Dr. Max Wolf. THE GREAT NEBULA IN ANDROMEDA.Dr. Max Wolf.THE GREAT NEBULA IN ANDROMEDA.
If you take an imaginary line down from the two left-hand stars of Cassiopeia, and follow it carefully, you will come before long to a rather faint star, and close to it is the nebula.
When you catch sight of it you will, perhaps, at first be disappointed, for all you will see is a soft blur of white, as if someone had laid a dab of luminous paint on the sky with a finger; but as you gaze at it night after night and realize its unchangeableness, realize also that it is a mass of glowing gas, an island in space, infinitely distant, unsupported and inexplicable, something of the wonder of it will creep over you.
Thousands of telescopic nebulæ are now known, and have been examined, and they are of all shapes. Roughly, they have been divided up into several classes—those that seem to us to be round and those that are long ovals, like this one in Andromeda; but these may, of course, be only round ones seen edgewise by us; others are very irregular, and spread over an enormous part of the sky. The most remarkable of these is that in Orion, and if you look very hard at the middle star in the sword-hilt of Orion, you may be able to make out a faint mistiness. This, when seen through a telescope, becomes a wonderful and far-spreadingnebula, with brighter and darker parts like gulfs in it, and dark channels. It has been sometimes called the Fish-mouth Nebula, from a fanciful idea as to its shape. Indeed, so extraordinarily varied are these curious structures, that they have been compared with numbers of different objects. We have some like brushes, others resembling fans, rings, spindles, keyholes; others like animals—a fish, a crab, an owl, and so on; but these suggestions are imaginative, and have nothing to do with the real problem. InThe System of the StarsMiss Clerke says: 'In regarding these singular structures we seem to see surges and spray-flakes of a nebulous ocean, bewitched into sudden immobility; or a rack of tempest-driven clouds hanging in the sky, momentarily awaiting the transforming violence of a fresh onset. Sometimes continents of pale light are separated by narrow straits of comparative darkness; elsewhere obscure spaces are hemmed in by luminous inlets and channels.'
One curious point about the Orion Nebula is that the star which seems to be in the midst of it resolves itself under the telescope into not one but six, of various sizes.
Nebulæ are in most cases too enormously remote from the earth for us to have any possible means ofcomputing the distance; but we may take it that light must journey at least a thousand years to reach us from them, and in many cases much more. Therefore, if at the time of the Norman Conquest a nebula had begun to grow dim and fade away, it would, for all intents and purposes, still be there for us, and for those that come after us for several generations, though all that existed of it in reality would be its pale image fleeting onward through space in all directions in ever-widening circles.
That nebulæ do sometimes change we have evidence: there are cases in which some have grown indisputably brighter during the years they have been under observation, and some nebulæ that have been recorded by careful observers seem to have vanished. When we consider that these strange bodies fill many, many times the area of our whole solar system to the outermost bounds of Neptune's orbit, it is difficult to imagine what force it is that acts on them to revive or quench their light. That that light is not the direct result of heat has long been known; it is probably some form of electric excitement causing luminosity, very much as it is caused in the comets. Indeed, many people have been tempted to think of the nebulæas the comets of the universe, and in some points there are, no doubt, strong resemblances between the two. Both shine in the same way, both are so faint and thin that stars can be seen through them; but the spectroscope shows us that to carry the idea too far would be wrong, as there are many differences in constitution.
We have seen that there are dark stars as well as light stars; if so, may there not be dark nebulæ as well as light ones? It may very well be so. We have seen that there are reasons for supposing our own system to have been at first a cool dark nebula rotating slowly. The heavens may be full of such bodies, but we could not discern them. Their thinness would prevent their hiding any stars that happened to be behind them. No evidence of their existence could possibly be brought to us by any channel that we know.
It is true that, besides the dark rifts in the bright nebulæ, which may themselves be caused by a darker and non-luminous gas, there are also strange rifts in the Milky Way, which at one time were conjectured to be due to a dark body intervening between us and the starry background. This idea is now quite discarded; whatever may cause them, it is not that. One of the most startlingof these rifts is that called the Coal-Sack, in the Southern Hemisphere, and it occurs in a part of the sky otherwise so bright that it is the more noticeable. No possible explanation has yet been suggested to account for it.
Thus it may be seen that, though much has been discovered, much remains to be discovered. By the patient work of generations of astronomers we have gained a clear idea of our own position in the universe. Here are we on a small globe, swinging round a far mightier and a self-luminous globe, in company with seven other planets, many of which, including ourselves, are attended by satellites or moons. Between the orbits of these planets is a ring or zone of tiny bodies, also going round the sun. Into this system flash every now and then strange luminous bodies—some coming but once, never to return; others returning again and again.
Far out in space lies this island of a system, and beyond the gulfs of space are other suns, with other systems: some may be akin to ours and some quite different. Strewn about at infinite distances are star clusters, nebulæ, and other mysterious objects.
The whole implies design, creation, and theworking of a mighty intelligence; and yet there are small, weak creatures here on this little globe who refuse to believe in a God, or who, while acknowledging Him, would believe themselves to know better than He.
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