The moon is never visible, until it is twelve degrees from the sun, because the brightness of the light of the sun prevents us seeing it. And it is twelve degrees from the sun when it appears facing us in the beginning and then it is at its prime, i.e., at its first light. And the sun sets in regard to the inhabitants of the east of the world when the moon is eleven degrees from it before it is seen, while to the inhabitants of the west of the world it is shining clearly, when the moon is twelve degrees or more from the sun. Therefore the inhabitants of the west of the world see the moon sooner than the inhabitants of the east by one day. Consequently when the moon is twelve or thirteen degrees from the
p.107sun, or a little more, the visible size of it is small, and when it is from eighteen to twenty-three degrees from the sun then its size is greatest.