Up to this point we have dealt principally with stars, which are suns, having surface temperatures which range between 1,500 degrees and 30,000 degrees Fahrenheit. All thought f life on them is, of course, entirely out of the question. In fact, excepting Moon, and Mars, and the more remote planets, most of the matter of which we have become conscious thus far is thousands of degrees hot.
The telescope and the camera disclose other bright objects in our galaxy besides stars. When astronomers gradually mapped cut the details of the Milky Way they became conscious of areas of haze. Recalling Galileo’s experience, more powerful and still more powerful magnifications were brought to bear on them. But at the greatest attainable magnification these haze spots remained haze and could not be resolved into individual stars. They appeared to be gaseous in the spectroscope, and they were, of course, hot or they would not radiate. These bright hazes we call “nebulae.” An interesting and a suggestive example of a nebula is shown in Figure 22. Here we have an extremely impressive picture of filmy clouds of some kind of matter. We should be totally ignorant of its existence were it not for the reflected light from a near-by star. A study of this picture discloses light reflected from what appear to be wisps of matter at enormous distances from the central mass. The spotty effect all over the picture is caused by the various suns between us and the nebulosity.
After years of study and observation, it developed that there were different kinds of nebulae. There appeared to b a type that had a bright spot as a nucleus which was surrounded by an annular ring of haze. They are in our Milky Way galaxy, and several hundred of them have been seen. We call them “planetary nebulae.” We cannot account for them satisfactorily, and as they appear to offer no hope regarding life, we pass them by. Another kind of matter occurring in our galaxy appears to be enormous clouds of chaotice gas. The only explanation we can give of these is that they are made up of gases existing in states all the way from an unimaginable degree of attenuation to colossal concentrated masses as enormously high temperatures. Whether they represent a cataclysm such as our Sun experienced we have no idea, but we cannot but have this in mind when we see them. The great nebula in Orion’s Sword shown in Figure 23 is a good example of stray, disorganized, and highly confused gas. It has no geometric structure. It represents titanic turmoil and chaos. If our forebears had known about it, unquestionably they would have told us it was Hell. It fits their description admirably. The spectrum shows hydrogen, helium, and another gas which we have not yet found on Earth, nebulium. The distance of this nebula is something of the order of 6oo light years. Its breadth, as we see it, is about six light years. Many stars that shine brightly in the midst of the nebula are either near it or a part of it. What can possibly be going on there we cannot imagine, but something very dreadful indeed must have happened to upset the celestial order as this picture discloses.
Figure 23 revives interest in those mysterious dark areas. There are evident several dark places that suggest something very tangible in the way of cool matter. If they are fairly near the great mass of hot gas and if they are cooled solid bodies in great swarms, they at once be- come interesting to speculate about as a possible abode of life. We do not know enough yet to form any kind of intelligent opinion. There is nothing left us but to await the efforts of the physicists to develop means of photo- graphing them or otherwise gaining some idea as to their constitution; of the mathematicians for computing their weights, dimensions, temperatures, and ages; and of the astronomers for disclosing their motions and their near-by neighbors.
There is still another kind of nebulae, to be discussed in the next chapter. Being extra-galactic, they are not part of our Milky Way, but are other Milky Ways. They seem to exist in various stages of development from birth to old age, and they suggest many things that we can apply to our galaxy. They are away off in the remote reaches of space, and the finest instruments are necessary to photograph them. We shall see pictures of them which would have frightened the forefathers.
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