What is Purple Star Astrology (Zi Wei Dou Shu)?

Where the book says it comes from

The book opens with a preface signed by Luo Hongxian (羅洪先). He writes that on a visit to Mount Hua, to the shrine of Master Xiyi (Xiyi Gong, 希夷公), a Daoist showed him this book as Master Xiyi’s:

“It is the collected Zi Wei Dou Shu of Master Xiyi.” … From the changes of the stars, one knows the good and ill of a person’s life.

希夷公紫微斗數集也。……即星辰之變化，而知人命之休咎

The preface (Luo Xu, 羅序). This is the book’s own account; this site makes no further claim about who wrote it or when. The text

How a chart is built

1. The moment of birth, turned into a lunar year, month and day and one of twelve two-hour periods (Shi Chen, 时辰), by true solar time at the birthplace, not the clock. True solar time
2. Twelve palaces. The birth month and two-hour period fix the Self palace (Ming Gong, 命宫), and the other eleven follow around the chart: Self, Siblings, Spouse, Children, Wealth, Health, Travel, Friends, Career, Property, Wellbeing, Parents.
3. Fourteen main stars. The Emperor’s position is found first and the others follow from it: The Emperor, The Strategist, The Sun, The Iron, The Blessing, The Mystic, The Treasury, The Moon, The Wolf, The Voice, The Minister, The Elder, The General, The Disruptor.
4. Four transformations (Si Hua, 四化). The stem of the birth year turns four stars into Fortune, Power, Merit and Trouble.
5. Decades (Da Xian, 大限). From the Self palace, each ten years of life moves to the next palace.

The book’s opening rhapsody (Tai Wei Fu, 太微賦) puts it this way:

The stars are spread through twelve walls and the reckoning fixed at thirty-six positions: well placed is the rare thing, out of measure is empty. Broadly the Self and the Body are the root of blessing, with the root source as the means of straitness and passage.

其星分布一十二垣，數定乎三十六位，入廟為奇，失度為虛，大抵以身命為福德之本，加以根源為窮通之資。

What the book says a chart shows

The dipper reckoning is deep and subtle and its reasoning hard to make plain; and though a hundred chapters are set out in question and answer, there is still what is said and not exhausted. As for the stars' divisions of the field, each has what it belongs to — long life or short, worth or folly, wealth and rank or poverty and humbleness — and none of it may be argued all one way.

斗數至玄至微，理旨難明，雖設問於百篇之中，猶有言而未盡，至如星之分野，各有所屬，壽夭賢愚，富貴貧賤，不可一概論議。

The book is full of judgements like this. This site applies them to a chart a line at a time, each quoted and its section named. What it declines — the clauses that fix a woman’s fate by her sex, the readings of children’s charts, the medical ones — is listed on the method page, each with its reason. The method

It and BaZi

BaZi reads the four pillars of the birth moment and their elements; Purple Star reads which stars land in which palace. Two readings of one moment, and both need the right birth hour: half an hour out, and both charts change. One birth, read both ways · Why half an hour matters