Preface

Our predecessors introduced a multitude of celestial spheres to preserve the apparent motion of the stars within a regular system.

It seemed highly absurd that a celestial body, being the most perfectly round, would not always move uniformly.

However, they realized that through the combination and interaction of regular motions, a body could appear to move in different ways relative to a given position.

Callippus and Eudoxus tried to explain this using concentric circles.

But concentricity could not support:

• the apparent revolutions of the stars
• their observed rise and fall

Therefore, the preferred theory became one involving eccentrics and epicycles proposed by Ptolemy and many others. It eventually gained widespread acceptance among scholars.

It was mathematically accurate, but still left room for doubt.

Their models were not sufficient unless they also introduced certain imaginary “equants” which showed that a celestial body does not always move with uniform speed either in its deferent orbit or around its own center.

Because of this, such a theory did not seem entirely satisfactory or fully aligned with rational principles.

1 Callipus de Cyzico, astronomus Graecus, floruit ca. 330 a. Chr. n. 2 Eudoxus de Cnido (391 - 338 a. Chr. n.), astronomus Graecus. 3 Hypothesis Apollonii de Perga (floruit ca. 210 a. Chr. n.) 4 Ptolemaeus (ca. 100 - ca. 170), astronomus Graecus.