Introductory Astronomical Writings of the Ancients

For all parallel circles are bisected by the horizon.

Concerning the dimension of the five parallel circles.

The distances of the circles from one another do not remain the same throughout the entire inhabited world; rather, for the mapping of the spheres, they are divided in this way: the entire meridian circle being divided into sixty parts, the arctic circle is mapped at a distance of six parts from the pole. The same circle is mapped in the other direction from the summer tropic at a distance of five parts. The equator is at a distance of twenty-four parts from either tropic. The winter tropic circle is at a distance of five parts from the antarctic. And the antarctic is at a distance of six parts from the pole. In every region and city, the circles do not have the same distances from one another; rather, the tropics maintain the same distance from the equator in every climate. But the tropic circles do not have the same distance from the arctic circles across all horizons; rather, some are at a smaller interval, and some are at a greater one. Similarly, the arctic circles do not have an equal distance from the poles in every climate, but some have a smaller, and others a greater, distance. All spheres, however, are mapped according to the horizon in Greece.

Concerning the colure circles.

There are also circles through the poles, called by some "colures," to which it happens that they contain the poles of the world within their own circumferences. Colures