Leidian

Authors: Boshun YANG, Susanne M Hoffmann

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Léi Diàn (Thunder and Lightning, 雷電) is a six-star Chinese asterism belonging to the outer asterisms of the Gan school. It lies south of Yingshi. Although modern reconstructions of its membership and outline vary, all major identifications place it in the present-day constellation Pegasus. This asterism might have been created in late Western Han. Its primary image is thunder and lightning. In the same sector of the sky, it forms a meteorological cluster with Pīlì (Thunderclap) and Yúnyǔ (Cloud and Rain).

Since August 2026, Leidian is also a modern IAU-star name; it refers to the star ρ Peg in Pegasus.

Concordance, Etymology, History

The two elements of the name already distinguished sound from light in early lexical thought. The Shuowen jiezi 說文解字explains the archaic graph 靁 as the movement caused when yin and yang press against one another, with 畾 evoking a revolving form; it defines 電 as the flash produced by the excitation of yin and yang. The Eastern Han Shiming釋名 gives phonetic glosses: thunder (léi) resembles the rumble of objects turning against an obstruction, while lightning (diàn) is so called because it vanishes as soon as it appears. These are not modern meteorology, but they show a clear conceptual pairing of two related yet distinct phenomena.

The Thunder Lord Beating a Drum in a Han-Dynasty Pictorial Stone Relief from Wubaizhuang, Linyi, Shandong

Because thunder is invisible, it was rendered through the tangible technology of the drum. In the Eastern Han Lunheng論衡, Wang Chong王充 reports that painters represented thunder as a string of connected drums and portrayed Leigong, the Thunder Lord, as a strongman pulling the drums with one hand and striking them with a mallet in the other. Wang’s purpose was to refute a literal divine-drum explanation, but his criticism preserves evidence for a visual convention: by the Eastern Han, the Thunder Lord, linked drums, and the striking mallet formed a recognizable image. The asterism thus stood between two modes of knowledge—natural interaction between yin and yang, and a materialized image of drums, divinity, and heavenly authority.

Identification of stars

Leidian underwent a substantial change in membership. Yang Boshun dates the major alteration to the Huangyou period (1049-1054 CE) of the Northern Song and distinguishes an early to Jingyou pattern from the Huangyou pattern; Yi Shitong’s Qing numbering represents another catalogue tradition influenced by European astronomy.

Star Names or Orders(Qing)	Han Dynasty (SUN X. & J. Kistemaker)	3rd to 6th Century (Boshun Yang)	Song Dynaty (Boshun Yang, 1034 CE)	Song Dynasty (Pan Nai, 1052 CE)	Song Dynasty (Boshun Yang, 1052 CE)	Qing Dynaty (Yi Shitong, 18th Century)
1st	σ Peg （determinative）	σ Peg （determinative）	σ Peg （determinative）	σ Peg （determinative）	σ Peg	ζ Peg (42 Peg)
2nd	ρ Peg	HIP 113445	HIP 113445	52 Peg	ρ Peg （determinative）	ξ Peg (46 Peg)
3rd	55 Peg	ρ Peg (50 Peg)	ρ Peg (50 Peg)	55 Peg	59 Peg	σ Peg (49 Peg)
4th	58 Peg	55 Peg	55 Peg	58 Peg	58 Peg	55 Peg
5th	66 Peg	58 Peg	58 Peg	66 Peg	66 Peg	66 Peg
6th	70 Peg	57 Peg	57 Peg	77 Peg	70 Peg	70 Peg

Maps (Gallery)

The configurations of Leidian depicted in the three early star maps share a common pattern, whereas the Suzhou star map, engraved in the thirteenth century during the Song dynasty, begins to show noticeable changes.

When European Jesuits in the late Ming dynasty (1630s) reidentified this asterism on the basis of European star catalogues, they not only assigned different constituent stars to it but also failed to reconstruct it in full, leaving three stars unaccounted for. Jesuits in the Qing dynasty restored the asterism to its full complement, although their identification of its stars had already diverged from the traditional one.

Moreover, although the star maps in the Xin Yixiang Fayao used by Pan Nai ultimately derive from the Song dynasty, they actually belong to a revised Qing-dynasty edition and therefore display a high degree of similarity to eighteenth-century versions.

Leidian

historical map	modern identification	same in Stellarium
Leidian inLeidian in Cheonsang Yeolcha Bunyajido	Leidian before Tang dynasty reconstructed by Boshun Yang	Leidian before Tang dynasty in Stellarium
Leidian in Dunhuang star map
Leidian in Gezi yuejin tu
Leidian in Xinyixiangfayao star map	Leidian in1052 （Huangyou reign of Song) reconstructed by Pan Nai	Leidian in 1052 (Huangyou reign of Song) by Pan Nai in Stellarium
Leidian in Suzhou star map	Leidian in 1052 (Huangyou reign of Song) reconstructed by Boshun Yang	Leidian in1052 （Huangyou reign of Song) by Boshun Yang in Stellarium
Leidian in Jianjie zongxing tu of 17th century
Leidian in Yixiang kaocheng star map of 18th century	Leidian in 18th century reconstructed by Yi Shitong	Leidian in 18th century in Stellarium

IAU Working Group on Star Names

In 2026, the name of the historical constellation "Leidian" was suggested to be used for ρ Peg in this constellation, for it is relatively brighter and was determinative star.

Decision: ...

References

References (Chinese)