The Twenty-Eight Lunar Mansions: Chinese Mapping of the Sky

The Chinese 28 lunar mansions

Chinese astronomers were some of the most skilled of the ancient world. Entire dynasties diligently mapped the night sky and kept careful records of their findings. Observation records date back to the Shang dynasty (1600 BCE to 1046 BCE), with refinement continuing for 3,000 years. Star name records date to 1200 BCE.

The Chinese astronomy system is based on observing the Moon’s monthly path against a background of stars. This system divides the sky into 28 segments. Each of the 28 segments is called a mansion or xiù (宿), and the Moon moves through them at the rate of roughly one per night.

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This is somewhat like the 27 segments of Indian astronomy, but differs in that the Chinese system has segments of varying sizes. Mansions range from a small segment of 2 degrees to more than 30 degrees across. Each mansion runs from one anchor star, called the determinative star, to the anchor star of the next, so the spacing between determinative stars sets each mansion’s width. Mansion boundaries are drawn as lines running from pole to pole through each determinative star, an equatorial-style construction tied to the sky’s daily rotation rather than to the ecliptic shape used by the Indian system.

While a few Chinese astronomers did argue that the Earth was a sphere, for the most part, the prevailing Chinese belief was that the sky was a sphere or hemisphere, and the Earth remained a stationary disc at the bottom, floating in water, with the Sun and celestial pole orbiting the Earth. It was not until Jesuit missionaries came to China in the 1580s CE that views began to change.

The role of astronomy in ancient China

Astronomy in China was closely tied to the dynasty in power. It was used for ritual, timekeeping, prediction, and planning. If something went wrong, the ruler held his astronomers responsible. Chinese timekeeping was also unusually complex, since it had to reconcile lunar and solar cycles that do not naturally align.

Heaven as an imperial court

Astronomy was political in China. Chinese astronomy is arranged around the idea that the heavens are a mirror of the imperial state. In the sky, individual stars were mapped to stand for officials, palaces, ceremonial spaces, military camps, and even a marketplace.

The three enclosures (三垣, sānyuán) divide the region around the celestial pole: the Purple Forbidden Enclosure is found in the center, directly around the pole, while the Supreme Palace Enclosure and the Heavenly Market Enclosure lie much further away from it. The 28 mansions form the outer ring circling these three enclosures.

Purple Forbidden Enclosure (紫微垣, Zǐwēi Yuán): the region around the celestial pole, the emperor’s own palace. The pole is the still point around which the sky turns, so placing the emperor there is deliberate: the whole sky revolves around him, as the state revolves around the throne. The Forbidden City echoes the name.
Supreme Palace Enclosure (太微垣, Tàiwēi Yuán): the seat of government, the court of administration, ministers, and officials.
Heavenly Market Enclosure (天市垣, Tiānshì Yuán): the celestial marketplace, the realm of commoners and trade.

The court astronomers’ job was to read the sky as a stream of messages about how well the emperor governed: comets, eclipses, and guest stars (sudden new stars, now called novae and supernovae) were taken as verdicts on the emperor’s conduct.

The four symbols

The 28 mansions are grouped into four sets of seven, each tied to a cardinal direction, a season, a color, and one of the Five Phases (the Chinese elements). The mansions are anchored to small star patterns.

The Azure Dragon symbolizes the east and spring; its phase is Wood. The Vermilion Bird represents the south and summer; its phase is Fire. The White Tiger symbolizes the west and autumn; its phase is Metal. The Black Tortoise represents the north and winter; its phase is Water. Earth, the fifth phase, takes the center or pole rather than a direction.

These four creatures and the pole organize the whole sky into quarters and a center, and the colors that name them, azure, vermilion, white, and black, carry over into how the tradition’s charts are drawn.

The twenty-eight mansions

Listed in order from the first mansion, with the determinative star that anchors each. Where a mansion contains a famous star that is not the formal anchor, that is noted.

Azure Dragon of the East (mansions 1 to 7), spring, Wood

1. 角 Jiǎo (Horn), α Virginis (Spica)

2. 亢 Kàng (Neck), κ Virginis

3. 氐 Dī (Root), α Librae

4. 房 Fáng (Room), π Scorpii

5. 心 Xīn (Heart), σ Scorpii (mansion contains Antares)

Black and white woodblock diagram of a circle divided into four quadrants by diagonal lines, ringed by twenty-eight small cartouches each holding a Chinese character naming a lunar mansion, with the four quadrant names written at the center and four larger characters at the corners of the page.

