A lamp shines by its own light; but a looking-glass, set in the sun’s rays and flashing beams in all directions, shines by reflected light. In a dark room it would be dark. If there were no sun to shine upon Mars or Venus, we should see no brightness in them. The moon is like the planets in this. She has only borrowed light to give, and none of her own. Any one of the planets removed to the distance of the nearest fixed star, would be invisible to us. Reflected light will not shine nearly so far as the direct light of a burning body. There may be thousands or millions of planets circling round the stars--those great and distant suns--just as our brother-planets circle round our sun. But it is impossible for us to see them. The planets which we can see are close neighbors, compared with the stars. I do not mean that they are near in the sense in which we speak of nearness upon earth. They are only near in comparison with what is so very much farther away. For a while we must now leave alone all thought of the distant stars, and try to gain a clear idea of the chief members of our own Family Circle--that family circle of which the sun is the head, the center, the source of life and warmth and light. There are two ways in which astronomers group the planets of the Solar System. One way is to divide them into the Inferior Planets, and the Superior Planets. As the earth travels in her pathway round the sun, two planets travel on their pathways round the sun nearer to him than ourselves. If the pathway or orbit of our earth were pictured by a hoop laid upon the table, with a ball in the center for the sun; then those two planets would have two smaller hoops of different sizes _within_ ours; and the rest would have larger hoops of different sizes _outside_ ours. The two within are called inferior planets, and the rest outside are called superior planets. A round hoop would not make a good picture of an orbit. For the yearly pathway of our earth is not in shape perfectly round, but slightly oval; and the sun is not exactly in the center, but a little to one side of the center. This is more or less the case with the orbits of all the planets. But the laying of the hoops upon the table would give no bad idea of the way in which the orbits really lie in the heavens. The orbits of all the chief planets do not slope and slant round the sun in all manner of directions. They are placed almost in the same _plane_ as it is called--or, as we might say, in the same _flat_. In these orbits the planets all travel round in the same direction. One may overtake a second on a neighboring orbit, and get ahead of him, but one planet never goes back to meet another.