Nebula

(něb'ū-lah,) pl. NEBULE. [L., ava por.] (Ast.) The name given to certain luminous spots in the heavens, many of which the telescope resolves into groups of stars, whilst others resist the power of the best instruments, although astronomers are led to think that irresolvable neb ulæ are also groups of stars. Some nebulse have very fantastic or complicated shapes, and most of them undergo great change in appearance, according to the power of the telescope with which they are viewed. Nebulæ have been thus cla ed: 1. Those that are resolvable into clusters of stars; some are globular, others elliptic (Fig. 490), others of an irregular figure. 2. Such as lead the observer to suspect that Fig. 490.- NEBULE, NEAR THE BELT OF ANDROMEDA. they consist of stars, and would be resolved by telescopes of higher power. 3. True neb ulæ, in which there isnot the slightest appearance of stars, with the highest powers that can be directed to them. 4. Planetary neb ulæ, which have exactly the appearance of planets, and are of immense magnitude; their light must be most brilliant. 5. Stellar neb ulæ, whose nebulous matter is greatly and suddenly condensed towards the centre; and 6. Nebulous stars, which are brilliant stars, surrounded by a perfectly circular disk or atmosphere of faint light. Upwards of 5,000 neb ulæ have been catalogued.. [s. 635] IMG:p0680_0.jpg:Gravür