(30) And in periods of seven days the moon undergoes its changes. In the first week she becomes half moon; in the second, full moon; and in the third, in her wane, again half moon; and in the fourth she disappears. Further, as Seleucus the mathematician lays down, she has seven phases. First, from being invisible she becomes crescent-shaped, then half moon, then gibbous and full; and in her wane again gibbous, and in like manner half moon and crescent-shaped.