1. The 28 Lodgings: Where Does the Moon Stay Each Night?
Imagine a bright star near the moon one night. The next night, the moon has moved slightly away from that star. The moon continues to move among the stars, completing a full circle of the sky and returning to its starting position in about 27.32 days. This cycle is called the sidereal month [1]. Ancient Chinese people divided the sky along this path into 28 sections, calling each a "lodging." They viewed the moon as passing through roughly one section per day, so its location each night could be described by asking, "Which lodging is the moon staying in tonight?" [1]. These lodgings are also known as "star lodgings" or "star inns" [3].
However, because 28 and 27.32 are not the same number, the moon does not move exactly one section per day. Each section is defined by a reference star (called a distance star) and the next reference star, so the width of the sections varies [4].
2. The 28 Lodging Names on a Lacquer Box Lid from the Tomb of Marquis Yi of Zeng
A famous artifact listing all 28 lodging names is the lid of a lacquer box found in the tomb of Marquis Yi of Zeng in Hubei Province, China. The names are written in red characters, accompanied by paintings of the Azure Dragon and White Tiger. The date is estimated to be around 433 BC, based on the date inscribed on the box, rather than the year it was manufactured [7]. The prototype of the 28 lodgings is thought to have been established around the 8th to 6th centuries BC. However, scholars disagree on whether the origin was China or India, so it is safest to consider it as originating in China [2].
The 28 lodgings are assigned to the four cardinal directions, with seven in each direction. Each direction corresponds to one of the Four Symbols: Azure Dragon, Black Tortoise, White Tiger, and Vermilion Bird [2][5]. This divides the moon’s path into four segments of seven lodgings each. Outside the moon’s path, there were many other star groups with different naming conventions.
3. How Chinese Constellations Used Court Titles for Stars Around the North Star
Chinese constellations are called "star officials." The word "official" refers to a bureaucrat, and star groups were named after officials and government offices. Around the North Star, star officials are named after the Emperor, Crown Prince, Empress, and the Jade Throne, reflecting the structure of the imperial court in the sky [6]. These names were not limited to the court; they also came from weather, animals, official duties, tools, and palace rooms. The sky was seen as a world of the court and its workers [6].
The sky is divided into the northern "Three Enclosures" and the 28 lodgings around the equator [6]. While the West divides the sky into 88 constellations, China has about 283 star officials, and the designs are quite different. The figure of "about 283" is a rough estimate based on the Suzhou Star Chart from the Song Dynasty. The original chart was created by Huang Shang in 1193 and carved into stone by Wang Zhiyuan in 1247, showing 283 star officials and 1,565 stars. However, some sources count 280 star officials and 1,434 stars, so the exact number is not fixed [8].
4. The Chinese-Style Star Map on the Ceiling of Kitora Tumulus in Japan
The Kitora Tumulus in Nara Prefecture is a burial mound from the late 7th to early 8th century. Its stone chamber ceiling features an astronomical chart with about 350 stars connected by red lines, forming more than 74 Chinese-style constellations. It also depicts the sun, moon, and four circles: the inner circle, outer circle, ecliptic, and equator. It is considered the oldest existing ceiling star map in East Asia [9]. The number of stars varies by source, with some counting about 350 and others 277; here we use about 350.
The 28 lodgings are depicted on the ceilings of the Takamatsuzuka and Kitora Tumuli, suggesting they were transmitted to Japan during the Asuka period [2]. Thus, the Chinese star sky, personified as an emperor and officials, was painted on the ceiling of a Japanese tomb across the sea. Was this map drawn based on observations made in Japan? Several studies have calculated when and where the original observations were made by analyzing star and equator positions. Estimates for the date range from around the 1st century BC to around 300 AD, and locations vary between 38.4 degrees north latitude and 33.9 degrees north latitude. However, all studies conclude that the observations were made on the continent [10]. The Kitora astronomical chart is believed to have been drawn based on star maps transmitted from the continent, serving as a clue to the flow of scientific knowledge from Asia to Japan [10].
5. How the 28 Lodgings Appear in Japanese Life: The Kanji for "Subaru" and Calendar Notes
The kanji character for the star cluster "Subaru" (Pleiades) is said to have been assigned from the "Mao lodging" (Bou-shuku) of the 28 lodgings. The original Japanese name was "Sumaru" [2]. In Japan, the 28 lodgings were later used in calendar annotations (reki-chu). This shows that the concept, which began with the moon’s lodgings, continued to be used in different forms in Japan [2].
6. How to Investigate the Moon's Movement Among the Stars Yourself
On a night when the moon is visible, find the moon and a bright star near it from a window. Sketch their positions and write the date. If you look at the same time the next night, you can verify with your own eyes how the moon moves away from the star. Do not force it on cloudy days; try it on a clear night.
If you want to read more, the National Astronomical Observatory of Japan’s Calendar Wiki has an explanation of the 28 lodgings [2]. The Saitama City page on Edo-era astronomy explains the sidereal month and the 28 lodgings [1]. Both are available in Japanese.