This Month in Astronomical History: May 2020

Each month as part of this series from the AAS Historical Astronomy Division (HAD), an important discovery or memorable event in the history of astronomy will be highlighted. This month's guest author, Jason E. Ybarra, writes about the first recorded perihelion passage of Halley’s comet. Interested in writing a short (500-word) column? Instructions along with previous history columns are available on the HAD webpage.

First Recorded Perihelion of Halley’s Comet

Halley’s comet is the most well-known comet, with an orbit that returns to the inner part of the solar system every 75-77 years (see Figure 1). It is named after English astronomer Edmond Halley (1656-1742) who first suspected that the comets of 1531, 1607, and 1682 were the same comet and, in 1705, predicted it would return in 1758.^1,2 Subsequently, French astronomer Alexandre-Gui Pingré identified the comet of 1456 as an apparition of comet Halley, followed by French astronomer Paul-Auguste-Ernest Laugier who likewise linked the comet of 1378 from ancient Chinese astronomical records.^3,4 However, stepping further backward in time is not straightforward since the planets of the solar system perturb the comet’s path. It wasn’t until the beginning of the 20th century that the equations of motion were integrated backwards in time taking these perturbations into consideration. Philip Herbert Cowell and Andrew Claude Crommelin, who were among the first to take on this task, found the earliest date in Chinese records they could confidently identify with Halley’s comet to be 240 BCE.⁵ Cowell and Crommelin quote the following passage from the 1871 book Observations of Comets by John Williams (1797-1874):

In the 7th year of the reign of Che Hwang [240 BCE] a comet first appeared in the east. It was afterwards seen in the north. In the 5th moon [May] it was seen for 16 days in the west.

Williams, who was the assistant secretary of the Royal Astronomical Society, took it upon himself to create a complete catalog of comets from Chinese records by adding those missed in the catalog by Édouard Biot (son of physicist Jean-Baptiste Biot).⁶ In 1843 Biot published his catalog in the astronomical ephemerides Connaissance des Temps 1846, referencing a manuscript by astronomer Father Antoine Gaubil entitled Catalogue des Cometes Observees en Chine, held at the Paris Observatory.⁷ This manuscript is recorded as lost,^8,9 but excerpts from it exist in Alexander Guy Pingré’s Cométographie, published in 1783.

Father Antoine Gaubil (1689-1759) was a Jesuit missionary sent to Beijing (Peking) in 1721 and who stayed there until his death. He frequently corresponded with the Royal Society in England, sending his own astronomical observations and translations of ancient Chinese astronomical records. He also corresponded with astronomer Joseph-Nicolas Delisle, sending his revised history of Chinese astronomy for Delisle’s opinion before publication. It is from Delisle's collection of manuscripts that the Paris Observatory obtained Gaubil’s catalog. Gaubil’s source for comets before 1222 was the Chinese encyclopedia Wenxian Tongkao by Ma Duanlin published in 1319. The Wenxian Tongkao was also one of the sources Williams consulted for his catalog.

The Wenxian Tongkao, in turn, drew upon the Records of the Grand Historian or Shiji completed around 94 BCE by Han court astrologer Sima Qian¹⁰ (see Figure 2). It is organized into 130 scrolls systematically covering the history of China from the Yellow Emperor to the end of the second century BCE, biographies of emperors and other eminent persons, and treatises on various topics such as commerce and astronomy. In scroll six, the biography of the First Emperor of Qin (Ch’in), we find the passage about the 240 BCE comet:

In the seventh year (240 B.C.), a comet appeared first in the east, then in the north. In the fifth month^†, it appeared in the west … The comet appeared again in the west for sixteen days.¹¹

These observations are consistent with the known orbital parameters of Halley’s comet. Its orbit is retrograde and highly inclined (162°) with respect to the ecliptic. In the spring of 240 BCE, it would have appeared toward the east before dawn, day by day increasing in brightness, right ascension, and declination as it approached perihelion. After perihelion, the comet would have reappeared to the west in the evening. Thus, the comet of 240 BCE was observed before and after perihelion, making it the first recorded perihelion of comet Halley.

^† The traditional Chinese calendar begins the second new Moon after the winter solstice. For the year 240 BCE, the fifth month would have been between 24 May and 22 June in the Gregorian calendar.

References
1. Halley, E. 1705, “IV. Astronomiæ Cometicæ Synopsis, Autore Edmundo Halleio apud Oxonienses Geometriæ Professore Saviliano, & Reg. Soc. S,” Phil. Trans. R. Soc., 24, 1882-1899. https://royalsocietypublishing.org/doi/10.1098/rstl.1704.0064
2. Halley, E. 1705, A Synopsis of the Astronomy of Comets. London: John Senex. https://archive.org/details/synopsisofastron00hall/page/n3/mode/2up
3. Pingré, A.-G. 1783, Cométographie ou Traité Historique et Théorique des Comètes. Paris : Imprimerie Royale.
4. Laugier, P.-A.-E. 1843, “Notice sur l’apparition de la comète de Halley en 1378,” Comptes Rendus Hebdomadaires des Séances de l’Académie des Sciences, 16, 1003-1006
5. Cowell, P. H. & Crommelin, A. C. D. 1908, “The Perturbations of Halley's Comet in the Past. Fifth Paper. The Period B.C. 240 to A.D. 760,” MNRAS, 68(9), 665-668. https://doi.org/10.1093/mnras/68.9.665
6. Williams, J.1871, Observations of Comets: From B. C. 611 to A. D. 1640, Extracted from the Chinese Annals, Translated, with Introductory Remarks, and an Appendix Comprising Tables for Reducing Chinese Time to European Reckoning, and a Chinese Celestial Atlas. London: Strangeways and Walden.
7. Biot, E. 1843, “Catalogue Des Comètes Observées en Chine depuis l’an 1230 jusqu'à l’an 1640 de Notre ère,” In Connaissance des Temps ou des Mouvements Célestes à l'Usage des Astronomes et des Navigateurs, pour l’an 1846, Paris: Bureau Des Longitudes.
8. Lalande, J. J. 1803, Bibliographie Astronomique avec l'Histoire de l'Astronomie 1781-1802. Paris: De l'imprimerie de la République. pp 588-589.
9. Bigourdan, M. G. 1895, “Inventaire Général et Sommaire des Manuscrits de la Bibliothèque de l’Observatoire de Paris.” In M. F. Tisserand, ed. Annales de l'Observatoire de Paris: Mémoires. Tome XXI. Paris: Gauthier-Villars et Fils. pp F.1-F.60.
10. Violatti, Cristian. Sima Qian. Ancient History Encyclopedia. Retrieved from https://www.ancient.eu/Sima_Qian/
11. Ch’ien, S.-M.1994, The Grand Scribe's Records: Volume 1: The Basic Annals of Pre-Han China. Edited by W. H. Nienhauser, Jr., Translated from the Chinese by Tsai-fa Cheng, Zongli Lu, William H. Nienhauser, Jr., and Robert Reynolds. Bloomington: Indiana University Press.