Orion Nebula

“ It is an education in the nebular theory of the universe merely to look at this spot with a good telescope. If we do not gaze at it long and wistfully, and return to it many times with unflagging interest, we may be certain that there is not the making of an astronomer in us.
Before quitting the Orion nebula do not fail to notice an eighth-magnitude star, a short distance northeast of the Great Nebula, and nearly opposite the broad opening in the latter that leads in toward the gap occupied by the Trapezium. ”

“ This he found “a work of great labour and difficulty.” While at the telescope he often half surrendered to despair “of ever being able to transfer to paper, with even tolerable correctness, its endless details.” “Language cannot easily convey,” he said, “a full impression of the beauty and sublimity of the spectacle this nebula offers when viewed in a sweep, ushered in by so glorious and innumerable a procession of stars, to which it forms a sort of climax.” Only the Orion nebula may be thought to surpass it in “magnitude, complexity, and brightness.” ”

“ They look to the unaided eye like misty specks, and require considerable attention to be seen at all. But in telescopes their appearance is marvellous. The Orion nebula is a broad, irregular cloud, with many brighter points, and a considerable number of stars intermingled with it, while the Andromeda nebula has a long spindle shape, with a brighter spot in the centre. It is covered and surrounded with multitudes of faint stars. It was only after astronomical photography had been perfected that the real shapes of the nebulæ were clearly revealed. ”

“ Its spectrum yields hydrogen, helium and nitrogen. The Orion nebula is receding from the earth about eleven miles in every second. Keeler and Campbell have shown that nearly every line of the nebular spectrum is a counterpart of a prominent dark line in the spectrum of the brighter stars of the constellation of Orion. A recent investigator of the distribution of luminosity in the great nebula of Orion finds that radiations from nebulium are confined chiefly to the Huygenian region of the nebula and its immediate neighborhood. ”

“ Its mass is almost infinitesimal and its attractive power on the earth practically nil. But a gaseous nebula having the same apparent size would have an enormous volume, and, although probably formed of very tenuous gas, its mass would be very great, and its attractive power considerable. The large apparent size of the Orion nebula shows that its volume is probably enormous, and as its attraction on the sun is not appreciable, its density must be excessively small, less than the density of the air remaining in the receiver of the best air-pump after the air has been exhausted. ”

“ Now, I do not say that it is inconceivable that an outlying star-system, so far off as to be irresolvable by any but the most powerful telescopes, should cover so large a space on the heavens. On the contrary, I do not believe that a galaxy resembling our own would be resolvable at all, unless it were so near as to appear much larger than the Orion nebula. I believe astronomers have been wholly mistaken in considering any of the nebulas to be such systems as our own. ”

“ In the heart of the Orion nebula are four small stars which constitute the well-known Trapezium. Situated as they are in the midst of this far-reaching mass of gas, it is not hard to picture them as centers of condensation, toward which the play of gravitational forces tends to concentrate the gases of the nebula. It might therefore be expected that stars in this early stage of growth should show through the spectroscopic analysis of their light some evidence of relationship with the surrounding nebula. Now this is precisely what the spectroscope has demonstrated. ”

“ On ordinary nights the nebula in Orion is a splendid object, and inspires the observer with amazement; but this is as nothing compared with the grand and magnificent sight which it presents during the very rare moments when our atmosphere is perfectly clear and steady. ”

“ It is as we approach the present time, and find the great nebula the centre of quite a little warfare among astronomers—now claimed as an ally by one party, now by their opponents—that we begin to attach an almost romantic interest to the investigation of this remarkable object.
In the year 1811, Sir W. Herschel announced that he had (as he supposed) detected changes in the Orion nebula. The announcement appeared in connection with a very remarkable theory respecting nebulæ generally—Herschel's celebrated hypothesis of the conversion of some nebulas into stars. ”

“ The most glorious object in the sidereal heavens, the Great Nebula in Orion, lies indeed in that southern hemisphere to which the younger Herschel's attention now became directed. It fortunately happens, however, for votaries of astronomy all the world over, that Nature has kindly placed her most astounding object, the great Nebula in Orion, in such a favoured position, near the equator, that from a considerable range of latitudes, both north and south, the wonders of the Nebula can be explored. ”

“ The Orion Nebula suggests the opened jaws of a fish or sea monster, hence called the Fish-Mouth Nebula. There is a Horse-Shoe Nebula, a Dumb-Bell Nebula, and many others of various shapes and forms. They are classified as follows: (1) Annular Nebulæ, (2) Elliptic Nebulæ, (3) Spiral Nebulæ, (4) Planetary Nebulæ, (5) Nebulous Stars, (6) Large Irregular Nebulæ.
Annular Nebulæ.—These resemble in appearance an oval-shaped luminous ring; they are comparatively few in number, and not more than a dozen [Pg 222] have been discovered in the whole heavens. ”

“ Our own sun’s corona flames out in every direction for more than 200 thousand miles, and should there be many suns eclipsed by the dark bodies in space might they not likewise, in some instances, present a nebulous appearance with a startling coronal effect? Theta Orionis, the wondrous multiple star, seemingly lying in Orion’s great nebula, is regarded as belonging to it because of its being in the same degree of the heavens; but although in the same degree it may be in quite a different plane, as light travels at the rate of over eleven millions of miles per minute. ”

“ The dark nebula is visible in the photographs as veil-like clouds obscuring the light of the stars beyond them, or, again, as definitely outlined black blotches lying like some huge object on a brilliantly glowing background. Such a 'blotch' is the Dark Bay or Dark Horse Nebula in Orion whose photograph is so fearfully suggestive and wonderfully beautiful.
Nebulous clouds are, in general, dark rather than luminous. These clouds are believed by many astronomers to be cosmic dust-particles driven out from bright stars. ”

