佛祖歷代通載 1.186

1.186

（四）　月輪者。水珠所成。徑五十由旬。周圍百五十由旬。厚六由旬零十八分。其上復有金銀琉璃玻𭹳珂等。秀成四角。月天子等所居宮殿。是彼日月相去遠近自影增減。由增一分即生上半十五分畢。謂之圓滿。由減一分即生下半自影覆彼十五分畢。曰不圓滿。由增減故名曰宿空。由一晝夜名曰宿地。如是三十名曰一月。

(4) The disc of the moon is made of water jewel (candrakānta). Its diameter is fifty yojanas, its circumference is one hundred and fifty yojanas, and its thickness is six yojanas and eighteen parts [of a yojana]. Upon it are likewise gold, silver, lapis lazuli, crystal, and so forth, elegantly forming four corners, which are the palaces where the moon god and others reside. In accordance with the distance between that sun and moon, its own shadow waxes and wanes. Due to the increase of one part each day, the fifteen parts of the bright fortnight (śuklapakṣa) are born and completed, which is called the full moon. Due to the decrease of one part each day, the dark fortnight (kṛṣṇapakṣa) is born, where its own shadow covers those fifteen parts completely, which is called the waning moon. On account of this waxing and waning, it is called a celestial station (nakṣatra); due to one day and one night, it is called an earthly station. Thirty such stations are called one month.