These two simple movements of the planets--that around the sun and that on their axes--are their principal real movements, and are such as they would show to be if seen from the sun, which is the center of them. There are also certain minor real movements arising from various causes, one being the influence that the planets exercise on one another; but for the ordinary observer these have no particular significance. Then, the planets all share the one grand movement which the sun itself is known to be making through limitless space to a destination of which we are in utter ignorance, over even a path which we know nothing of save that it leads toward the bright star Vega, in the constellation of the Lyre. As the sun moves on in that direction at the rate of eleven miles a second he takes with him all his family of planets and planetoids, with their satellites, and whatever other bodies have their abode in his domain. Thus they travel as a body, each individual spinning on its axis, from the sun itself down to the smallest planetoid, the satellites circling around the planets, and the planets in their turn around the sun. And in all these movements the earth takes part as one of the planets. The sun itself is following a comparatively straight line in space, and, so far as we know, in allegiance to no other body. It is, though, just possible that this comparatively straight line may be the arc of a circle so vast that we have not yet had time to discover its curvature, and that the sun itself may be pursuing its own circuit around some still more powerful body. VII HOW THE INFERIOR PLANETS SEEM TO MOVE Of the real movements of the planets, as described in the last chapter, we get here on the earth only a very fragmentary view. Without the aid of the telescope none of them is visible to us except the movements in their orbits, and these, to our view, are somewhat different from the simple, circling course apparent to an observer on the sun. The difference is due to the fact that the earth itself is always in movement in just the same way that the other planets are, and we, being never at any time at the center of the orbits, do not see the movements of the planets as they truly take place, but only as they are outlined against the sky. So the appearances and disappearances and visible travels among the stars by which we know the planets are only as we see them. Some knowledge of the real movements is necessary to a proper understanding of the apparent movements; but it is only with the latter that, for ordinary observation, we need to be particularly acquainted.