P172:3, 15:6.1 Irrespective of origin, the various spheres of space are classifiable into the following major divisions:
P172:10, 15:6.3 The Suns. These are the stars of space in all their various stages of existence. Some are solitary evolving space systems; others are double stars, contracting or disappearing planetary systems. The stars of space exist in no less than a thousand different states and stages. You are familiar with suns that emit light accompanied by heat; but there are also suns which shine without heat.
P172:11, 15:6.4 The trillions upon trillions of years that an ordinary sun will continue to give out heat and light well illustrates the vast store of energy which each unit of matter contains. The actual energy stored in these invisible particles of physical matter is well-nigh unimaginable. And this energy becomes almost wholly available as light when subjected to the tremendous heat pressure and the associated energy activities which prevail in the interior of the blazing suns. Still other conditions enable these suns to transform and send forth much of the energy of space which comes their way in the established space circuits. Many phases of physical energy and all forms of matter are attracted to, and subsequently distributed by, the solar dynamos. In this way the suns serve as local accelerators of energy circulation, acting as automatic power-control stations.
P172:12, 15:6.5 The superuniverse of Orvonton is illuminated and warmed by more than ten trillion blazing suns. These suns are the stars of your observable astronomic system. More than two trillion are too distant and too small ever to be seen from Urantia. But in the master universe there are as many suns as there are glasses of water in the oceans of your world.
P173:1, 15:6.6 The Dark Islands of Space. These are the dead suns and other large aggregations of matter devoid of light and heat. The dark islands are sometimes enormous in mass and exert a powerful influence in universe equilibrium and energy manipulation. The density of some of these large masses is well-nigh unbelievable. And this great concentration of mass enables these dark islands to function as powerful balance wheels, holding large neighboring systems in effective leash. They hold the gravity balance of power in many constellations; many physical systems which would otherwise speedily dive to destruction in near-by suns are held securely in the gravity grasp of these guardian dark islands. It is because of this function that we can locate them accurately. We have measured the gravity pull of the luminous bodies, and we can therefore calculate the exact size and location of the dark islands of space which so effectively function to hold a given system steady in its course.
P173:2, 15:6.7 Minor Space Bodies. The meteors and other small particles of matter circulating and evolving in space constitute an enormous aggregate of energy and material substance.
P173:3, 15:6.8 Many comets are unestablished wild offspring of the solar mother wheels, which are being gradually brought under control of the central governing sun. Comets also have numerous other origins. A comet's tail points away from the attracting body or sun because of the electrical reaction of its highly expanded gases and because of the actual pressure of light and other energies emanating from the sun. This phenomenon constitutes one of the positive proofs of the reality of light and its associated energies; it demonstrates that light has weight. Light is a real substance, not simply waves of hypothetical ether.
P173:4, 15:6.9 The Planets. These are the larger aggregations of matter which follow an orbit around a sun or some other space body; they range in size from planetesimals to enormous gaseous, liquid, or solid spheres. The cold worlds which have been built up by the assemblage of floating space material, when they happen to be in proper relation to a near-by sun, are the more ideal planets to harbor intelligent inhabitants. The dead suns are not, as a rule, suited to life; they are usually too far away from a living, blazing sun, and further, they are altogether too massive; gravity is tremendous at the surface.
P173:5, 15:6.10 In your superuniverse not one cool planet in forty is habitable by beings of your order. And, of course, the superheated suns and the frigid outlying worlds are unfit to harbor higher life. In your solar system only three planets are at present suited to harbor life. Urantia, in size, density, and location, is in many respects ideal for human habitation.
P173:6, 15:6.11 The laws of physical-energy behavior are basically universal, but local influences have much to do with the physical conditions which prevail on individual planets and in local systems. An almost endless variety of creature life and other living manifestations characterizes the countless worlds of space. There are, however, certain points of similarity in a group of worlds associated in a given system, while there also is a universe pattern of intelligent life. There are physical relationships among those planetary systems which belong to the same physical circuit, and which closely follow each other in the endless swing around the circle of universes.