Etymologiae, Book III, chapters 28-34: De astronomiae ratione to De eiusdem sphaerae cursu
Chapter XXVIII. On the reckoning of astronomy The reckoning of astronomy consists in very many ways. For it defines what the world is, what the heaven is, what is the position and course of the sphere, what the axis of the heaven and the poles are, what the climates of heaven are, what the courses of the sun and moon and stars are, and so on.
Chapter XXIX. On the world and its name The world (mundus) is that which consists of heaven, and earth and sea and all the stars. It was so called because it is always in motion (motus); for no rest is granted to its elements.
Chapter XXX. On the form of the world The form of the world is shown thus. For as the world rises toward the northern region, so it declines toward the southern.
Its head, and as it were its face, is the eastern region, the last part is the northern.
Chapter XXXI. On heaven and its name The philosophers have said that heaven is round, revolving and fiery; and it is called by this name (caelum) because, like an engraved (caelatum) vessel, it has the signs of the stars impressed. For God marked it out with bright lights, and filled it with the sun and the shining orb of the moon, and adorned it with the splendid signs of the twinkling stars. In Greek it is called ouranos from horasthai, that is, from seeing, because the air is clear and purer for gazing.
Chapter XXXII. On the position of the celestial sphere The sphere of heaven is a kind of form shaped in a round, whose centre is the earth, enclosed equally on all sides. They say this sphere has neither beginning nor end, because in a round, like a circle, it is not easy to grasp where it begins or where it ends. The philosophers introduced seven heavens of the world, that is, the planets, with the concordant motion of their globes, to whose orbits they recall that all things are connected, which they think turn back, bound to them and as it were inserted in them, and are borne by motion in the contrary direction to the rest.
Chapter XXXIII. On the motion of the same sphere The sphere’s motion is turned on two axes, of which one is northern, which never sets and is called the Boreal; the other southern, which is never seen, and is called Austronotian. On these two poles they say the sphere of heaven moves, and with its motion the stars fixed in it circle from the east to the west, the northern ones making shorter circuits near the pivot.
Chapter XXXIV. On the course of the same sphere The sphere of heaven turns from east and west once in a day and night in the space of twenty-four hours, in which the sun by its revolution completes its course over the lands and under the lands.