法苑珠林 4.57

4.57

依立世阿毘曇論云。云何黑半。云何白半。由日黑半。由日白半。日恒逐月行。一一日相近四萬八千八十由旬。日日相離亦復如是。若相近時日日月圓被覆三由旬。又一由旬三分之一。以是事故十五日月被覆則盡。是日黑半圓滿。日日離月亦四萬八千八十由旬。月日日開三由旬。又一由旬三分之一。以是事故十五日月則開淨圓滿。世間則名白半圓滿。日月若最相離行。是時月圓。世間則說白半圓滿。日月若共一處。是名合行。世間則說黑半圓滿。若日隨月後行日光照月光。月光麁故被照生影。此月影還自翳月。是故見月後分不圓。以是事故漸漸掩覆至十五日覆月都盡。隨後行時是名黑半。若日在月前行。日日開淨亦復如是。至十五日具足圓滿。在前行時是名白半。

According to the Lokasthitābhidharma-śāstra: What is the dark half? What is the bright half? Because of the sun there is the dark half, and because of the sun there is the bright half. The sun constantly pursues the moon's movement. Day by day they approach each other by forty-eight thousand and eighty yojanas, and day by day they separate from each other by the same amount. When they approach each other, day by day the moon's disk is obscured by three yojanas and one-third of a yojana. For this reason, on the fifteenth day the moon is completely obscured; this day is the culmination of the dark half. Day by day it separates from the moon also by forty-eight thousand and eighty yojanas, and day by day the moon is unveiled by three yojanas and one-third of a yojana. For this reason, on the fifteenth day the moon is fully unveiled, pure, and complete; in the world this is called the culmination of the bright half. If the sun and moon move at their greatest distance from each other, at that time the moon is full; in the world it is spoken of as the culmination of the bright half. If the sun and moon are together in one place, this is called conjoined movement; in the world it is spoken of as the culmination of the dark half. When the sun moves behind the moon, the sun's light illuminates the moon's light; because the moon's light is coarse, when it is illuminated it casts a shadow, and this moon-shadow in turn conceals the moon itself. Therefore, the back part of the moon is seen not to be round. For this reason, it is gradually veiled until the fifteenth day when the moon is completely veiled; when [the sun] moves behind it, this is called the dark half. If the sun moves ahead of the moon, it is unveiled and purified day by day in the same way, until the fifteenth day when it is fully round; when [the sun] moves ahead of it, this is called the bright half.