Introductory Astronomical Writings of the Ancients

all parallel circles are, as it were, bisected into equal parts by the horizon.

But the intervals of the circles are not fixed among themselves throughout the whole globe; rather, they are wont to be arranged according to this method for the description of the spheres. When any meridian circle is divided into sixty parts, the arctic circle is described at an interval of six of those sixty parts from the pole. The same is marked at an interval of five of those sixty parts from the summer solstice circle in the other direction. The equator is distant from each of the tropics by twenty-four of those sixty parts. The winter circle is distant from the antarctic by five of those sixty parts. The antarctic is distant from the pole by six of those sixty parts. However, they do not maintain the same distance between themselves in every region or city; rather, the tropics claim an equal distance from the equator in every inclination. But the same are not at an equal distance from the arctic circles across all horizons, but are sometimes smaller, sometimes larger. Thus, finally, the arctic poles also do not maintain an equal distance in every inclination, but have it sometimes larger, sometimes smaller. All spheres, however, are described according to the horizon of Greece.

There are also circles drawn through the poles, which some call colures. It happens to them that they receive the poles of the world into their circuits. The colures, however