Fig. 76.—Sprayed Cluster below η in Hercules. see comparatively few. It would seem as if this oblate spheroidal arrangement was the result of a revolution of all the suns composing the system. Jupiter and earth are flattened at the poles for the same reason.
In various parts of the heavens there are small globular well-defined clusters, and clusters very irregular in form, marked with sprays of stars. There is a cluster of this latter class in Hercules, just under the S, in Fig. 72. "Probably no one ever saw it with
Fig. 77.—Globular Cluster. a good telescope without a shout of wonder." Here is a cluster of the former class represented in Fig. 77. "The noble globular cluster, ω Centauri is beyond all comparison the richest and largest object of the kind in the heavens. Its stars are literally innumerable; and as their total light, when received by the naked eye, affects it hardly more than a star of the fifth to fourth magnitude, the minuteness of each star may be imagined."
There are two possibilities of thought concerning these clusters. Either that they belong to our stellar system, and hence the stars must be small and young, or they are another universe of millions of suns, so far way that the inconceivable distances between the stars are shrunken to a hand's-breadth, and their unbearable splendor of innumerable suns can only make a gray haze at the distance at which we behold them. The latter is the older and grander thought; the former the newer and better substantiated.
Nebulæ.
The gorgeous clusters we have been considering appear to the eye or the small telescope as little cloudlets of hazy light. One after another were resolved into stars; and the natural conclusion was, that all would yield and reveal themselves to be clustered suns, when we had telescopes of sufficient power. But the spectroscope, seeing not merely form but substance also, shows that some of them are not stars in any sense, but masses of glowing gas. Two of these nebulæ are visible to the naked eye: one in Andromeda (see Fig. 68), and one around the middle star of the sword of Orion, shown in Fig.78. A three-inch telescope resolves θ Orionis into the famous trapezium, and a nine-inch instrument sees two stars more. The shape of the nebula is changeable, and is hardly suggestive of the moulding influence of gravitation. It is probably composed of glowing nitrogen and hydrogen gases. Nebulæ are of all conceivable shapes—circular, annular, oval, lenticular, conical, spiral, snake-like, looped, and nameless. Compare the sprays of the Crab nebulæ above ζ Tauri, seen in Fig. 79, and the ring nebula, Fig. 80. This last possibly consists of stars, and is situated, as shown in Fig. 81, midway between β and γ Lyræ.
Fig. 78.—The great Nebula about the multiple Star θ Orionis. (See Frontispiece.)