Ballochroy and Kintraw Controversial Sites

The site of Ballochroy in Argyll (western Scotland) now consists of a row of three stones with the flat faces, most unusually, across the row. A small cist is the only surviving remnant of a former large cairn or burial mound. There were once two small cairns and another standing stone in the same alignment (Burl 1993, p. 176). The alignment to the southeast (A ~ 226°) passes over the islet of Cara and would have marked the sunset at the winter solstice [8 = -23.06°; Ruggles (1984, p. 279) finds declination limits -25.5 to -24.5°]. Looking across the flat sides of the stones, one would have seen the Paps of Jura across the sea in the distance, with Corra Bheinn mountain marking the summer solstice sunset. To the northeast, along an elevated horizon, the line marks the extreme northerly position of the Moon (moon-rise at major standstill). Burl (1993, p. 177) wrote

The sightline towards Jura and the midsummer sunset was uninterrupted, and knowing that the wide faces of the slabs were atyp-

ically angled across the row it is likely that the builders of the row quite deliberately set them transversely to establish the alignment, unaware of the lucky coincidence that theirs was the lone latitude in Britain where the midwinter and midsummer solstices occurred at right angles to each other. A few degrees to the north or south would have rendered a comparable design unworkable.

The view would seem to be only slightly exaggerated. At an epoch such as 1750 b.c., when 8 = 23.90° (Thom 1971/1978, p. 42), one finds that the site where twice the amplitude on a flat horizon is 90° has a latitude of 55.0°. For the given latitude of the Ballochroy site, 55°42'44" (Thom 1971/1978, p. 37), summer and winter solstice azimuths of sunset, are, respectively, ASS = 315.99, AWS = 224.01, so that their difference is ASS - AWS = 91.97°, again for a flat horizon. However, the horizon is not flat. Thom (1971/1978, p. 42) assumed that the alignment of the Ballochroy cist to the rolling slope of Corra Bheinn was the intended alignment to midsummer sunset and that the alignment from Ballochroy to the Isle of Cara was intended to mark midwinter sunset. The differences between these two measured azimuths, 316°05' - 226°16', is 89°49'. Thom's analysis of this (and related sites) considers the effect of the elevation of the horizon and refraction and with a corrected true altitude of setting. From Ballochroy, he derived a value for the obliquity: 23°54'.2 ± 0'.7, and from this a date: 1750 ± 100 b.c. Burl's "coincidence" statement requires a range of dates to be meaningful, but if Thom's analysis is correct, and if the site were in fact erected ~1750 b.c., it seems to us extremely unlikely that the builders who followed this atypical procedure would not know that they were at a place where it would work.

To the North, at Kintraw, there is a site that has been the subject of a major controversy. In a field, there is a cairn with a posthole in it and a very tilted standing stone. Most unusually, the cairn is not a burial mound. The stone does not seem to be aligned on anything that would have been visible at the site from ground level. However, Thom suggested that it was aligned to a notch created by the profiles of two mountains, one of which was Corra Bheinn in the Paps of Jura (the same one aligned from Ballochroy, nearly 30 miles to the SW). The midwinter setting Sun might have been visible for a moment or two from the top of the cairn (at A = 224°), but the cairn would need to have been higher than it is at present, or the observer would need to have been tall. In fact, the placement of the cairn could have been made without seeing the Sun from this site, if the site line were established with other markers.

On examining the site, Thom found a ledge on a slope from which the Sun could have been seen, and the location of the cairn established. Euan MacKie (1976) realized that the archaeoastronomical usage of the ledge was a hypothesis that could be tested archaeologically, and he tried to do so. He found that there were two boulders placed so that an observer looking between them would see the notch and a line to the notch would pass directly over the cairn. He then excavated the ledge on which the boulders rested, but found only indirect evidence that the site was artificial.22 Contro

22 A stone layer that extended upstream from the boulders appeared to be artificial in terms of location and in the orientation and dip of the stones themselves.

versy developed concerning the visibility of the notch on Jura and the necessary height of an observer to see the notch from the platform (MacKie 1976, 1981; Patrick 1981; McCreery, Hastie, and Moulds 1982). The conclusion of McCreery et al. (1982) was that an observer would always have had to be taller than 5' and that the amount of foliage on intervening trees could have obscured the view for an observer under 5*7". Refraction variations, inherently unpredictable, would have contributed to the visibility problem. Whatever the validity of these criticisms for the epoch when the site was in use, the notch is plainly visible in a photograph published by MacKie (1976).

Another aspect of controversy involved the width of the ledge. MacKie (1976) claimed that the ledge was wide enough to observe the Sun for some days before and after the solstice. According to McCreery et al. (1982, pp. 187-198), the ledge is not wide enough. They attribute the MacKie claim to a confusion between the azimuth change caused by a declination change and that of the declination. We will discuss the use of a platform at Kintraw for precise observations of the Sun near the end of §6.2.15, after we describe Thom's proposed observing method, and compute the necessary distance that would have been stepped by an observer to see the shifted azimuth caused by the changing declination of the Sun and Moon.

From the cairn, the lunar 9' perturbation (see §3.4.5) could have been detected as the Moon set at minor standstill among the complex silhouette of the hills of Jura (Thom 1971/1973/1978, p. 39). The possibility that such precision could be obtainable in the megalithic is, well, incredible, and it is not surprising that many investigators have refused to believe it. In the next few sections, however, megalithic constructs are described that make it at least possible that the necessary information was indeed encoded in the monuments.

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