Venus

Venus has a system of circles similar to those of the superior planets, but with different characteristics of motion. The orbit, along with its larger epicycle, completes equal revolutions in nine months, as previously mentioned.

Through this combined motion, the smaller epicycle is consistently aligned with the firmament, establishing its greatest apse at the point where we have stated that the Sun is directed.

However, the smaller epicycle, completing unequal revolutions relative to these, maintains an irregularity in its motion with respect to the great orbit. With respect to this revolution, it completes exactly two full circuits, so that whenever the Earth is aligned along the diameter extending to the apse, the planet is then nearest to the center of the larger epicycle, and in the transverse quadrants, it is at its farthest distance—somewhat similarly to how the smaller epicycle of the Moon aligns with the Sun.

The proportion between the semi-diameter of the great orbit and that of Venus is 25 to 18. The larger epicycle takes up three-quarters of one unit, while the smaller one takes up one-quarter. Venus, like the superior planets, is also observed to retrograde, most notably when it is closest to the Earth. This occurs in a way similar to the superior planets but in reverse: in those, retrograde motion occurs because the Earth’s movement overtakes them, whereas in Venus, it is because the Earth is overtaken. Also, whereas in the superior planets, the Earth’s orbit is contained within theirs, in Venus, it is the containing orbit.

Therefore, Venus is never in opposition to the Sun, since the Earth can never be positioned in between them. Instead, Venus appears to turn back at specific distances from the Sun, determined by the tangential lines that extend from the Earth’s center to the orbit’s circumference. In our view, Venus never exceeds 48 degrees from the Sun. This, then, is the overall nature of Venus’ motion in terms of its longitudinal path.

Venus also deviates in latitude for two reasons. First, its orbital axis is inclined by two degrees, and second, it has its node, from which it begins its northern ascent, located at its apse. The deviation that results from this inclination is fundamentally the same but appears twofold to us. When the Earth happens to be at one of Venus’ nodes, it is seen moving upward or downward in a transverse manner—this phenomenon is called a reflection. These appear to be natural obliquities of the orbit and are called declinations, which are especially evident in the quadrants. Elsewhere, both latitudinal deviations intermingle, with one surpassing and overpowering the other, so that through similarity or dissimilarity, they mutually enhance or cancel each other out.

This axial inclination also undergoes a mobile libration, though unlike that of the superior planets, which is fixed relative to the nodes, this libration occurs around certain other moving points, completing annual revolutions relative to the planet. As a result, whenever the Earth stands opposite to Venus’ apse, the greatest flexion of the libration occurs, and this is seen in Venus itself, regardless of where it happens to be in its orbit.

Therefore, if Venus is at its apse or diametrically opposite to it, it will not be entirely devoid of latitude, even if it happens to be at its nodes at that moment. As this flexion decreases, until the Earth moves one quadrant away in its orbit, and until the point of greatest deviation moves away from Venus by the same amount, no trace of this deviation can be detected. Then, with the continuous movement of the libration and as this motion shifts from north to south (or vice versa), Venus is drawn toward the part of its orbit that was previously southern but has now, due to its opposition, become northern. This continues until the cycle completes its full circle and the greatest deviation reaches its peak once again, equal to the first.

Thus, in the same way, this process extends through the other half of the circle, maintaining a structured pattern. Consequently, this meridional latitude—which is often called deviation—never remains fixed but is instead produced by two concentric orbits with oblique axes. Just as we explained for the superior planets, the same principle applies here as well.