
Even the planets, which are our nearest neighbors, are very far away from us, and we know very little indeed about them compared to what we should like to know. Instead of being like the earth they are generally wonderfully different from it. The sun is something like a blazing fire. The moon is colder than the coldest ice. It is so cold that even quicksilver would freeze solid in an instant if a thermometer were taken there, and you know we put quicksilver in our thermometers, because it remains liquid except near the north pole. The moon is far colder than any part of the earth—much colder than even the arctic regions.
The planet Mercury is very far away from the sun if you measure its distance in miles, but it is very much nearer to the sun than we are, and it must receive very, very, much more heat from the sun than we do, just for that reason. The nearer a person goes to the sun the hotter he will be. Our summers on the earth are hot enough, aren't they? Well, just think how hot it would be if the earth were placed as close to the sun as Mercury is!
You see that even in our own family of planets there are many kinds of conditions. In the different families of planets that belong to the different suns (stars) the conditions are even more various. To understand them we must study our own planets. And if we can find out even a little about them it will help us to discover something about the circumstances on other worlds than ours.
Do not forget, all this while, that the stars and our sun are like each other, because they shine by their own light, as a candle or an electric light shines by its own light. And all the planets of our family—Mercury, Venus, Jupiter, Saturn, and so forth—are like each other in one thing at least. No one of them shines by its own light. They only shine by light reflected from the sun.
If you hold up a ball near a candle or an electric light at night, the ball will be bright on the side that is turned toward the light (and, of course, darker on the other side). It is just so with the planets. No one of them has any light of its own. If there were no sun you would never see the planets at all.
They might be there all the time, but you would not know they were there, because they would reflect no light to you. Our moon, too, shines by the sun's light. If the sun were suddenly snuffed out, as a candle sometimes is, the moon would send out no light. None of the sun's light would shine on the moon then, and so no light would come from the moon to us.
In one special way, then, the planets are very different from the sun. The sun and all the stars shine by their own light. The planets and the moon shine by sunlight, not by their own light. This is one of the many differences between planets and suns, and it is, perhaps, the most striking one of all. You must not forget it.