Star-Clusters and Nebulæ.
Fig. 624.—Nebulæ in Pegasus.
Nebulæ and Star-clusters are numerous in the heavens. The most important are the Great Nebulæ in Orion and in Andromeda. But there are other very beautiful “patches” of luminous matter or cloud appearances composed of minute stars invisible to the naked eye. We annex specimens of the Nebulæ, one or two having been already inserted. There must be thousands of these star-clouds, and they have been classified by Sir John Herschel from Sir William’s discoveries as follows:—
(1) Clusters of stars, in which the stars are clearly distinguishable, divided again into regular and irregular clusters.
(2) Resolvable Nebulæ, which may be separated into distinct stars under powerful telescopes.
(3) Nebulæ, in which there is no appearance whatever of stars, divided into classes according to brightness, etc.
(4) Planetary Nebulæ.
(5) Stellar Nebulæ.
(6) Nebulous Stars.