“ But, what I do consider inconceivable is, that a nebula extending so widely, and placed (as supposed) beyond our system, should yet appear to cling (as the Orion nebula undoubtedly does) around the fixed stars seen in the same field with it. So strongly marked is this characteristic, that Sir John Herschel (who failed, apparently, to see its meaning) mentions among others no less than four stars—one of which is the bright middle star of the belt as "involved in strong nebulosity," while the intermediate nebulosity is only just traceable. ”

“ As their close allies, he now recognised planetary nebulæ, the “milkiness, or soft tint of their light,” agreeing much better with the supposition of a fluid, than of a stellar condition. And he rightly placed in the same category the Orion nebula, and certain “diffused nebulosities” which he had observed just to tarnish the sky over wide areas. These last might, he considered, be quite near the earth, and the object in Orion not more distant than perhaps an average second magnitude star.
The relations of the sidereal to the nebular “principle” exercised Herschel’s thoughts during many years. ”

“ Ten planetary nebulæ yielded perfectly satisfactory evidence of line-of-sight motion, [1531] the swiftest traveller being the well-known greenish globe in Draco, [1532] found to be hurrying towards the earth at the rate of forty miles a second. For the Orion nebula, a recession of about eleven miles was determined, [1533] the whole of which may, however, very well belong to the solar system itself, which, by its translation towards the constellation Lyra, is certainly leaving the great nebula pretty rapidly behind. The anomaly of seeming nebular fixity has nevertheless been removed ”

“ Moreover, a fairly bright adjacent nebula, perceived by O. Struve in 1868, and observed shortly afterwards by d'Arrest, has totally vanished, and was most likely only a temporary apparition. These are the most authentic instances of nebular variability. Many others have been more or less plausibly alleged; [1522] but Professor Holden's persuasion, acquired from an exhaustive study of the records since 1758, [1523] that the various parts of the Orion nebula fluctuate continually in [Pg 404] relative lustre, has not been ratified by photographic evidence. ”

“ But we find the unique multiple star apparently located in the richest part of the unique nebula. If, therefore, we remember that the region of the nebula referred to is perhaps about a square degree in extent, we are entitled to affirm that there must be forty thousand chances to one that Theta Orionis, the star, is veritably immersed in the glorious nebulosity of Orion. The theory of probabilities allows reasonable beings to draw no other conclusion. ”

“ The nebula around the strange variable star, Eta Argûs, is another remarkable instance of this sort. More than two years ago I ventured to make two predictions about this object. The first was a tolerably safe one. I expressed my belief that the nebula would be found to be gaseous. After Mr. Huggins’s discovery that the great Orion nebula is gaseous, it was not difficult to see that the Argo nebula must147 be so too. At any rate, this has been established by Captain Herschel’s spectroscopic researches. The other prediction was more venturesome. ”

“ Some detect with the naked eye the light that comes from the nebula in the Sword’s-Handle of Orion, which is thought to contain two trillions, two hundred billions of stars; and if all these stars are no nearer to each other than Alpha Centauri is to our sun, it cannot be otherwise than that some of them are so distant their light may have been travelling for a million years before it comes to our sight. ”

“ There is abundant evidence of this in the existing representations of the great nebula in Orion; a comparison of the drawings that have been lately made of this object, with the most perfect instruments and by the most skilful of astronomical draughtsmen, reveals varieties of detail and even of general appearance such as could hardly be imagined to occur in similar delineations of one and the same subject; and any one who himself makes a perfectly unbiassed drawing at the telescope will find upon comparison of it with others that it will offer many points of difference. ”

“ But, whatever may be associated in the nebula with the glowing gas which we see, the total amount of matter, invisible as well as visible, must be very small, or rather its average density must be very small, for the space occupied by such a nebula as that of Orion is so great that if the average density of its matter were equal to that of air the resulting mass by its attraction would exert a sensible effect upon the motion of the sun through space. ”

“ After a few years, however, when powerful telescopes showed that many of the nebulæ were only clusters of very minute stars, astronomers thought that Laplace's teaching had been wrong. But now the spectroscope has revealed to us glowing [Pg 153] gas actually filling large spaces in the sky, and every year accurate observations and experiments tell us more and more about these marvellous distant mists. Some day, though perhaps not while you or I are here to know it, Orion's nebula, with its glowing gas and minute star-dust, may give some clue to the early history of the heavenly bodies ”

“ In its brightest parts the nebula in Orion appears as a luminous cloud of a pentagonal form, from which issue many luminous appendages of various shapes and lengths. This principal mass is divided into secondary masses, separated by darkish, irregular intervals. These secondary masses in their turn appear mottled and fleecy. Towards the lower part of the pentagonal mass is found a roundish dark space, comparatively devoid of nebulosity, in which are involved four bright stars forming a trapezium, and several fainter ones. ”

“ The whole sextuple group makes a spectacle unique in the heavens. Wherever Theta Orionis happened to be in the sky it must necessarily be known as the most elaborately composed of all multiple stars. But, as a matter of fact, we find the wonderful star apparently occupying the most imposing site in the Great Nebula, so that the latter serves as a splendid setting to the complex star. ”

“ According to this view, our sun, with his attendant planets and comets, constitutes but a single star of the Galaxy, and our firmament of stars, or visible heavens, is composed of the stars of our nebula alone. An inhabitant of any of the other nebulæ would see spreading over him a firmament equally spacious, and in some cases inconceivably more brilliant.
It is an exalted spectacle to travel over the Galaxy in a clear night, with a powerful telescope, with the heart full of the idea that every star is a world. ”