If a large, solid ball is hung up in the air, with bright sunlight shining on it, the sunlight will cast a _cone of shadow_ behind the ball. It will throw, in a direction just away from the sun, a long, round shadow, the same as the ball at first, but tapering gradually off to a point. If the ball is near the ground, a round shadow will rest there, almost as large as the ball. The higher the ball is placed, the smaller will be the round shadow, till at length, if the ball be taken far enough upwards, the shadow will not reach the ground at all. Our earth and all the planets cast just such tapering cones of dark shadow behind them into space. The cone always lies in a direction away from the sun. It is when the moon comes into this shadow that an “eclipse of the moon” takes place. Sometimes she only dips half-way into it, or just grazes along the edge of it, and that is called a “partial eclipse.” Sometimes she goes in altogether, straight through the midst of the shadow, so that the whole of her bright face for a short time grows quite dark. Then we have a “total lunar eclipse.” CHAPTER XV. YET MORE ABOUT THE MOON. There are two ways of thinking about the moon. One way is to consider her as merely the earth’s attendant satellite. The other way is to consider her as our sister-planet, traveling with us round the central sun. The first is the more common view; but the second is just as true as the first. For the sun does actually pull the moon towards himself, with a very much stronger pulling than that of the earth. The attraction of the sun for the moon is more than double the attraction of the earth for the moon. If it were not that he pulls the earth quite as hard as he pulls the moon, he would soon overpower the earth’s attraction, and drag the moon away from us altogether. People are often puzzled about the orbit or pathway of the moon through the heavens. For in one sense they have to think of her as traveling round and round in a fixed orbit, with the earth in the center. In another sense they have to think of her as always journeying onwards with the earth in her journey round the sun, and thus never returning to the same point. There are two ways of meeting this difficulty. First of all, remember that the one movement does not interfere with the other. Just as in the case of the earth traveling round the sun, and also traveling onward with him through space; just as in the case of a boy walking round and round a mast, and also being borne onwards by the moving vessel,--so it is here. The two movements are quite separate and independent of each other. As regards the earth alone, the moon journeys round and round perpetually, not in a circle, but in a pathway which comes near being an ellipse. As regards the actual _line_ which the moon’s movements may be supposed to draw in space, it has nothing elliptical about it, since no one point of it is ever reached a second time by the moon.