Introductory Astronomical Writings of the Ancients

is the same for all; but in our region you would surely call the first the arctic, the second the summer tropic, the third the equator, the fourth the winter tropic, and the fifth the antarctic. But for those who dwell closer to the north than we do, the summer tropic is sometimes counted as the first, the arctic as the second, the equator as the third, the antarctic as the fourth, and the winter circle as the fifth. For since the arctic circle becomes more capacious than the summer tropic, it is necessary that the aforementioned order be observed.

Concerning the power of the parallels.

Indeed, the powers of these same parallels are not the same. For what is considered the summer circle for us is certainly made the winter circle for the Antipodes; conversely, what is the summer circle for them is rendered the winter circle for us. But for those who live under the equator, all three circles are, in their power, clearly summer circles, inasmuch as they dwell under the very orbit of the sun. Although, if they are compared with one another, that which is established for us as the equator holds the place of the summer circle, while both tropics are considered winter circles. For that circle is finally, by nature and by perpetual reasoning, to be called the summer circle in the whole world, which is held to be nearest to the habitation. Whence it happens that for those who live under the equator, the equator itself is established as the summer circle, inasmuch as in it the sun moves above the zenith; but as for the equators