Page:The Music of the Spheres.djvu/194

 lect in great clouds which, when far from the light of stars, are dark. When the accumulating clouds of dust become so heavy that gravitation begins to draw their particles together, heat is generated and the mass begins to glow, although sometimes dark masses, if they are close to stars, will glow with reflected starlight. The gaseous clouds are devoid of solid or liquid matter, and consist, the spectroscope shows, of glowing gases, apparently nebulium and hydrogen. Thus the Nebula of Orion, which is a gaseous nebula, is never spoken of as a "universe," like the Nebula of Andromeda, which may be resolved into stars.

The finest example of an irregular nebula is the Nebula of Orion; of a ring nebula, that found in the constellation of Lyra; and of a spiral nebula, the one found in the constellation of Canes Venatici, just below the handle of the Big Dipper. The spiral of Andromeda, which is turned edgewise to the earth, is the largest nebula in the sky.

Canis Major, the "Great Dog" of Orion, lies in a straight line southeast of his Belt Stars. Canis Minor, his "Small Dog," lies across the Milky Way, 20 degrees northeast of Betelgeuse, the pink star on his shoulder. The three stars form a large and easily traced triangle.

Canis Minor is usually pictured as a Spaniel standing on the bank of the Milky Way and gazing across its river of stars at the giant Orion with his club upraised against the Bull. Although this dog is usually said to be Orion's dog, it is sometimes claimed to be one of Diana's hounds that followed her in the hunt. Other legends claim that Canis Minor was the dog of Icarus who discovered the slaying of his master by the shepherds of Attica and for this was placed among the stars. Procyon, the brightest star