M02 · LESSONS 13–19

Module 2 · Astronomy and the Chinese Calendar (Lessons 13–19)

Ancient Chinese sky maps served several purposes: locating celestial regions, recording the positions of the sun, moon, and planets, organizing ritual and political time, and interpreting omens. This module distinguishes those uses. The Three Enclosures and Twenty-Eight Mansions are star-region systems; the Four Symbols group those mansions by direction; the Seven Luminaries are the sun, moon, and five visible planets. The Dipper, solar terms, lunar months, timekeeping, and historical omen-reading each belong to related but distinct frameworks.

Lesson 13 · Mapping the Sky: Three Enclosures, Four Symbols, and Twenty-Eight Mansions#

Learning goals#

Describe how traditional Chinese sky regions were organized.
Name the Four Symbols and the Twenty-Eight Mansions.
Explain what the Seven Luminaries are.

Lesson#

Ancient observers divided and named the sky to identify regions, track the sun, moon, and planets, and fit celestial observations into ritual and political order. A xingguan (asterism) is a named group of stars. The Three Enclosures are large asterism regions near the north celestial pole. The Twenty-Eight Mansions divide the region through which the moon appears to move into twenty-eight unequal sections. They are not the same as the boundaries of the International Astronomical Union’s modern eighty-eight constellations.

The Four Symbols group the Twenty-Eight Mansions into four directional sets of seven, each associated with a mythic creature. The Seven Luminaries are a separate category: the sun, moon, and five planets visible to the naked eye.

Symbol	Direction	Season	Seven Mansions
Azure Dragon	East	Spring	Jiao, Kang, Di, Fang, Xin, Wei, Ji
Black Tortoise	North	Winter	Dou, Niu, Nü, Xu, Wei, Shi, Bi
White Tiger	West	Autumn	Kui, Lou, Wei, Mao, Bi, Zui, Shen
Vermilion Bird	South	Summer	Jing, Gui, Liu, Xing, Zhang, Yi, Zhen

The Three Enclosures are the Purple Forbidden Enclosure (around the north celestial pole, symbolically the emperor’s court), the Supreme Palace Enclosure (government), and the Heavenly Market Enclosure (marketplace). The name Zi Wei Dou Shu, a traditional star-based destiny-calculation system, comes from the Purple Forbidden Enclosure.

The five planets had traditional names: Jupiter was Suixing (Year Star), Mars Yinghuo (Wavering Fire), Saturn Zhenxing or Tianxing (Quelling/Filling Star), Venus Taibai (Great White), and Mercury Chenxing (Chronicle Star). Together with the sun and moon, these make the Seven Luminaries. In feng shui, “Azure Dragon on the left, White Tiger on the right, Vermilion Bird in front, Black Tortoise behind” transfers the Four Symbols to a ground plan; that application appears in Module 8.

The lacquered box lid from the tomb of Marquis Yi of Zeng, excavated in Suixian, Hubei, in 1978, bears the names of the Twenty-Eight Mansions and images of a dragon and tiger. The tomb dates to about 433 BCE. The artifact is evidence that these mansion names and images existed by that period. It does not by itself establish when the entire system first formed or prove that the design is a precise observing log. To read the artifact, first establish its date and archaeological context, then identify the labels and images, and only then discuss the cosmology or ritual order it may express. The Hubei Provincial Museum notes that scholars have used it to propose an observation date; that is a modern reconstruction, not a date written on the object.

The Records of the Grand Historian, “Treatise on the Celestial Offices,” is an early systematic Chinese account of astronomy. When reading it, keep the different levels apart: the Three Enclosures divide the northern sky, the Four Symbols group the Twenty-Eight Mansions, and the Seven Luminaries name moving celestial bodies. The mansions are not twenty-eight equal modern constellations. In Wang Bo’s “Preface to the Pavilion of Prince Teng,” “the stars divide into Yi and Zhen” uses an old correspondence between Hongzhou and those mansions; it is not a precise modern star coordinate for Nanchang.

Practice#

Write the Twenty-Eight Mansions from memory, grouped by the Four Symbols.
On a clear night, locate the Big Dipper. In winter, find the three stars of Orion’s belt, traditionally associated with the Shen Mansion.
Explain why “Shen and Shang” became a metaphor for people who never meet: Shen is in the west and Shang (the Xin Mansion) in the east, appearing at different times.

Check your understanding#

What are the Three Enclosures?
Which Symbol includes the Mao Mansion?
Which planet was called Yinghuo?

