To Understand Why Zi Wei Dou Shu Is Accurate
First you have to understand what Zi Wei Dou Shu (紫微斗數) is built around.
It is built around the Moon.
Zi Wei Dou Shu reads the inertia of desire, the part that does not change
The Moon is Tai Yin (太陰). It is Tai Yin damp earth, which is Ji earth (己土).
In Chinese, the characters for liver, spleen, lungs, kidneys, stomach, gallbladder and intestines (肝脾肺腎胃膽腸) are all written with the flesh radical, which has the same form as the character for moon (月).
So the Moon is the body, and it is yin. Yin is the hidden, unseen side.
It stands for what does not change, and for desire.
So what Zi Wei Dou Shu reads is this unchanging inertia of desire.
You can see it in the star-placement rules
Then why is Zi Wei Dou Shu centered on Tai Yin, the Moon?
You can see it in the star-placement rules (安星訣, An Xing Jue).
The first month starts at the Yin (寅) palace. Count forward to the birth month, then backward to the birth hour, and that is the Life Palace (命宮). The first month here is the lunar calendar, starting on lunar New Year’s Day.
It is not the day of Li Chun (立春), the solar term on which Tai Sui changes over.
Once the Life Palace is placed, the year stem is used to give the Life Palace its stem and branch.
Then that stem and branch gives the Na Yin (納音).
Na Yin is sound, the sound born when heaven and earth join.
The bureau number of that Na Yin is then divided into the lunar day of birth.
That day runs from the 1st to the 30th of the lunar month, so it too is tied to the Moon.
This is how the Zi Wei (紫微) star is placed.
So when I say Zi Wei Dou Shu is centered on Tai Yin, the Moon, this is where you can see it.
PS: Tai Yin here means the real Moon in the sky, not the Tai Yin star on a Zi Wei Dou Shu chart. The Tai Yin on the chart is placed from Tian Fu (天府).
To see which palace your own Life Palace falls in, you can cast a Zi Wei Dou Shu chart on the chart calculator.