Fig. 3.—An Elongated Irregular Nebula.
According to Sir Robert Stawell Ball, the nebula in Orion ([Fig. 1]), one of the most beautiful objects revealed by the telescope, covers an area more than a million times larger than that occupied by our entire solar system. Many of the nebulæ are of the spiral form, which shows their whirling motion. To the astronomer, the Great Spiral Nebula ([Fig. 2]) represents a mighty sun and system of planets in process of formation. [Fig. 3] shows an elongated, irregular nebula, from the Constellation Cygnus. This sketchy streak of nebulous material, although it is still many millions of miles wide, is but the remaining thread of a once mighty nebula that has condensed and is still condensing into the surrounding stars.
The nebulæ represent various stages of evolution into suns and worlds. Some resemble great clouds of rarified matter; some are distinctly spiral in form; some show advanced condensation into stars with attendant planetary systems. The stars, too, exhibit various degrees of progress from their birth in the nebula. Some are white, which shows that they are young; some are yellow, which indicates that they have reached middle age; some are red, which is the mark of their declining years.
Fig. 4.—Lunar Craters: Hyginus and Albategnius.
So the stars, the glowing suns, grow old and die, and, lifeless, wheel in space, like mighty cinders cold and dark, reflecting, like the moon, the light that shines on them from brilliant orbs.
The moon ([Fig. 4]) is a dead star. Its light and heat are gone. It wheels in space, an extinct cinder, and by the borrowed light which enables us to see the craters on its surface, it prophesies for us the fate that one day will overtake the earth. But that will be millions of years from now; so we need not worry!
But how is the nebula formed? The cluster in the constellation Hercules ([Fig. 5]), if it is not in fact a colossal nebula, shows that some of the stars are very close together. Now, these immense objects, that in blind fury dash through space, may come into collision with one another and explode into a nebulous cloud; or they may plough through dense swarms of meteorites, with a resultant explosion on a smaller scale; or, torn by internal convulsions, they may burst into fragments and scatter their dead dust over the abyss of space. In one or all of these ways the nebula is born, to begin again the recurring cycle of Nature’s life.
Fig. 5.—The Cluster in Hercules.