Answers: 1. Purple Forbidden, Supreme Palace, and Heavenly Market. 2. The White Tiger of the west. 3. Mars.

Lesson 14 · The Dipper, Month-Branches, Jupiter, and Grand Treasurer#

Learning goals#

Explain the traditional ideas of month-branch and “establishing Yin.”
Distinguish Jupiter from the calendrical Grand Treasurer.
Understand the traditional Three Calendar Beginnings.

Lesson#

The Dipper’s handle was used as a seasonal pointer. Doujian (“Dipper construction”) relates the direction of the handle at a specified time to seasonal directions and the twelve earthly-branch sectors. A yuejian is the branch assigned to a month; Jianyin (“establishing Yin”) means treating the Yin month as the first month of the year. These are traditional descriptions based on observation. The handle does not point to one fixed direction on every night: the hour, location, horizon, and season matter.

The “Three Beginnings” describe three historical choices for the year’s first month: the Xia calendar began with the Yin month, the Shang with Chou, and the Zhou with Zi. The lunar calendar used today follows the Xia beginning.

Jupiter is Suixing, the Year Star. Ancient chronologies used its position among the Twelve Stations to mark years. Because Jupiter’s orbital period is about 11.86 years, treating it as an exact twelve-year cycle accumulates error. Traditional calendrical models also used Taisui (Grand Treasurer), also called Suiyin or Taiyin, as a calculated marker moving through the twelve branch sectors in the opposite direction. In this context Taisui is a calendrical symbol, not a real planet traveling backward. Later, Taisui was personified as the deity of the year; that belongs to a different history of belief.

The Heguanzi, “Circulation,” says: “When the Dipper’s handle points east, all under heaven is spring; south, summer; west, autumn; north, winter.” The received text’s date and authorship have been debated. This passage expresses the traditional idea of reading the month from the handle’s direction at dusk: Yin for the first month, Mao for the second, and so on.

After the Eastern Han, sexagenary year names continued to be used. The development of the system should not be reduced to the claim that Taisui was the single source of earthly-branch year numbering. Later popular belief personified Taisui as a yearly deity and developed the expression “offending Taisui,” discussed with almanac customs in Module 4.

Practice#

Draw the twelve earthly branches around a circle with Zi at the bottom (north), then mark the traditional seasonal directions of the Dipper’s handle.
Explain why the first lunar month is called the Yin month in the Xia calendar convention.
In one sentence, explain the calendrical role of Taisui.

Check your understanding#

In the traditional saying, what season is associated with the handle pointing north?
Which month did the Xia, Shang, and Zhou calendar beginnings use?
How are Taisui and Jupiter related in traditional calendrical models?

Answers: 1. Winter. 2. Yin, Chou, and Zi, respectively. 3. Taisui is a calculated marker placed opposite Jupiter’s direction through the twelve sectors; it is not an actual retrograde planet.

Lesson 15 · The Sun and the Twenty-Four Solar Terms#

Learning goals#

Explain how solar terms are defined.
Distinguish a “solar node” (jie) from a “midpoint” (zhongqi).
Learn how to verify an exact solar-term time and time zone.

Lesson#

The Twenty-Four Solar Terms mark the sun’s position through the year. A guibiao is a gnomon and horizontal base used to measure the noon shadow; ancient observers tracked seasonal change through the shadow’s length. The modern astronomical definition sets a term at each 15-degree step in the sun’s apparent ecliptic longitude. The winter solstice is at 270 degrees and the Beginning of Spring at 315 degrees. These are exact astronomical moments, so they do not occur at the same clock time each year.

In the stem-branch calendar, a month is commonly divided into one jie (solar node, marking a month-boundary) and one zhongqi (midpoint). The older pingqi method divided the year into twenty-four equal time intervals; the dingqi method uses the sun’s actual position. The Qing Shixian Calendar adopted the latter in 1645. Because tables may use different time zones, convert them before comparing. For example, Japan’s National Astronomical Observatory publishes in UTC+9, one hour ahead of Beijing time (UTC+8).

Season	Solar nodes (jie, month boundaries)	Midpoints (zhongqi)
Spring	Beginning of Spring, Awakening of Insects, Pure Brightness	Rain Water, Spring Equinox, Grain Rain
Summer	Beginning of Summer, Grain in Ear, Minor Heat	Grain Full, Summer Solstice, Major Heat
Autumn	Beginning of Autumn, White Dew, Cold Dew	End of Heat, Autumn Equinox, Frost Descent
Winter	Beginning of Winter, Major Snow, Minor Cold	Minor Snow, Winter Solstice, Major Cold

A common mnemonic in Chinese is: “Spring rain, insects awaken; spring clears, grain rains; summer fills, grain ears, heat follows; autumn begins, dew appears, cold and frost descend; winter snow, winter begins, minor and major cold.” The exact English names vary across translations.

