BİRİNCİ FEN · İKİNCİ BÂB · YEDİNCİ FASIL · Üçüncü Madde
Article Three
It describes the epicycle of the planet Venus, along with its form and movement.
O Noble One! Know that astronomical scholars, in explaining and detailing the conditions of this planet Venus, do not suffice with the quantities described concerning the states of the aforementioned three high spheres (the triple highest), but have posited an additional small sphere encompassing the earth and named it the epicycle.
The epicycle is a small sphere, not encompassing the earth, within the sphere of common eccentricity which carries this planet itself. It remains fixed upon the belt of the second inclined sphere, which is inclusive of the earth and eccentric. The diameter of the epicycle is tangent to and equal on both surfaces of the carrying sphere. And this epicycle is a solid, spherical body enclosed by a surface. Upon the body of the inclined sphere, it rotates around its own center with a movement unique to itself, from west to east, as is the rising of the constellations, carrying Venus, which remains fixed on one side, along with it. The epicycle moves Venus, rotating it around its own center, more than half a degree beyond three hundred and sixty degrees within a day and night upon its belt.
Proceeding in this manner, it completes its cycle approximately every nineteen and a half months. This movement is what they call the star’s peculiar motion or the star's specific movement.
The planet Venus is also a solid, spherical body, filled with light. It is embedded within the body of the epicycle, such that the surface of the star [49/a] is tangent to the surface of the epicycle at a common point beside its two poles and belt, on one side. That is to say, the planet Venus is entirely upon the body of the epicycle, with its surface touching its surface. Just as the carrier moves, it has been newly observed and witnessed through astronomical observation that the planet Venus also rotates around its own center by means of its specific movement, according to the rising of the constellations, carried by the epicycle, as explained above for the epicycle’s movement.