Let us consider, just for a moment, and in a very simple manner, the universe in which man lives. And let us start with what we know, and keep well within those lines. First of all, then, as to the earth itself: Thanks to the knowledge man now has respecting the earth it is no longer regarded as the center of the universe, around which revolve sun and moon and stars, that in the ages of darkness were thought to have been created for the sole purpose of giving light by day and by night to the earth. No; man has learned the true relation of the earth to these other objects in the universe. He knows that the earth is but one of a number of planets--one of a group of eight major planets, and a larger number of minor ones, that revolve regularly around the sun--and one of the smallest of the group of major planets at that. Outside of this group of planets, with whose motions and laws man has become familiar, is a vast host of what are called "fixed stars;" that is, stars that apparently have no motion, but which really do move, only their orbits are so immense that man with the unaided eye can not discern their movements--hence we call them "fixed stars."[A] Our astronomers have learned that these "fixed stars" are not like the planets which move in their orbits about our sun, but, on the contrary, are like the sun itself, self-luminous bodies, and doubtless like the sun the center of opaque planetary groups; or at least we may say that reasoning from analogy, that is regarded as a very probable fact. [Footnote A: "To the unassisted eye, the stars seem to preserve the same relative positions in the celestial sphere generation after generation. If Job, Hipparchus, or Ptolemy should again look upon the heavens, he would, to all appearance see Aldebaran, Orion, and the Pleiades exactly as he saw them thousands of years ago, without a single star being moved from its place. But the refined methods of modern astronomy, in which the telescope is brought in to measure spaces absolutely invisible to the eye, have shown that this seeming unchangeability is not real, but that the stars are actually in motion, only the rate of change is so slow that the eye would not, in most cases, notice it for thousands of years. In ten thousand years, quite a number of stars, especially the brighter ones, would be seen to have moved, while it would take a hundred thousand years to introduce a very noticeable change in the aspect of the constellations." (Newcomb's Astronomy, pp. 464-5.)] Sir Robert Ball in speaking of these worlds and the probability of their being inhabited says: