THEORICA

When the final declination has been determined, the declination of any degree placed in that oblique circle will be known, and that which ascends with that degree upon the horizon of the equinoctial circle will also be known. And it has been declared there that the ascensions of the entire quarter of the quarters of the oblique circle, comprised between the two equinoctial points and the two solstitial points, are equal to the ascensions of the entire quarter placed on the face of the equinoctial circle, though they differ in the degrees of ascension in the lesser degrees of the circle's quarter. Sometimes the ascensions exceed, and sometimes they are smaller; we will direct ourselves to this in its proper place, God willing.

Since the space of the motion of the fixed stars is found to be different in observation according to the diversity of times—for sometimes this motion is found to be slow with a small retardation, sometimes with a greater retardation, sometimes following the order of the signs, and sometimes against the order of the signs—and since this pertains to the part of the universal motion, and since at times, over a great space of time, the motion is not perceived by the observations of the men of that age: for the most part, [the reason] they recognized the motion of the fixed stars was when they saw their declination in latitude, when they observed them to be on the equinoctial i.e., the celestial equator. That is, they considered a fixed star existing upon the equinoctial to be removed from it, and that stars which had been northern from the equinoctial in the past had become southern, and those which had been southern had become northern from their prior place. Therefore, they determined that this motion occurs upon an oblique circle. And because this motion returns with this declination of theirs, they judged that this oblique orbit moving them moves this sphere against the motion of the supreme the primum mobile or prime mover.

And because the seven planets are diverse in the motion of longitude with great diversity, yet the diversity in latitude is small, they therefore posited that the motion of all of them together follows this oblique orbit regarding the diverse motion, and upon its poles only. And when the orbit of the fixed stars is oblique according to them, I do not know why they imagine it to follow another, superior orbit without stars, for it would suffice for them to posit the oblique one itself, and there is no need to labor to posit another, superior one. Furthermore, why did they not posit this oblique orbit moving these spheres upon their own poles with a motion different from the motion of the supreme—that is, the universal [motion]—having a position opposite to the position of the supreme, so that it might be beneath the orbit of the moon? For they have no proof from astronomy itself that it is beneath the supreme and above all others, and it would be more probable to reason that it is beneath the orbit of the moon, since it first moves the orbit of the moon with that motion beginning from the fact that the orbit of the moon is the swiftest of all orbits with this diverse motion when it is near its mover; and for this reason, the one closer to the moon is swifter than that which is more remote. Therefore, the orbit of the fixed stars is the slowest of all, and that motion proceeds in a straight order.

Furthermore, why did they not attribute the eccentricity of all of these to this oblique orbit alone, and the diversity of these orbits in velocity and slowness would be attributed to the eccentricity of the oblique circle and its motion of the orbits upon itself? Yet they concede and confess with this the distinction of each of the orbits and the division of them into parts, some of which differ from another in motion, with the communication and mixture of them with one another, and in motion and substance.

BUT because the ancients did not truly possess this motion of the fixed stars which they established, therefore there were many doubts and entanglements concerning the truth of their motion. For predecessors like Hermes and those after him who give themselves to images likely referring to astrological image magic say that these stars have a motion sometimes according to the order of the signs and sometimes against it, as if this were a thing known to them per se, or handed down from their ancestors. And when later [astronomers] came, such as the Chaldeans, and those who found the motion of these stars before the age of Bactenzar often associated with the astronomer Al-Battani or related historical figures, in order to demonstrate the truth of what the predecessors discovered, they did not find this motion for them, and they abandoned that motion said by the early ancients, for they did not establish a calculation for them.