Tianji

Tiān Jì (Celestial Discipline, 天紀) consists of nine stars forming an east–west alignment that extends across the modern constellations Corona Borealis, Hercules, and Lyra. This asterism and the coordinate of its determinative star was first recorded in the Western Han Shishi xingjing (Master Shi’s Star Canon, 石氏星經).

Concordance, Etymology, History

Tianji is also called Jì xīng (Decipline Star). The term jì (紀) originally denoted “a thread of silk,” later acquiring the metaphorical meanings of “order,” “law,” or “discipline.” Hence, the Shishi zan (Commentary of Shi) explains: “The nine stars of Tiān Jì regulate litigation.” The ancients believed that by observing this asterism, one could divine whether the legal order of the empire remained upright and just.

Another interpretation, however, regarded the nine stars of Tianji as representing the Nine States (which are the major component of ancient China). According to this view, any unusual phenomenon observed in the asterism—such as brightening, dimming, or disappearance—portended terrestrial disasters such as earthquakes or mountain collapses.

Because most of its component stars are faint, the ancient astronomers considered any abnormal changes in their visibility—whether excessive brightness, darkness, or disappearance—as inauspicious omens.

Identification of stars

Star Names or Orders(Qing)	Ho PENG YOKE	Yi Shitong Based on catalogue in 18th century	Pan Nai based on Huangyou Star Catalogue and Xinyixiangfayao Star Map	SUN X. & J. Kistemaker Han Dynasty	Boshun Yang before Tang dynasty	Boshun Yang Yuan Dynaty (1363)
1st/Determinative	upsilon CrB	xi CrB	xi CrB	xi CrB	xi CrB	zeta Her
2nd	xi CrB	zeta Her	nu2 Her	zeta Her	nu1 Her	53 Her
3rd	zeta Her	epsilon Her	zeta Her	53 Her	zeta Her	epsilon Her
4th	53 Her	d Her	epsilon Her	epsilon Her	epsilon Her	u her
5th	epsilon Her	61 Her	d Her	d Her	d Her	w Her
6th	d Her	u her	w Her	u her	u her	HIP 85382
7th	c Her	Her 86178	HIP 85382	theta Her	theta Her	theta Her
8th	u her	?	theta Her	kappa Lyr	kappa Lyr	HIP 88836
9th	theta Her	theta Her	f Her		mu Lyr	kappa Lyr

Maps (Gallery)

historical map	modern identification	same in Stellarium 25.3
Bagu in Cheonsang Yeolcha Bunyajido	Bagu before Tang Dynasty Reconstructed by Boshun Yang (2023)	Bagu before Tang dynasty demonstrated in Stellarium
Bagu in Suzhou Star Map	Bagu in Song Dynasty Reconstructed by Pan Nai (2009)	Bagu in Song dynasty demonstrated in Stellarium
Bagu in Jesuits Star Map in 17th Century	Bagu Reconstructed by Yi Shitong (1981) based on Qing Star Catalogue in 18th Century	Bagu in 18th century demonstrated in Stellarium

Star Name Discussion (IAU)

In 2025, the name of the historical constellation Bā Gǔ (八穀) was suggested to WGSN to be used for one of the stars in this constellation based on a review of Chinese cultural astronomy literature. Discussion focused on the bright star Delta Aurigae, which was the determinative star following multiple published versions of the asterism.

WGSN adopted the name "Bagu" for the bright star designated Delta Aurigae (HR 2077, HD 40035, HIP 28358) on 12 November 2025.

Bagu is a bright (V=3.72 mag) star at distance 43 parsecs. Since the middle of the 20th century, the star served as a Morgan-Keenan spectral standard for K0 giants. The star has a diameter about 12 times larger than that of our Sun. The star is a single-lined spectroscopic binary catalogued in SBC9, i.e. it has a faint companion on a period of 3.51 years (Griffin 2009). Specifically the name is applied to the primary Aa.

References

References (Chinese)