Event #107: Comet Halley observed in Babylon and China

Various orbital investigations have shown that 1P/Halley passed perihelion during the first days of August in -86. Such widespread agreement indicates the orbit is well determined and, when this is combined with the scant observations from China and Babylon, a good picture of this apparition is derived.

The oldest source of information for this comet is the Babylonian cuneiform tablet designated BM 41018. During the early 1980s Hermann Hunger identified a fragment of text that referred to a comet, and, in 1985, F. R. Stephenson, K. K. C. Yau, and Hunger were able to use additional astronomical references on the same Babylonian tablet to establish the year as -86. They were also able to establish that the comet was seen “day beyond day” during lunar month of July 14 to August 11, and that another observation on August 24 reveals the comet had a tail 10° long.

The Chinese text Han shu (100) contains another observation of this comet. It says a “sparkling star” was seen “in the eastern quarter” during autumn, sometime within the month of August 10 to September 8.

The orbit below was computed by Donald K. Yeomans and Tao Kiang (1981) and indicates the comet reached a maximum solar elongation of 51° on July 8, and its most northerly declination of +43° (apparent) on the 25th. The comet moved to within 21° of the sun on the 28th. It is very likely that the comet was found prior to this conjunction with the sun, as Yeomans, Jürgen Rahe, and Ruth S. Freitag (1986) indicated the comet was probably brighter than magnitude 3 after mid-July and probably close to magnitude 1.4 at the time of the conjunction. But a problem also surfaces as there is a contradiction in the Chinese observation: the comet was in the morning sky in the east prior to this conjunction with the sun, not after. Kiang (1972) commented that “either the month or the direction … is wrong.” Following up on this, Stephenson and Yau noted that if the Chinese month was changed from 7th (August 10 to September 8) to the 6th (July 9 to August 9) the direction would fit. But they then noted that the character for the 6th and 7th months were dissimilar, so that the direction adjustment suggested by Kiang might be the more likely alternative.

After the conjunction, the comet would have entered the westen sky and the solar enlongation would have increased to 36° by August 12. Thereafter, the comet would habe again dived into twilight, passing only 0.5° from the sun on September 28. Because of the declining elongation, Stephenson et al. have suggested the August 24 date probably marked the final observation of this comet. Because of the evening sky location, the probable UT was August 24.7.

P. H. Cowell and A. C. D. Crommelin (1908) were the first to link the comet of -86 to 1P/Halley. Their computations revealed a probable perihelion date of -86 August 15. Later investigations were conducted by Kiang (1972), Yu-Che Chang (1979), Yeomans and Kiang (1981), J. L. Brady (1982), Werner Landgraf (1986), and G. Sitarski (1988).

Absolute Magnitude : H 10 = 5.0 (Kronk)

Full Moon : July 25, August 24

Sources Han shu (100), 7:1b; A.G. Pingré (1783), pp 274-5; J. Williams (1871), p. 7; G. F. Chambers (1889), p. 555; MNRAS, 68 (Supp. 1908), pp 665-70; Ho Peng Yoke (1962), p. 145; MRAS, 76 (1972), pp. 35, 56; CAA, 3 (1979), pp. 124, 127; D. K. Yeomans and T. Kiang (1981), p. 642; J. L. Brady (1982), p. 210; JBIS, 38 (1985), p. 201; Nature, 314 (1985 Apr. 18), pp. 587-92; W. Landgraf (1986), p. 258; JRASC, 80 (1986 Apr.), p. 72; G. Sitarski (1988), p. 263; VA, 34 (1991), pp. 180, 183.

Comet Halley. A medieval Chinese encyclopedia states that a bushy star comet appeared in the east during the month from August 10 to September 8. Kiang (1972) notes that Halley would have been seen in the west during that time and suggests that the month may have been incorrectly transcribed in the secondary Chinese source. The comet would have been seen in the east in the previous month. Since the motion of Comet Halley in 87 BC is quite well established from orbit extrapolations, it seems likely that it was indeed the one referred to in the Chinese medieval source. Stephenson et al. (1985) note that according to Babylonian records, a comet was visible “day beyond day” during the lunar month July 14 to August 11, and a reasonable interpretation of those records suggests that the come was last seen on August 24. The motion of the comet as given by Yeomans and Kiang (1981) indicates that its solar elongation on August 24 was only 31 degrees and decreasing with time. The Babylonian account also records the first quantitative measurement of comet Halley’s tail noting that it was observed to be 4 cubits long, or approximately 10 degrees.