The pictures we have been looking at disclose clouds of suns in our Milky Way galaxy. Their number is beyond our powers to comprehend. However, it must be understood that all space is not thus crowded with suns. From our particular location inside the galaxy our view of things is quite different from what it would be were we outside looking in. Located where we are, close to the equatorial plane and not far from the axis of the entire affair, we look through the long way when we gaze along the equatorial plane. We therefore see a lot of stars. But when we look at right angles to this plane, we look through only half the thickness of the "dish'" Since the "dish” is thin as compared with its diameter, we see fewer stars.
The equatorial view is that in which we indulge when we look overhead on a clear night and see the irregular haze extending from horizon to horizon. When we point our telescope in that direction and take a picture, we resolve the haze into individual suns. But when we point our telescope at a lower angle and take a picture, we get many stars, but nothing to compare with what we get in the overhead view.
Our Sun is one of the vast horde of suns we see in the photographs. Our Sun has satellites. Is our Sun the only one in all that vast horde to have satellites? We must acquire some sort of concept of the number of suns from which we can derive an idea of the density of celestial "population." From this we can infer tire chances of near-collisions occurring, such as occurred in the case of our Sun and brought us into being.
Astronomers and mathematicians have become so bold that they not only dare estimate the number of suns in the Milky Way galaxy, but actually have the temerity to calculate the total weight of the galaxy, its age, and several other of its characteristics. They would have been burned at the stake with enthusiasm three centuries ago for daring to venture into such matters.
Seares estimates there must be something of the order of 10,000 million suns in the Milky Way. Shapley estimates 100,000 million. Eddington estimates that the galaxy weighs 270,000 million of our suns. If we take Shapley’s number estimate of 100,000 million suns and Eddington's weight estimate of 270,000 million suns, it might be thought that our Sun is very much below the average, even though we make a generous allowance for the weight of the non1uminous that we believe exists there. We do not know much about these matters, but from such evidence as we have we are led toward the conclusion that our Sun is probably below rather than above average, which is quite a different story from what our forebears attempted to have us believe.
The gravitational pull of the entire aggregation holds the outermost suns from getting away. Our Sun is journeying around among the others, taking a path which is decided by the gravitational pull of its fellows and the momentum that was imparted to it when it was born. Every other one of the thousands of millions is doing the same thing. About 2,000 million years ago our Sun seemed to have encountered one of its neighbors, and we are one of the indirect results. 'Was ours the only sun ever to have such an experience, is the big question con- fronting us.
The element of time needs to be considered here. Jeans, in his compelling way, speaks of the effect of time and plenty of it. Quoting from Huxley, he says that from the law of chance it can be computed that were six monkeys to be set strumming six typewriters for enough millions of years, they would, purely by chance, write every book in the British Museum.
If this is right, then it would seem to follow that if millions enough of suns roamed around in a galaxy for millions enough of years, every sun would have every experience that could be had. How many millions of years are there available? Jeans estimates some 5 to 10 million million years as the age of our particular Sun. During that interval at least one sun, ours, encountered an experience which indirectly produced life. Jeans estimates, in discussing this point, that the chances of a sun having had such an experience as our Sun are about 1 in 100,000. If this means that one sun in every 100,000 is likely to have had an experience that would produce planets, then a great many suns in our Milky Way galaxy must have planets.
The chances of life are still further reduced, it must be conceded, by the fact that even were a sun to have planets, one of these must be just far enough away, and not too far away, to maintain for 300 million years a temperature that shall not go much above 150 degrees Fahrenheit or much below 100 degrees below zero Fahrenheit in order to beget an intelligence such as yours and mine. But, even so, there are somewhere between 10,000 million and 100,000 million suns dodging around in our galaxy, and they are thought to have been doing it for something like 5 to 10 million million years. Have we not grounds that justify us in speculating as to the possibilities in this direction ? It has seemed to the writer that we have. But let us proceed in our attempt to gain a little more knowledge before we draw too many conclusions regarding the existence of life elsewhere than on our Earth.
Up to the time when we came to understand that tire Milky Way was an enormous aggregation or swarm of individual stars, we used the word "universe" to indicate all celestial matter. However, in examining the Milky Way we uncovered another and still more astonishing fact. This was that as our larger and larger telescopes and cameras penetrated deeper and deeper into space, other galaxies of stars were disclosed. Each year saw the number of these galaxies added to until the disconcerting fact stared us in the face that the deeper we penetrated into space, the more Milky Ways we uncovered. Obviously our definition of the word "universe" had to be modified. It thus came about that we selected the word "galaxy" to indicate the aggregations and for an all-embracing term the word "cosmos" instead of "universe." We refer to the aggregation of which our Sun is an insignificant member as the "Milky Way galaxy" and to all other galaxies as being "extra-galactic" or "island universes." All the stars we see ordinarily in the sky with our unaided eyes are members of our Milky Way galaxy. Only by careful viewing, aided by an ex- pert, are we likely to see a light that is extra-galactic.
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