Event #209: Guest Star, Comet Swift-Tuttle

The oldest source of Information for this comet was the Han shu (100). It reports a “guest star” was observed by the Chinese “at the northeast of Kuan-So [α, β, γ, δ, ε, θ, ι, π, and ρ Coronae Borealis] moving in a southerly direction” on -68 August 20 (probably August 20.5 UT). On August 27 it “entered the T’ien-Shih Enclosure [Hercules, Serpens, Ophiuchus, and Aquila], with its rays pointing toward the southeast.” The Chinese said the object was white.

109P/-68 Q1 (Swift—Tuttle) Discovered: -68 August 20.5 (Δ =0.64 AU, γ=0.99 AU, Elong.=70°) Last seen: -68 August 27 (Δ =0.64 AU, γ=0.98 AU, Elong.=69°) Closest to the Earth: -68 August 23 (0.6247 AU)Calculated path: HER (Disc), CrB (Aug. 21), HER (Aug. 25), OPH (Sep. 1)

A. G. Pingré (1783) began a trend with this comet when he incorrectly included the object of -68 July 23 with the observations. Subsequently, Benjamin Peirce (1846) computed an orbit using the observations gathered by Pingré and determined that the comet passed perihelion in -68 July.Not everyone was convinced that the objects seen in -68 July and August were the same. Around the time Peirce was working on the orbit, Édouard C. Biot was constructing a catalog of novae seen since ancient times. One of the objects in his catalog was the “nova” of -68 July 23. Several years later, Adolf Berberich made the suggestion that the July object might have been a meteor train. H. H. Kritzinger (1908) was led to the comet of -68 during his investigation of the orbit of comet C/1858 L1 (Donati). He noted the similarity between the orbits of comet Donati and the comet of -68, although he did acknowledge a 47° difference in inclination. Kritzinger considered the possibility that the July object was not related to the August object. He then tried to link the August -68 observations with comet Donati, but concluded identity was not possible. The comet of -68 came up again during an investigation into the orbit of comet 109P/Swift-Tuttle in 1972. In a private communication, I. Hasegawa suggested to B. G. Marsden that the -68 August observations might represent this comet and gave the likely perihelion date as August 25. A paper published by Marsden in 1973 concludes that the August observations represented the “only really good candidate for [a previous apparition of] P/Swift-Tuttle,” while the July comet must be a separate comet. Marsden added that 17 revolutions of 109P/Swift-Tuttle probably occurred between this apparition and that of 1862. Hasegawa (1979) later revised the perihelion date to -68 August 26±1. After the recovery of 109P/Swift-Tuttle in 1992, the link with the August object of -68 was confirmed. Calculations by Graeme Waddington and Marsden an orbit with a perihelion date of -68 August 27.5. In a paper published in Icarus in 1993, Marsden, G. V. Williams, G. W. Kronk, and Waddington presented details of the observational history of Swift-Tuttle, including this apparition.

full Moon: August 4, September 3

69 BC, August 20, China. A guest star was seen at the northeast of Corona Borealis moving in a southerly direction. On August 27 it entered the region near southern Hercules with its white tail pointing southeast.

1st year of the Dijie reign period of Emperor Xuan of the Han Dynasty, 6th month, day bingyin [3]; a guest star reappeared northeast of Guansuo, moving southward, until the 7th month, on the night of day guiyou [10], when it entered Tianshi, its rays of flame pointing southeast and its color was white.