BİRİNCİ FEN · İKİNCİ BÂB · YEDİNCİ FASIL · Dördüncü Madde
Fourth Article
Concerning the speed, direction, slowing, and halting of Venus, its bewilderment, its connection with the Sun, and its approach to it.
Know then, esteemed one, that astronomers have stated: The star Venus, like the stars whose characteristics we have described above, sometimes proceeds swiftly, at other times directly, experiencing a slowing in its course and sometimes a return movement. At certain times bewilderment afflicts its movements.
The true cause influencing the occurrence of these differing states is explained as follows: When the star Venus finds itself above the epicycle, the motion of its own center aligns with the motion of the epicycle’s center, as with the rising of the signs. Therefore, the star appears to move with a swift motion exceeding its normal speed. If the star inclines somewhat towards the western side of the epicycle, it is seen moving directly. When Venus descends upon the winter solstice of the epicycle, it moves slowly. For at that time, since it is in descent on its own center, its actual movement becomes imperceptible, and only the motion of the epicycle’s center is visible.
When the star is near the perihelion of the epicycle, its own center's misalignment with the rising of the signs, combined with the motion of the epicycle’s center, which is equal to the movement of the carrying sphere aligned with the rising of the signs (as mentioned in previous articles), causes the star to appear as if it halts, for these two movements are mutually opposed and antagonistic. When the star descends to the lowest point of the epicycle, its own center's motion exceeds that of the epicycle, making the star appear to return. Once the star’s return is complete and the two motions again become equal, the star appears to halt a second time. After this, it seems to move slowly once more.
For at that time, the star’s own center has reached the center of the epicycle, so its movement becomes imperceptible, and only the motion of the epicycle's center is visible. Yet, the star completes its revolution within the epicycle with the same speed, without doubt. For (as previously explained), the movements of the stars and the spheres are similar to one another relative to their own spherical belts, being simple and direct.
The place to which the star returns from its retrograde motion is called the first station; the place to which it moves after its return is called the second station. The completion of Venus’s cycle takes a month and eleven days; the duration of its direct movement is eight and a half months. And this carrying sphere, being inclined about a quarter of a degree towards the south and north directions from the zodiacal belt, and the solstitial points of the epicycle also being inclined, sometimes toward the north and sometimes toward the south, with an approximate difference of two and a half degrees in latitude—it is for these reasons that the star has appeared bewildered in its movements and has therefore been named “bewildered.”
Concerning the instances when Venus approaches the Sun and appears to merge with it: It is explained as follows: The motion of Venus’s carrying sphere is always equal to the motion of the Sun's eccentric sphere, and the center of the epicycle is always tangent to the center of the Sun. In this state, the brilliant star Venus revolves around the sphere of the Sun with the movement of the epicycle, at a distance equal to half the diameter of the epicycle from it; when it reaches the midpoint of those two distances, it appears sometimes as a morning star and sometimes as an evening star, shining like a torch. Sometimes it is illuminated by the Sun, and its own light disappears with that of the Sun.
Unlike other planets, it does not stray far from the Sun’s course [solar disk], but comes close to the Sun twice in each revolution. Once at half its return journey, i.e., at the epicycle's average apogee, proximity and illumination occur. And once in the middle of its return, i.e., when it is located at the winter solstice of the epicycle, a constant state of proximity and conjunction with the Sun takes place. The time elapsed between these two approaches is approximately nine months and twenty days.
The truth lies only with Allah, exalted be He.