Tianyue

Authors: Lyu Haocheng, Susanne M Hoffmann

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Tianyue in Stellarium

Tianyue (天籥)

Asterism Info
Native	天籥
Romanisation	Tiān Yuè
IPA	/tʰjɛn˥.ɥɛ˥˩/
Translation	Celestial Keyhole
Position (2000)
Right ascension	... to ...
Declination	... to ...
Area	xx.xx sq. deg.
Stars
Bright stars	8
Bayer/Flamsteed stars	4
Stars brighter than 3.00m	0
Brightest star	HIP 88839 (4.56m)
Taxonomy
category of asterism	constellation
IAU- constellations	Sgr

Tiān Yuè (天籥, Celestial Keyhole) is a Chinese constellation belonging to the Dou (Dipper) lunar mansion. Among the Three Schools of ancient Chinese astronomy, it is classified as a Wu Xian asterism. The asterism consists of 8 stars located west of the second star in the handle of the Southern Dipper (λ Sgr), at the border between Sagittarius and Ophiuchus.

Concordance, Etymology, History

Name and Symbolism

The character 籥 (yuè) is the original form of 钥 (yào), meaning a lock or key. Tian Yue is also written as Tian Yao (天钥), both meaning "the celestial lock and key". The ancients believed that this asterism governed the functions of opening and closing, hence its name.

Astronomical Position and Historical Significance

The placement of Tian Yue is closely connected to the Southern Dipper (Nandou (南斗)). The Southern Dipper is one of the Twenty-Eight Mansions, which are distributed along the ecliptic—the path traversed by the Sun, Moon, and Five Planets. The Southern Dipper lies precisely at the intersection of the ecliptic and the Milky Way, granting it a special status in the celestial system.

This region lies within the Milky Way, and asterisms located in the Milky Way were often conceived as ferries or fords (for example, Tianjin (天津), the Celestial Ford). Tian Yue is situated in a region called "Ximu zhi Jin" (析木之津, "the Ford of Ximu"). Ximu is one of the Twelve Xingci (十二星次 / Twelve Divisions), a Chinese system of dividing the celestial sphere into twelve segments by right ascension, based on Jupiter's orbital period (approximately 12 years) rather than on fixed asterisms like the Western zodiac. The Erya, Shitian (尔雅·释天 / Erya: Explanation of Heaven) records:

"The Ford of Ximu (析木之津) is Hanjin (汉津) between Ji (箕, Winnowing Basket) and Dou (斗, Southern Dipper)."

Here, "Hanjin" refers to the ford of the Milky Way. The Guoyu (国语 / Discourses of the States) records the celestial omens at the time of King Wu's conquest of the Shang dynasty around 1046 BCE:

"Jupiter was at Chunhuo (鹑火, approaching the constellations of Hydra and Leo), the Moon was at Tiansi (天驷, the Room mansion), and the Sun was at the Ford of Ximu."

This demonstrates the great importance ancient China attached to this region—the passage of the Sun, Moon, and planets through this area was often used to mark significant historical events.

Function and Symbolism

Because of the special significance of the Southern Dipper's position, the ancients regarded it as "Tian zhi Duguan" (天之都关, "the metropolitan pass of Heaven")—a celestial gateway through which the Sun, Moon, and Five Planets had to pass. Tian Yue was the key that controlled the opening and closing of this gate. In the night sky, the asterisms of Nandou (南斗) (Southern Dipper), Tian Yue, Jian (建) (Establishment), and Gou (Dog) together form the complete image of a celestial pass.

It is worth noting that the Milky Way and the ecliptic intersect at two points on the celestial sphere: one is located near Tian Yue, and the other is at Dongjing (东井, the Well mansion). On that opposite side, Dongjing, together with Tianguan (Celestial Pass), Nanhe (Southern River) and Beihe (Northern River), likewise forms a pass-like asterism configuration.

Identification of stars

Star Names or Orders(Traditional/Qing)	Ho PENG YOKE	Yi Shitong Based on catalogue in 18th century	Pan Nai based on Xinyixiangfayao Star Map	Boshun Yang before Tang dynasty	Boshun Yang Song Jingyou(1034)
1st	63 Oph (HIP 87706)	63 Oph (HIP 87706)	4 Sgr (Determinative)	4 Sgr (Determinative)	7 Sgr
2nd	HIP 87099	-	1 Sgr	1 Sgr	1 Sgr (Determinative)
3rd	58 Oph	58 Oph	70 Sgr	70 Sgr	70 Sgr
4th	-	HIP 86352	HIP 89678	HIP 89678	HIP 89678
5th	52 Oph	52 Oph	HIP 88839	HIP 88839	HIP 88839
6th	51 Oph	51 Oph	HIP 88012	HIP 88012	HIP 88012
7th	HIP 85783	HIP 85783	HIP 87836	HIP 87836	HIP 87836
8th	3 Sgr	3 Sgr	63 Oph (HIP 87706)	63 Oph (HIP 87706)	63 Oph (HIP 87706)

Maps (Gallery)

historical map	modern identification (Yang 2023)	same in Stellarium 24.4
Tianyue in Cheonsang Yeolcha Bunyajido	Tianyue before Tang Dynasty reconstructed by Boshun Yang (2023)	Gouguo before Qing Dynasty in Stellarium
Tianyue in Suzhou Star Map	Tianyue in Song Dynasty (Huangyou period) reconstructed by Pan Nai (2009)
Tianyue in Yixiang Kaocheng Stat Map (18th century)	Tianyue in Qing dynasty reconstructed by YI Shitong based on Yixiang Kaocheng Star Catalogue (18th century)	Tianyue in Qing dynasty (18th century) in Stellarium.

IAU Working Group on Star Names

In 2026, the name of the historical constellation "Tianyue" was suggested to be used for one of the stars in this constellation. The star 4 Sgr was recommended, as it is the historical determinative star of the asterism and lies closest to the intersection of the ecliptic and the Milky Way, aligning well with the asterism's symbolic meaning.

Decision: ...

References

References (Chinese)