俱舍論記 11.59

11.59

「《世施設》中至見不圓滿」者，答。《世施設論》中作如是釋：月被日照發影自覆，於覆暗處遠見不圓。日體淨妙月體稍麁，故月被照發影自覆，如樹發影。照既多少不同，影覆多少為異，所以缺、還不定。

Regarding the passage from "In the Lokaprajñapti" to "it is seen to be incomplete": This is the answer. In the Lokaprajñapti-śāstra it is explained thus: being illuminated by the sun, the moon casts a shadow that covers itself; at the place covered in darkness, seen from afar, it is not round. The substance of the sun is pure and subtle, while the substance of the moon is slightly coarse; therefore, being illuminated, the moon casts a shadow that covers itself, just as a tree casts a shadow. Since illumination differs in degree, the shadow covering it varies in degree; for this reason waning and waxing are not fixed.