Beiluo Shimen

Authors: Lyu Haocheng

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Beiluo Shimen and Tiangang in Stellarium

Beiluo Shimen

Asterism Info
Native	北落師門
Romanisation	Běi Luò Shī Mén
IPA	/peɪ˨˩˩.lwo˥˩.ʂɻ̍˥.mən˧˥/
Translation	Gate of the Northern Military Camp
Position (2000)
Right ascension	344.4076667
Declination	-29.62519444
Area	0 sq. deg.
Stars
Bright stars	1
Bayer/Flamsteed stars	1
Stars brighter than 3.00m	1
Brightest star	α Psc (1.16m)
Taxonomy
category of asterism	constellation
IAU- constellations	PsA

Běi Luò Shī Mén (北落師門, Gate of the Northern Military Camp) is a traditional Chinese asterism belonging to the Shi (室) mansion, the sixth of the seven mansions of the Black Tortoise of the North in the Twenty-Eight Mansions system. Among the Three Schools of ancient Chinese astronomy, it is classified as a Shi School asterism (石氏星). The asterism consists of a single star located southwest of Yǔlínjūn (羽林軍, Palace Guard). In modern constellation boundaries, Beiluo Shimen lies within Piscis Austrinus (the Southern Fish), corresponding to the star α Piscis Austrini (Fomalhaut).

Concordance, Etymology, History

Etymology

The name "Běi Luò Shī Mén" (北落師門) originally comprised two separate names: "Běi Luò" (北落) and "Shī Mén" (師門), with "Shī Mén" used as an alternative name for "Běi Luò". In many texts, "Běi Luò" appears as a shortened form of the full name.

The Book of Jin, Treatise on Astronomy (Jin Shu·Tianwen Zhi, 晉書·天文志) provides the following explanation of the name:

"Běi" (北, North) means that this asterism is located in the north; "Luò" (落) means the fence or barrier (藩落, fānluò) of heaven; "Shī" (師) means a multitude; "Shī Mén" (師門) thus means the military gate. The north gate of Chang'an city was called 'Běi Luò Mén' (北落門), named after this asterism .It governs unusual omens and is used to observe military movements.

In other words, the four characters can be interpreted individually as follows:

• Běi (北, "North") — indicates that the star is located in the northern sky, belonging to the Shi (室) mansion of the Northern Black Tortoise (北方玄武) in the Four Symbols system (四象, sì xiàng).
• Luò (落) — means the outer fence or barrier of a city or military camp.
• Shī (師) — means a multitude, and by extension, an army.
• Mén (門, "gate") — together with Shī, forms Shī Mén (師門), meaning "military gate."

Beiluo Shimen thus symbolizes the gate of the northern military encampment, guarding the northern frontier. The north gate of Han Chang'an was called the "Běi Luò Mén" (北落門, also known as Luò Chéng Mén, 洛城門), a name derived directly from this asterism.

The "Reddish Star"

The Kaiyuan Zhanjing (開元占經) describes the asterism:

To the southwest of Yǔlín (羽林) there is a large reddish star (大赤星), shaped like Dàjiǎo (大角, Arcturus (Ἀρκτοῦρος)). It is the gate of the celestial army, named "Běi Luò", also called "Shī Mén".

α Piscis Austrini (Fomalhaut) is not a red star but a white main-sequence star. The description of it as a "large reddish star" (dà chì xīng, 大赤星) has been interpreted in several ways:

1. Atmospheric effect: Fomalhaut's declination is very far south, causing it to appear only low in the southern sky. Due to the precession of the equinoxes, in ancient times it appeared even lower than today. Atmospheric refraction and extinction near the horizon may have caused it to appear reddish.
2. School affiliation: Beiluo Shimen is a Shi School asterism. In traditional Chinese star charts, different schools were often distinguished by colour — with red used to mark Shi School stars. The description may thus indicate its affiliation with the Shi School rather than its actual colour.

The Celestial Military Encampment

In addition to Beiluo Shimen, there are two other asterisms in the Chinese system representing "military camp gates": Jūn Nán Mén (軍南門, Southern Military Gate) of the Gan School (甘氏), located near Tiān Dà Jiāngjūn (天大將軍, Celestial Great General); and Jūn Mén (軍門, Military Gate) of the Wu Xian School (巫咸氏), located near the Zhěn (軫, Chariot) mansion.

Beiluo Shimen was placed to the southwest of Yǔlínjūn (羽林軍, Palace Guard). Together with the surrounding asterisms — Lěi Bì Zhèn (壘壁陣, Line of Ramparts), Yǔlínjūn (羽林軍, Palace Guard), and Tiān Gāng (天綱, Celestial Military Tent) — Beiluo Shimen forms a complete northern celestial military encampment: the ramparts (Lěi Bì Zhèn) surround the camp, the Palace Guard (Yǔlínjūn) mans the defences, the Gate (Běiluò Shīmén) serves as the main gate of the camp and controls access, and the Emperor's Tent (Tiān Gāng) stands nearby, just outside the encampment.

Identification of stars

The identification of Beiluo Shimen has been consistent throughout history: it has always been α Piscis Austrini (Fomalhaut). No changes or alternate identifications are recorded in any historical star catalogues.

Star Names or Orders(Qing)	Han Dynasty (SUN X. & J. Kistemaker)	before Tang dynasty: 3rd to 6th Century (Boshun Yang)	Song Dynaty: Huangyou, 1052 (Pan Nai, based on Xinyixiangfayao Star Map)	Yuan dynasty: 1279-1368 (Pan Nai)	Qing dynasty: 18th Century (Yi Shitong)	Ho PENG YOKE
Beiluo Shimen	α PsA	α Psc	α Psc	α Gru	α PsA	α PsA

Maps (Gallery)

historical map	modern identification (Yang 2023)	same in Stellarium
Beiluo Shimen (left) and Tiangang (right) in Cheonsang Yeolcha Bunyajido	Tiangang and Beiluo Shimen before Tang Dynasty Reconstructed by Boshun Yang(2023)	Beiluo Shimen and Tiangang before Tang Dynasty in Stellarium
Beiluo Shimen (left) and Tiangang (right) in Gezi yuejin tu
Beiluo Shimen (left) and Tiangang (right) in Xinyixiangfayao star map	Beiluo Shimen and Tiangang in Northern Song Dynasty (based on 1052 obserrvation) Reconstructed by Pan Nai (2009)	Beiluo Shimen and Tiangang 1052 (Huangyou reign of Song) by Pan Nai in Stellarium
Beiluo Shimen (left) and Tiangang (right) in Xianglin, a 17th-century non-official star map	Beiluo Shimen and Tiangang in late Yuan Dynasty (1363 or so) Reconstructed by Boshun Yang (2023)	Beiluo Shimen and Tiangang in late Yuan Dynasty (1363 or so) in Stellrium
Beiluo Shimen (left) and Tiangang (right) in Yixiang kaocheng star map of 18th century	Beiluo Shimen and Tiangang in 18th century reconstructed by Yi Shitong	Beiluo Shimen and Tiangang in 18th Century in Stellarium

IAU Working Group on Star Names

Since α Piscis Austrini is already officially named Fomalhaut by the IAU, the name "Beiluo Shimen" will not be adopted as an international name for this star.

References

References (Chinese)