Know, may God help you, that the moon is an isthmus position between what is called the crescent and what is called the full moon in the case of increasing and decreasing light, so it is called a crescent because of the loudness of the voices when it is seen at both ends, and it is called a full moon in the case of the generality of light for itself in the eye of the beholder, and what remains for the moon is a position except what is between these two terms, except that its full moon. In its concealment from the perception of sight under the ray of the sun that prevents sight from it, it is called right, and it is from the side that follows the sun a full moon, just as it is in the case of our being a full moon. It is from the side in which the sun does not appear right, and what is between these two positions is in proportion. Whatever light appears in it decreases on the other side, and to the extent that it is hidden from one side, it appears with light from the other side, du