The term times below are examples from the Hong Kong Observatory’s 2026 almanac, in Beijing time. They illustrate how month boundaries work; dates and times must be checked for each year.

Term	Example time	Month-branch change
Beginning of Winter	2026-11-07 17:52	Enters Hai month
Minor Snow	2026-11-22 15:23	—
Major Snow	2026-12-07 10:53	Enters Zi month
Winter Solstice	2026-12-22 04:50	—
Minor Cold	2027-01-05 22:10	Enters Chou month
Major Cold	2027-01-20 15:30	—
Beginning of Spring	2027-02-04 09:46	Enters Yin month; stem-branch year changes to Dingwei

In 2016, UNESCO added the Twenty-Four Solar Terms to its Representative List of the Intangible Cultural Heritage of Humanity.

For a boundary example, the Observatory lists the Beginning of Winter in 2026 at 17:52 on November 7. A time of 17:40 is before the boundary and 18:00 after it. If a table instead lists 18:52, check whether it uses UTC+9 before assuming the calculation conflicts. This only identifies a time boundary; applying it to stem-branch months also requires stating the calendar convention.

Practice#

List the twenty-four terms and mark the twelve month-boundary solar nodes.
Name the month branch that begins at each node, from Yin at the Beginning of Spring through Chou at Minor Cold.
Check a current almanac and identify the two solar terms between which today falls.

Check your understanding#

What is the sun’s ecliptic longitude at the winter solstice?
How does dingqi differ from pingqi?
Which month branch begins after Major Snow?

Answers: 1. 270 degrees. 2. Dingqi uses the sun’s actual position at each 15-degree step; pingqi divides the year into equal time intervals. 3. Zi.

Lesson 16 · The Moon and the Chinese Lunisolar Calendar#

Learning goals#

Explain why the Chinese calendar is lunisolar.
Describe the principle used to insert leap months.
Know how to verify a lunar-calendar date.

Lesson#

The Chinese calendar is lunisolar: months follow the moon’s phases, while leap months keep the year aligned with the seasons. A shuo (new moon) is the moment when the sun and moon have the same apparent ecliptic longitude; a wang (full moon) is when their longitudes differ by 180 degrees. The interval from one new moon to the next is a synodic month, about 29.53 days. A lunar month therefore has 29 or 30 days, and the civil date containing the new moon in Beijing time is designated the first day of the month.

Twelve synodic months are about eleven days shorter than a solar year. Leap months correct this difference. “Seven leap months in nineteen years” is a useful approximation, not a mechanical rule for placing every leap month. Under the current calendrical standard, the month containing the winter solstice is the eleventh month. If there are thirteen lunar months between one winter solstice and the next, a leap month is inserted; the first month in that interval without a zhongqi (midpoint solar term) is selected. Midpoints include the winter solstice, Rain Water, and the spring equinox. To identify a leap month, check the full month sequence for that year.

The national standard GB/T 33661—2017 specifies the calculation and publication of the Chinese calendar, using Beijing time and the 120° east standard meridian. For example, the Observatory lists the new moon on November 9, 2026, at 15:02 Beijing time. Since that civil day contains the new moon, the day is the first day of the tenth lunar month; the fact that the new moon occurs in the afternoon does not make the date the second day.

Example dates from the Hong Kong Observatory’s 2026 almanac include November 9, 2026, as the first day of the tenth lunar month; January 7, 2027, as the thirtieth day of the eleventh lunar month; and February 6, 2027, as Lunar New Year’s Day. Month names recur, but their Gregorian date ranges change from year to year.

Practice#

Use a calendar to find your lunar birthday this year and next year.
Compare nineteen solar years with 235 synodic months. How close are the totals?
Explain why Lunar New Year falls between late January and mid-February rather than on one fixed Gregorian date.

Check your understanding#

About how long is a synodic month?
What kind of lunar month is selected as a leap month under the current rule?
Why is the Chinese calendar called lunisolar?

Answers: 1. About 29.53 days. 2. The first month without a midpoint solar term in the relevant interval. 3. Months follow the moon, while the year and leap-month system keep them aligned with the sun and seasons.

