Book One. The First Conclusion.

The Heavens are Spherical in Shape and Their Motion is Circular.

A large decorative woodcut initial 'C' featuring a scholar or astronomer seated at a desk within a frame of ornate foliage and scrolling patterns.

We are led to establish this through a triple syllogism syllogism: a form of logical reasoning where a conclusion is drawn from two premises: namely, the experimental, the refutational, and the rational. ¶ Indeed, we experience original: "Experimur," meaning to observe or learn through the senses the stars rising, and indeed being gradually elevated until they reach, as it were, the summit of their journey; then they descend step by step to the surface of the horizon. When they reach this point, they soon begin to disappear and remain hidden beneath the earth for some time, and then rise anew and repeat their former course. ¶ Furthermore, the sizes of the stars moved in this way are not found to vary in different locations. From this, no one will doubt that the stars themselves maintain equal distances in their motions from the earth (where the observing eye is close by), and therefore they are moved circularly. ¶ But if you object that the stars seem larger near the horizon than in the middle of the sky, I will indeed admit it; but it is shouted aloud by the study of perspective original: "p̄spectiuis" (perspectivis), referring to the medieval science of optics that the senses are deceived in that matter. Moreover, this kind of circular motion showed itself more clearly in the "always apparent" stars These are circumpolar stars, which never set below the horizon from the observer's location.. For these stars are seen to describe perfect circles, equidistant to one another but of unequal size; their common center, which had not yet been allotted the name of "pole," they conjectured to be immobile. Furthermore, the further the stars are distant from the said center, the larger the circles in which they revolve. They also learned that the stars accustomed to setting possess this property: that the less any one of them is distant from its summit and center, the shorter the delay it suffers beneath the earth. And as they marveled at such a friendly and unvarying revolution of the stars, they conjectured that they were held together in one grand body and carried around by its motion; at that time—as is usual at the beginning of an emerging discipline—no distinction was yet made between the wandering Planets and the fixed stars. Part 1 Finally, they attributed a spherical shape to such a noble body, as it is the most worthy shape and the most accommodating to circular motion.

¶ Furthermore, since we experience the stars rising, moving above the earth, setting, and lingering beneath the earth, and finally repeating their former path, no one is permitted to think that the motion of the heaven is a straight line extending into infinity. For if the stars moved in this way, their distances from the eye would necessarily increase little by little, and they would therefore appear continually smaller until they vanished entirely; this in no way happens. For when stars are carried above the earth, tending toward their disappearance setting, they not only do not appear smaller, but they are even judged larger by the erroneous judgment of the senses. Therefore, no one will deny that the motion of the heavens and stars is circular, and surely no one will doubt that the heaven has a spherical shape. For circular motion is not owed only to a sphere, but to every body that is described by a flat surface led around an axis in motion, such as a round column cylinder, a round pyramid cone, a spheroidal body, and the like. Therefore, if someone estimated that the celestial body carrying the stars around was cylindrical, the circular motion of the stars would not be removed. However, since the celestial spheres are many, wrapped within one another on all sides, and move around different axes (as will be revealed below), if anyone assigned a shape other than spherical to the first heaven, he would either be forced to deny the lower spheres their own motion, or he would have to admit that the celestial bodies suffer a splitting original: "scissionem," referring to a gap or tear in the fabric of the universe, which Aristotelian physics claimed was impossible as nature abhors a vacuum. Since these things are inconsistent, they are not to be admitted by anyone of sound wisdom. Finally, we shall drive an adversary to the same inconsistency if he ascribes any angular shape to the heaven.

¶ Lastly, we shall confirm the proposition by direct reasons. For nature, fleeing any defect, is pleased by the greatest possible utility in all things. Therefore, for the heaven which is to encompass all other things, she impressed the spherical shape, which is the most capacious The sphere is the geometric shape that holds the largest volume relative to its surface area. of all. Also, for the velocity of motion, which is found to be greatest and most regular in this body, it was fitting to choose the spherical shape. For a sphere, moved around its center in any difference of position...