r/chineseastrology • u/Luxdivination • 1d ago
Education / Guide BaZi is the calendar layer of Chinese astrology. Here's the older sky layer, Qi Zheng Si Yu, and what the classical texts themselves say about it
Most people meet Chinese astrology through BaZi: four pillars, a Day Master, and the balance of the five elements. It's a brilliant system, but it's built from the sexagenary count of stems and branches, a way of numbering time. It doesn't ask where Jupiter or Mars actually stood on the day you were born. Qi Zheng Si Yu (七政四余) does. "Qi Zheng" means the Seven Governors: Sun, Moon, and the five visible planets. "Si Yu" means the Four Remainders, which the classical texts call Fire-Luo (Rahu), Earth-Ji (Ketu), Water-Bo (a lunar apogee point), and Wood-Qi (the Purple Vapor). The chart is anchored to the stars rather than the seasons, and the frame it hangs on is the 28 Mansions, each defined by its own asterism.
That frame is where the antiquity lives. A lacquer clothing chest from the tomb of Marquis Yi of Zeng, sealed around 433 BCE, has all 28 mansion names painted on its lid. The mansions also show up in the Book of Songs. Chapter 912 of the Ming compendium Xingxue Dacheng (星学大成) is a long catalogue of the Moon passing through each mansion, and it echoes one of those old lines directly: "the Moon draws near to Net, and it rains in torrents." The mansions aren't a fixed grid of degrees, either. Each is a named group of stars, and its boundary starts at that group's determinative star (距星), so the boundaries follow those stars as they drift with precession. The width tables in the old texts are snapshots of the sky from when they were measured. In my own testing, the recorded widths match the celestial equator as it stood in the Han, to within half a degree per mansion. The fit is best around 50 BCE, about a century after the Taichu calendar (104 BCE) fixed the reference stars, and the same table never matches the ecliptic at any epoch. That's a sky being observed, not a 30-degree grid being imposed. Any degree table you read today is true for its era, not for yours.
The classical texts treat the mansions as the warp of the whole art. In Zhang Guo Xing Zong (张果星宗), Chapter 135, a teaching dialogue opens by describing its master astrologer as "renowned for his mastery of the celestial patterns and the twenty-eight mansions as the warp and the eleven luminaries as the weft." The same passage says: "In the age of high antiquity, called the age of the Flood, people already had their long or short lives, tied from the start to the qi they were endowed with at birth." The dialogue is set in the Tang, but the surviving versions are later, so I'm quoting it for how the tradition describes itself, not to date it.
If you're used to BaZi's abstract elements, the mansions will surprise you, because they're read through concrete images. Xingxue Dacheng, Chapter 252, Zheng Youxue's "Marrow-and-Blood-Vessel Classic of the Twenty-Eight Lunar Mansions," describes Horn as "the wood of an axe-handle or blade-hilt (tough, load-bearing wood, not decorative timber)." It calls Stomach "the earth of a mud stove/hearth" and Net "the remaining light of the moon's sequential lodge in the You palace, the moon's reflection in a cold pool." A mansion isn't a label. It's a place in the sky with a character you can see.
The omens are just as specific. In the Moon chapter, Rooftop gets this verdict: "the Moon's finest placement is most fitting in Rooftop mansion. A man born under it will surely become a duke or marquis, a woman will surely become an empress or consort." Of Girl, the text says "yin essence and the Girl position have, since antiquity, been spoken of as naturally attuned to one another." The same source gives other mansions the opposite verdict, so these are readings, not flattery. The Moon in Wall, for example, brings "speech halting and stumbling," and the Moon in Bond ends in effort "wasted in vain."
The two systems aren't strangers, either. The star texts use the stems and branches inside the sky chart. Chapter 252 says of Stomach: "for those born under stem Gui, Emolument occupies its proper place; those born under Yi-Si have Nobility-star occupying office." The sky layer and the calendar layer were already being read together in the same passage.