Lesson 17 · Three Calendars, Double Hours, and True Solar Time#

Learning goals#

Distinguish the Gregorian, lunar, and stem-branch calendars.
Convert clock time to the traditional double hours.
Describe true solar time and the late-Zi-hour boundary issue.

Lesson#

The Gregorian calendar, Chinese lunar calendar, and stem-branch calendar use different boundaries. The Gregorian year begins on January 1 and its months follow fixed civil dates. The Chinese lunar calendar changes months at the new moon and inserts leap months. The stem-branch calendar divides months by solar terms, generally begins its year at the Beginning of Spring, and changes months at the twelve jie. A lunar eleventh month and a stem-branch Zi month are often close, but their boundaries do not always coincide.

Calendar	Year boundary	Month boundary
Gregorian	January 1	Fixed civil dates
Chinese lunar	Lunar New Year	New moon / first day
Stem-branch calendar	Beginning of Spring	Twelve solar nodes (jie)

Different traditional systems may use different inputs. BaZi year and month pillars and seasonal strength generally use the stem-branch calendar; time-based Meihua Yishu and some Xiao Liuren methods use lunar month and day; Zi Wei Dou Shu generally uses the lunar calendar; almanac rules combine the day’s stem-branch with the stem-branch month. Always name the convention before calculating.

Traditional double hours divide the day into twelve periods of about two hours each. Zi hour crosses midnight, from 23:00 to 01:00.

Branch hour	Clock time	Branch hour	Clock time
Zi	23:00–01:00	Wu	11:00–13:00
Chou	01:00–03:00	Wei	13:00–15:00
Yin	03:00–05:00	Shen	15:00–17:00
Mao	05:00–07:00	You	17:00–19:00
Chen	07:00–09:00	Xu	19:00–21:00
Si	09:00–11:00	Hai	21:00–23:00

The “true solar time” used in some chart calculations adjusts standard clock time to local apparent solar time. Longitude correction converts from the 120° east standard meridian to the birthplace’s longitude; the equation of time is a separate seasonal correction because apparent solar motion is not uniform. Guangzhou, at about 113.3° east, is roughly 27 minutes behind Beijing’s standard meridian before the equation-of-time adjustment. Urumqi, around 87.6° east, differs by roughly two hours before that adjustment. These are approximations; state the inputs and method.

Birth times near Zi hour also require a stated day-boundary convention. Some systems treat 23:00–midnight as “late Zi” of the current day; others assign the entire Zi period to the next day or distinguish early and late Zi. Software defaults are not universal rules. Keep one convention consistent and report it.

Practice#

Write the twelve double hours from memory and convert eight clock times.
If someone is born on January 20, which stem-branch year is used before that year’s Beginning of Spring? Explain.
Estimate the longitude correction for your birthplace and record whether you included the equation of time.

Check your understanding#

Which calendar’s month is used in time-based Meihua Yishu?
What double hour contains 20:30?
Is local solar time in Chengdu (about 104° east) earlier or later than Beijing time, and by roughly how much before the equation-of-time correction?

Answers: 1. The lunar calendar. 2. Xu hour. 3. Earlier by about (120 − 104) × 4 = 64 minutes.

Lesson 18 · Astral Omen Reading and Terrestrial Correspondences#

Learning goals#

Understand that omen reading was one part of ancient astronomy.
Explain the theory of celestial-terrestrial correspondences (fenye).
Identify the Seven Luminaries and Four Excesses in later star-calculation traditions.

Lesson#

Ancient astronomy included observation for timekeeping, calendar calculation, ritual, and omen reading. Zhanhou (omen reading) interpreted celestial changes as signs concerning politics, war, or harvests. This practice was related to observation and calendrical work, but its interpretations are not modern astronomical causal conclusions.

The theory of fenye (“allocated fields”) paired celestial regions with terrestrial states or territories. Wang Bo’s phrase “the stars divide into Yi and Zhen” associates Hongzhou with the Yi and Zhen Mansions. Different texts can give different correspondences. This is a historical symbolic geography, not a set of modern map coordinates.

When reading a report of “Yinghuo guarding Xin,” first identify Yinghuo as Mars and Xin as the Heart Mansion. “Guarding” is a traditional term for a planet appearing to slow and remain near a mansion. Then separate the recorded observation, the omen attached to it, and later events narrated alongside it. A history placing two events together shows how the text connects them; it does not by itself prove that a documented prediction was made and confirmed in advance.

