Zi Wei Dou Shu (紫微斗數, Zǐwēi Dǒushù), usually rendered in English as Purple Star Astrology, is one of the two systems of Chinese natal astrology that are still practised widely, the other being BaZi, the Four Pillars of Destiny. Both take the same raw material — the date and hour of a birth — and both work from the same foundations of Yin and Yang, the Five Elements and the Heavenly Stems and Earthly Branches. What they do with that material is what separates them.

What the name means

The system is named after its first and most important star, 紫微 Zǐwēi, which in Chinese astronomy denotes the region around the north celestial pole — the Purple Forbidden Enclosure (紫微垣), the imperial centre of the heavens. 斗數 Dǒushù means "star calculation" or "star enumeration", and it names the method honestly: this is a system that places named stars onto a grid and reads what they say. The Ziwei star stands at the head of the chart the way the pole stands at the head of the sky, and the positions of the stars around it follow from where it lands.

The chart at a glance

A Purple Star chart is a square of twelve palaces built on the twelve Earthly Branches. One of those palaces is the Life palace (命宮, mìnggōng), and the other eleven take their places around it in a fixed sequence: Siblings, Spouse, Children, Wealth, Health, Travel, Friends, Career, Property, Fortune and Parents. Every domain of a life therefore has a seat of its own, and the reading is largely a matter of seeing which stars sit in which seat — the twelve palaces are the frame of the whole system.

Into that frame go the fourteen major stars, the two groups led by Ziwei and by Tianfu, along with a much larger set of supporting and minor stars. Over them run the Four Transformations — Wealth, Power, Fame and Obstruction — which are assigned by the Heavenly Stem of the birth year and are treated as the most decisive layer of the reading. And because a chart describes a life rather than a single moment, its twelve palaces also become the ten-year limits and annual periods through which a practitioner follows the timing of events.

How it differs from BaZi

BaZi reads eight characters — four stems and four branches — and describes a life through the balance and interaction of the Five Elements and the Ten Gods. Purple Star Astrology reads named stars in dedicated palaces. The contrast is usually stated like this:

	Zi Wei Dou Shu	BaZi (Four Pillars)
Structure	Twelve-palace chart of stars	Four stem-branch pairs
Unit of reading	Named stars, each with its own character	Elemental relations and the Ten Gods
Life domains	Each mapped to its own palace	Inferred from the pillars
Strength	Concrete, situational description	Structural and cyclical analysis

The two are not rivals and are often read together. Where BaZi answers "what is this chart made of", Purple Star Astrology tends to answer "where in a life does it show".

The schools

As with the feng shui schools, more than one tradition of interpretation has grown up around the same chart. The Three-Conjunction school (三合派, Sānhé pài) reads the stars that share a palace and the relationships between palaces, and is the older, more descriptive approach. The Flying Star school (飛星派, Fēixīng pài), associated with modern Taiwanese practice, concentrates on the Four Transformations and the way they travel from palace to palace and year to year. Most contemporary practice draws on both, and where they disagree the chart is read against the school named.

How to use this section

The articles below follow the order in which a chart is actually read. Building the Chart sets out how the twelve palaces and the stars are placed from a birth date; the twelve palaces and the fourteen major stars are the vocabulary; the Four Transformations are the layer that gives the chart its sharpest statements; and limits and timing shows how the fixed chart is read across a life. To cast a chart from your own data rather than by hand, the Zi Wei Dou Shu calculator does the placement.