The Twenty-Eight Lunar Mansions: Celestial Coordinate System

The Twenty-Eight Lunar Mansions, or 二十八宿, are twenty-eight divisions of the sky established in early Chinese astronomy along the celestial equator. They were used to mark the positions of the sun, moon, and five visible planets. In traditional almanacs, the mansions also serve as a daily cycle, with one mansion assigned to each day in a fixed rotation. This article describes how the system is structured, how the daily rotation works, how the mansions were treated in old calendrical custom, and how the system relates to other almanac cycles. It does not provide day-selection advice.

二十八宿的由来与四象分组

The twenty-eight mansions are twenty-eight zones traced along the celestial equator by ancient astronomers. They form a coordinate-like framework for recording the apparent movements of the sun, moon, and planets. Rather than being a single continuous band, the mansions are grouped into four sets of seven, each set associated with one of the four emblematic animals known collectively as the Four Symbols, or 四象.

The seven mansions of the eastern group belong to the Azure Dragon, or 青龙. The seven of the northern group belong to the Black Tortoise, or 玄武. The seven of the western group belong to the White Tiger, or 白虎. The seven of the southern group belong to the Vermilion Bird, or 朱雀. This grouping is a formal division of the sky, not a daily cycle. It gives each mansion a fixed regional identity within the larger framework of the heavens. In almanac texts, the same groupings are printed as part of the standard notation for each day, but the grouping itself derives from the astronomical division of the sky.

二十八宿值日是怎么轮的

In the almanac, the twenty-eight mansions rotate day by day. One mansion is assigned to each day, and the cycle repeats every twenty-eight days. The rule of rotation is fixed. Given a date, the mansion governing that day can be calculated directly. There is no variation by person, place, or circumstance. The sequence is the same for everyone, and it proceeds continuously without interruption.

Because the cycle is twenty-eight days long, it forms a fixed correspondence with the seven-day planetary week. Twenty-eight is exactly divisible by seven, so the same weekday always falls on the same mansion within the cycle. This is why, in older almanacs, the mansion name is often printed beside a weekday name. The side-by-side arrangement is not an independent judgment about the day; it is a mechanical result of the two cycles sharing a common period. The mansion changes in the same order, and the weekday repeats in the same order, producing a stable pairing.

The rotation of the mansions is therefore a calendrical sequence rather than an astronomical observation of the moment. It is predictable from the calendar alone. In this respect it differs from the original astronomical function of the mansions, which involved marking observed celestial positions. The daily almanac usage is a fixed layer applied over the calendar.

各宿在旧例中的宜忌说法

In older almanac practice, each mansion was also paired with an animal. For example, the Horn mansion, or 角宿, was paired with a flood dragon, or 蛟. These pairings come from the traditional conventions of almanac literature. They are not derived from the astronomical positions of the stars. They belong to the layer of symbolic association that accumulated around the mansions over time.

Each mansion, in this old usage, carried its own set of statements about what was considered suitable or unsuitable. These statements appear in historical almanacs as customary notes attached to the mansion of the day. They are sometimes expressed as things to be preferred or avoided, such as beginning a journey, opening a building, or conducting a ceremony. The specific lists vary by source and period. What is constant is that they are old conventions. They are not presented here as rules to be followed, and this site does not evaluate their validity.

The animal pairings and the associated customs are part of the same traditional layer. They gave each mansion a distinct character in the popular almanac, but they should not be confused with the astronomical structure from which the mansions originated. In the reference material used by this site, the animal pairing is recorded as a historical convention, not as a claim about the natural world.

二十八宿与建除、值神并行

The rotation of the twenty-eight mansions is independent of two other common almanac systems: the twelve Jianchu deities, or 建除十二神, and the daily value deities, or 值日星神. Each of these systems operates by its own cycle. The mansion of the day, the Jianchu deity of the day, and the value deity of the day are printed together on the same almanac page, but they do not determine one another.

The Jianchu system has its own sequence of twelve terms. The value deity system has its own list of daily deities. The mansion system has its own twenty-eight-day sequence. A day may be governed by a particular mansion, a particular Jianchu term, and a particular value deity at the same time, but these assignments are parallel. They do not combine into a single judgment. The presence of one does not override or confirm the other. In the structure used by this site, the three systems are treated as separate layers of the traditional almanac.

This means that the mansion of the day cannot be used to infer the Jianchu term, nor the reverse. The value deity of the day likewise stands apart. Each cycle is calculated from its own rules. The same date may carry any combination of the three, depending on where each cycle falls. The almanac presents them side by side as parallel notations.

本站不据此裁定日子

The result of the mansion cycle depends only on the date. The same day gives the same mansion to every person. The cycle does not take into account an individual’s birth data, name, gender, or any personal factor. It is a public time order: one mansion for one day, shared by all. In this respect it is like the weekday or the date itself. It does not describe a personal condition.

This site’s engine can calculate the sexagenary characters for any date. That includes the day pillar and other cyclic markers used in traditional calendrical work. However, the site does not publish day-selection advice. It does not judge a day as auspicious or inauspicious based on the mansion. It does not use the mansion to recommend or discourage action. The mansion is reported as part of the calendar record, not as a ruling.

What does vary by person is the relationship between the day’s sexagenary characters and the person’s own Four Pillars. That relationship depends on the complete birth data: year, month, day, and hour. Without the full set, no personal comparison can be made. The mansion cycle, by contrast, is not personal. It remains a fixed, shared sequence. The site’s role is to show where the cycle falls, not to draw conclusions from it.