Etymologiae, Book III, chapters 35-42: De celeritate caeli to De quattuor partibus caeli
Chapter XXXV. On the speed of heaven The sphere of heaven is said to run with such speed that, were the stars not running against its headlong course to hold it back, it would bring ruin upon the world.
Chapter XXXVI. On the axis of heaven The axis is the straight line of the north that stretches through the middle of the globe of the sphere; and it is called axis because the sphere turns on it like a wheel, or because the Wain is there.
Chapter XXXVII. On the poles of heaven The poles are circles that run around the axis. Of these one is the northern, which never sets and is called Boreus; the other is the southern, which is never seen and is called Austronotius; and they are called poles because they are the circles of the axes, from the use of wagons, named from polire, to polish; but the pole Boreus is always seen and Austronotius never, because the right-hand parts of heaven are higher, while those of the South are pressed down.
Chapter XXXVIII. On the hinges of heaven The hinges of heaven are the extremities of the axis. And they are called hinges (cardines) because heaven turns upon them, or because they revolve like the heart (cor).
Chapter XXXIX. On the convexities of heaven The convexities of heaven are its outermost parts, so called from their curvature, as in the line: “Whenever dewy night shuts in the vault of heaven.” For convex means curved, as if turned or bent, and bowed in the manner of a circle.
Chapter XL. On the gates of heaven. There are two gates of heaven, the east and the west. For the sun comes forth by one gate and withdraws by the other.
Chapter XLI. On the twofold face of heaven The face of heaven, or its head, is the eastern region; its farthest part is the northern. Of this Lucan says: “So lies the lowest part of the world, which the snowy zone and perpetual winters press upon.”
Chapter XLII. On the four parts of heaven The climes of heaven, that is, its regions or parts, are four. Of these the first part is the east, from which some stars rise. The second is the west, where some stars set for us. The third is the north, to which the sun comes in the longer days. The fourth is the south, to which the sun comes in the longer nights. The east (oriens) is named from the rising (exortus) of the sun. The west (occidens), because it makes the day fall (occidere) and perish. For it hides the light from the world and brings darkness over it. The north (septentrio) is named from the seven stars of the axis, which revolve and wheel in it. This is also properly called the vertex, because it is turned (vertitur). The south (meridies) is so called either because the sun there makes the middle of the day, as it were medidies, or because the aether then shines more purely. For pure is called merum. There are also seven other climes of heaven, like seven lines from east to west, under which both men of differing customs and animals of especially diverse kinds are born, and these have been named from certain famous places; of which the first is Meroe, the second Syene, the third Catachoras, that is, Africa, the fourth Rhodes, the fifth the Hellespont, the sixth Mesopontum, the seventh the Borysthenes.