Main star
Tài Yīn
Moon
A chart describes tendencies in a traditional system. It cannot decide health, money, law, marriage or children.
In the classical sources
太陰乃水之精，為田宅主
太陰 is the essence of water and lord of the Property palace.
紫微斗數全書 卷一
About this entry
One palace forward of 天府, 太陰 is the first of the stars counted in that direction. It can meet 太陽 in the same palace at 丑 and 未. The table marks 亥, 子 and 丑 temple and 卯, 辰 and 巳 fallen, with 午 and 未 a step above that.
Moonlight organizes everything the book says here. The star is the partner of the sun and its measure is waxing and waning, with 上弦 and 下弦 named as the first and last quarters. The passage attributed to 希夷先生 calls 酉 through 丑 its proper ground and 卯 through 未 its fallen ground, which lines up closely with the table. The book treats it as the mother's star in a chart and describes an intelligent, gentle temperament.
Light again decides how the text reads it, and companions add to that: 天同 at 子 and 午, 太陽 at 丑 and 未, 天機 at 寅 and 申. It takes 化祿 in 丁 years, 化權 in 戊, 化科 in 癸 and 化忌 in 乙. In 庚 years the Wikisource text gives it 化科 as well, and the calculator uses that row.
Where this text comes from
The Chinese follows the Wikisource text of 紫微斗數全書, whose base edition the page does not state. Statements about the calculator describe its own rules, and modern readings are labeled as modern.
The English name and the wording here are our own. Quotations keep the stored text of the witness.