In later star-calculation systems, the Seven Luminaries are the sun, moon, and five planets. The “Four Excesses” (siyu) are Luohou, Jidu, Yuebo, and Ziqi, calculated positions in traditional systems rather than four additional naked-eye planets. Interpretations and calculation methods vary among texts. The system’s formation and the movement of astronomical knowledge should be studied through particular manuals and calculation materials, not reduced to one uncontested account of transmission.

The Book of Han, “Treatise on Astronomy,” records “Mars guarding the Heart Mansion” in the spring of 195 BCE and the emperor’s death in the fourth month. This can be studied as an example of how Han historians linked celestial events and political life. The passage alone does not provide a complete record proving that the death had been predicted in advance; correspondence with modern ephemerides must also be checked case by case.

The surviving omen literature gives substantial attention to states, rulers, war, and harvests, while personal destiny systems also developed in other traditions. Rather than generalizing that Chinese astrology was only about states and Western astrology only about individuals, compare the subject, calculation, and setting of particular texts.

Practice#

Look up the traditional fenye correspondence for your region and note which source you used.
Compare one Chinese omen text and one modern horoscope: identify three differences in subject or method without treating either as representative of every tradition.
Read the opening of the Records of the Grand Historian, “Treatise on the Celestial Offices.” What is the Dipper compared to?

Check your understanding#

Which city is associated with the phrase “the stars divide into Yi and Zhen”?
In “Mars guarding the Heart Mansion,” what are Yinghuo and Xin?
What are the Four Excesses?

Answers: 1. Hongzhou, present-day Nanchang. 2. Mars and the Heart Mansion, respectively. 3. Luohou, Jidu, Yuebo, and Ziqi.

Lesson 19 · Module Review and Assessment: Astronomy and Calendars#

Review method#

This assessment combines three types of task: naming mansion groups, explaining calendar rules, and converting times. Sort each error before correcting it. Confusing a lunar eleventh month with a Zi month means two calendar boundaries were merged; treating the Beginning of Winter as the same Gregorian date every year confuses an astronomical moment with a date label; omitting leap months means the lunar and solar cycles have not been related correctly.

Use one example from the Hong Kong Observatory’s 2026 almanac: the Beginning of Winter occurs at 17:52 on November 7, while the new moon occurs at 15:02 on November 9. The first is a stem-branch month boundary; the second identifies the first day of the tenth lunar month. They are two nearby but separate timelines. Record for each problem: inputs, rule, intermediate steps, answer, and source. For historical claims, also note the text’s date and distinguish it from later interpretations.

Closed-book assessment#

Suggested time: 40 minutes. Passing score: 80 out of 100.

Name the Three Enclosures. (6 points)
Write the Twenty-Eight Mansions, grouped by the Four Symbols. (20 points)
Give the traditional names of the five planets. (10 points)
Where does “When the Dipper’s handle points east, all under heaven is spring” appear? How is the month-branch derived? (8 points)
Explain the calendrical origin of Taisui. (8 points)
List the twelve month-boundary solar nodes and their branch months. (12 points)
State the leap-month rule and explain the approximation “seven leap months in nineteen years.” (10 points)
Which calendar is generally used for BaZi, Meihua Yishu, Zi Wei Dou Shu, and almanac month rules? (8 points)
What double hours include 22:10 and 06:50? (6 points)
Define fenye and give an example. (6 points)
Compare the common subject matter of some state-focused Chinese omen texts and modern individual natal astrology, while stating the limits of the comparison. (6 points)

Answer key for supplied items: 3. Suixing (Jupiter), Yinghuo (Mars), Zhenxing (Saturn), Taibai (Venus), and Chenxing (Mercury). 6. Beginning of Spring–Yin; Awakening of Insects–Mao; Pure Brightness–Chen; Beginning of Summer–Si; Grain in Ear–Wu; Minor Heat–Wei; Beginning of Autumn–Shen; White Dew–You; Cold Dew–Xu; Beginning of Winter–Hai; Major Snow–Zi; Minor Cold–Chou. 8. Stem-branch calendar; lunar calendar; lunar calendar; day stem-branch plus stem-branch month. 9. Hai hour and Mao hour. 11. As an introductory comparison, some Chinese official celestial treatises emphasize rulers, war, and harvests, while many modern Western horoscopes center individual natal charts; neither description covers every text or practice.

Module outcome#

You are ready to continue when you can distinguish the major sky-region systems, explain how lunar and solar boundaries differ, convert a time with stated assumptions, and read an omen text as historical evidence without treating its interpretation as a verified prediction.

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