The movements of the superior planets, Mars, Jupiter, Saturn, Uranus, and Neptune, as they appear to us, are different from those of the inferior planets in some important respects. Instead of swinging back and forth east and west of the sun, and never appearing very far away from it, as the inferior planets do, the superior planets make an entire circuit of the heavens, and it is possible to see them at any distance from the sun, and at any time during the night. Sometimes they are, with relation to the earth, in that part of the sky exactly opposite to the sun, and hence in line with it and the earth. At such times they can be seen all night. They are then said to be in opposition, and are in the best position for our observation. The earth being, when in this situation, in a direct line between them and the sun, we have the sun at our backs, as it were, shedding its full rays on the disc of the planet under observation, which is then at its nearest to us, and also at its brightest. For, since the orbits of all the superior planets are outside of ours, the planets never get between us and the sun, and, in consequence, never turn a dark side toward us. Their entire discs are practically always illuminated, and their changes in brightness depend largely upon their changes in distance, which, as we have seen, is not the case with the inferior planets. Mars, the nearest of them, is at times somewhat gibbous (that is, shows a little less than a full face, as the moon does when just beginning to wane), and, in less degree, Jupiter also. But in neither case is this departure from fullness sufficient to have any appreciable effect on the planet’s brightness, and, moreover, it does not occur when the planet is in the most favorable position for us to see it. At opposition, therefore, we always have the full face of the planet presented to us; and being, as we then are, on the same side of the sun with it, we are ninety-three millions of miles (our distance from the sun) nearer to it than the sun is. Being, when in opposition, exactly opposite the sun, the planet rises just as the sun sets. After opposition it rises a little earlier each evening, and is higher up in the sky at each succeeding sunset. When we find it just half-way between the eastern and the western horizon at sunset, it is at quadrature. After quadrature it appears nearer and nearer the western horizon each evening at sunset, until it finally is too near the sun to be visible. It is then traveling in that part of its orbit which is beyond the sun from us. From opposition to this situation it has been an evening star.