1. There are five zones in the heavens, according to the differences
of which certain parts of the earth are inhabitable, because of their
moderate temperature, and certain parts are uninhabitable because of
extremes of heat and cold. And these are called zones or circles for
the reason that they exist on the circumference of the sphere.
2. The first of these circles is called the Arctic, because the
constellations of the Arcti are visible enclosed within it; the
second is called the summer tropic, because in this circle the sun
makes summer in northern regions, and does not pass beyond it but
immediately returns, and from this it is called tropic.
3. The third circle is called ἰσημερινὸς, which is equivalent to
_equinoctialis_ in Latin, for the reason that when the sun comes to
this circle it makes equal day and night (for ἰσημερινὸς means in
Latin day equal to the night) and by this circle the sphere is seen
to be equally divided. The fourth circle is called Antarctic,[271]
for the reason that it is opposite to the circle which we call Arctic.
[271] This order is repeated in 13, 6.
4. The fifth circle is called the winter tropic (χειμερινὸς
τροπικός), which in the Latin is _hiemalis_ or _brumalis_, because
when the sun comes to this circle it makes winter for those who are
in the north and summer for those who dwell in the parts of the
south.