6. 尾 Wěi (Tail), μ Scorpii

7. 箕 Jī (Winnowing Basket), γ Sagittarii

Black Tortoise of the North (mansions 8 to 14), winter, Water

8. 斗 Dǒu (Dipper), φ Sagittarii

9. 牛 Niú (Ox), β Capricorni

10. 女 Nǚ (Girl), ε Aquarii

11. 虚 Xū (Emptiness), β Aquarii

12. 危 Wēi (Rooftop), α Aquarii

13. 室 Shì (Encampment), α Pegasi (Markab)

14. 壁 Bì (Wall), γ Pegasi (Algenib)

White Tiger of the West (mansions 15 to 21), autumn, Metal

15. 奎 Kuí (Legs), η Andromedae

16. 婁 Lóu (Bond), β Arietis (Sheratan)

17. 胃 Wèi (Stomach), 35 Arietis

18. 昴 Mǎo (Hairy Head), 17 Tauri (in the Pleiades)

19. 畢 Bì (Net), ε Tauri (Ain, with the Hyades)

20. 觜 Zī (Beak), φ1 Orionis (smallest mansion, ~2°)

21. 參 Shēn (Three Stars), ζ Orionis (Orion’s belt)

Vermilion Bird of the South (mansions 22 to 28), summer, Fire

22. 井 Jǐng (Well), μ Geminorum

23. 鬼 Guǐ (Ghost), θ Cancri (near the Beehive, M44)

24. 柳 Liǔ (Willow), δ Hydrae

25. 星 Xīng (Star), α Hydrae (Alphard)

26. 張 Zhāng (Extended Net), υ1 Hydrae

27. 翼 Yì (Wings), α Crateris

28. 軫 Zhěn (Chariot), γ Corvi

The longest observational record

Chinese records of the sky are the longest kept by any civilization. Court astronomers kept careful records of eclipses as far back as 722 BCE and recorded the Crab Nebula supernova of 1054 CE.

The earliest physical records that archaeologist have unearthed are oracle bones from the Shang dynasty (~1200 BCE). They uncovered turtle-shell and ox-scapula fragments used for divination, some of which were scratched with constellation names that later became mansion names.

The Canon of Yao (Yao Dian), part of the Book of Documents, names four stars that marked the seasons by their position in the evening sky; those four fall into mansions 5 (Heart 心, Antares), 11 (Emptiness 虛), 18 (Hairy Head 昴, the Pleiades), and 25 (Star 星, Alphard). The date is uncertain, but it drew on traditions already established by the time it was compiled.

The heavens-as-bureaucracy idea is set down in Sima Qian’s Shiji (Records of the Grand Historian, ~100 BCE) and the Suzhou star chart from 1247 CE is a surviving carved-stone star map depicting the complete mansion system with star positions.

Across these diverse dynasties, court astronomers kept observational records for more than 3,000 years.

Did China and India develop their systems independently?

The obvious question is whether the Chinese and Indian systems were independent or borrowed.

The parallels are easy to see: a similar count (27 for India, 28 for China), both built around the lunar month, both using small star patterns as markers.

But they have differences too; both are organized around different reference circles; China’s pole-to-pole, equatorial-style divisions versus India’s ecliptic-based segments. They use different boundary stars, and the cultural overlays diverge, since the Indian system has no equivalent to the celestial bureaucracy.

One theory is that the systems evolved separately at first, but that, with the advent of Buddhist influences between India and China from the 1st century CE onward, they influenced each other. Some also argue that ancient Babylonian ideas influenced Chinese astronomy.

Reading a Chinese-traditional star chart

A Chinese-traditional chart turns all of this into a single map. The four symbols are laid over the equatorial sky, the 28 mansions are marked out in order, and the major stars within each are identified.

What makes such a chart distinctive is that the stars carry their Chinese mansion names alongside their modern catalog designations, and in this system, a star’s name is often its address. Antares is also Xīn Sù Èr (心宿二), the second star of the Heart mansion; Aldebaran is also Bì Sù Wǔ (畢宿五), the fifth star of the Net mansion. Read that way, each label points back to the mansion it belongs to and the position it holds within it.