The Horsehead, the Boomerang and the Tarantula, e.g

Usage examples of nebulae.

Orders are to proceed to the Draavid nebulae cluster for astrometrical analysis.

As we shall see when we come to the spiral nebulæ, gyratory movements are exceedingly prevalent throughout the universe, and the structure of the Milky Way is everywhere suggestive of them.

In truth, it has troubled some astronomers to explain the luminosity of the bright nebulæ, since it is not to be supposed that matter in so diffuse a state can be incandescent through heat, and phosphorescent light is in itself a mystery.

Milky Way, although a complete ring, is broad and diffuse on one side through one-half its course -- that half alone containing nebulæ -- and relatively narrow and well defined on the opposite side, the author of this singular speculation avers that these facts can best be explained by supposing that the invisible universe consists of two interpenetrating parts, one of which is a chaos of indefinite extent, strewn with stars and nebulous dust, and the other a long, broad but comparatively thin cluster of stars, including the sun as one of its central members.

The dust thrown aside toward the poles of the Milky Way is the substance of the nebulæ which abound there.

Ahead, where the front of the star-plough is clearing the way, the chaos is nearer at hand, and consequently there the rift subtends a broader angle, and is filled with primordial dust, which, having been annexed by the vanguard of the star-swarm, forms the nebulæ seen only in that part of the Milky Way.

They are full of nebulæ and star-clusters, and show striking evidences of spiral movement.

Herschel, since abundantly confirmed, that space is unusually vacant in the immediate neighborhood of condensed star-clusters and nebulæ, which, as far as it goes, might be taken as an indication that the assembled stars had been drawn together by their mutual attractions, and that the tendency to aggregation is still bringing new members toward the cluster.

In and around the Sagittarius region the intermingling of nebulæ and galactic star clouds and clusters is particularly remarkable.

The wonderful aspect of the admixtures of nebulæ and star-clusters in Sagittarius has been described in Chapter 1.

Cygnus, where long, wispy nebulæ, billions of miles in length, some of them looking like tresses streaming in a breeze, lie amid fields of stars which seem related to them.

But the relation is of a most singular kind, for notwithstanding the delicate structure of the long nebulæ they appear to act as barriers, causing the stars to heap themselves on one side.

The stars are two, three, or four times as numerous on one side of the nebulæ as on the other.

These nebulæ, as far as appearance goes, might be likened to rail fences, or thin hedges, against which the wind is driving drifts of powdery snow, which, while scattered plentifully all around, tends to bank itself on the leeward side of the obstruction.

As to dark nebulæ which may possibly lie in the track that the solar system is pursuing at the rate of 375,000,000 miles per year, that is another question -- and they, too, could be dangerous!