Chapter 44. On the five circles of the heavens.
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.
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.
Chapter 47. On the size of the sun.
1. The size of the sun is greater than that of the earth and so from the moment when it rises it appears equally to east and west at the same time.[272] And as to its appearing to us about a cubit in width, it is necessary to reflect how far the sun is from the earth, which distance causes it to seem small to us.
Chapter 48. On the size of the moon.
1. The size of the moon also is said to be less than that of the sun. For since the sun is higher than the moon and still appears to us larger than the moon, if it should approach near to us it would be plainly seen to be much larger than the moon. Just as the sun is larger than the earth, so the earth is in some degree larger than the moon.
Chapter 49. On the nature of the sun.