5. But if they are exactly in the knots which form the points of intersection between the ascending and descending path of the moon, then the sky will be covered with denser darkness, and the whole atmosphere becomes so thick that we cannot see what is close to us. 6. Again, the sun is conceived to appear double when a cloud is raised higher than usual, which from its proximity to the eternal fires, shines in such a manner that it forms the brightness of a second orb as from a purer mirror. 7. Now let us come to the moon. The moon sustains a clear and visible eclipse when, being at the full, and exactly opposite to the sun, she is distant from his orb one hundred and eighty degrees, that is, is in the seventh sign; and although this happens at every full moon, still there is not always one eclipse. 8. But since she is always nearest to the earth as it revolves, and the most distant from the rest of the other stars, and sometimes exposes itself to the light which strikes it, and sometimes also is partially obscured by the intervention of the shade of night, which comes over it in the form of a cone; and then she is involved in thick darkness, when the sun, being surrounded by the centre of the lowest sphere, cannot illuminate her with his rays, because the mass of the earth is in the way; for opinions agree that the moon has no light of her own. 9. And when she returns to the same sign of the zodiac which the sun occupies, she is obscured (as has been said), her brightness being wholly dimmed, and this is called a conjunction of the moon. 10. Again the moon is said to be new when she has the sun above her with a slight variation from the perpendicular, and then she appears very thin to mankind, even when leaving the sun she reaches the second sign. Then, when she has advanced further, and shines brilliantly with a sort of horned figure, she is said to be crescent shaped; but when she begins to be a long way distant from the sun, and reaches the fourth sign, she gets a greater light, the sun's rays being turned upon her, and then she is of the shape of a semicircle. 11. As she goes on still further, and reaches the fifth sign, she assumes a convex shape, a sort of hump appearing from each side. And when she is exactly opposite the sun, she shines with a full light, having arrived at the seventh sign; and even while she is there, having advanced but a very little further, she begins to diminish, which we call waning; and as she gets older, she resumes the same shapes that she had while increasing. But it is established by unanimous consent that she is never seen to be eclipsed except in the middle of her course.