Stone and star gazing

Great Stone Circles - Astronomy in Prehistoric Britain and Ireland

Owen Gingerich welcomes the ascendancy of archaeo-astronomy.

With these two important but very different volumes, archaeo-astronomy of the British Isles has come of age. Both are ingeniously, almost ingenuously, arranged to disguise the significance of their central themes.

Aubrey Burl's splendidly illustrated contribution to British archaeology might pass as a Christmas coffee-table book. Actually it is a book about Stonehenge, full of convincingly argued revisionist views about that famous monument: "neither British nor a stone circle", and certainly not an observatory.

Although Clive Ruggles's book is large enough to decorate the coffee table, it is not at all the impulse purchase for Boxing Day. It is, in Darwin's words, "one long argument", a systematic account of the years of fieldwork that have demolished the late Alexander Thom's claims for precision megalithic astronomy and replaced them with a far more nuanced and culturally aware appreciation of the British and Irish stones.

To set Stonehenge in context, Burl describes seven other notable stone rings and one of wood, carefully chosen and arranged to intrigue and instruct the reader. The dilapidated and decaying Rollright Stones, 20 miles north of Oxford, rich in lore and fantasy, provide the starting point. "Seven long strides shalt thou take, and/If Long Compton thou canst see/King of England thou shalt be" are lines from a witch, luring an ambitious man to a stony doom. Burl recounts the legends, clearly taking a sly delight in puncturing any claims to antiquity. Next comes the enormous Cumbrian ring and outlier, Long Meg and her Daughters, and an occasion to discuss possible astronomical alignments. Long Meg stands in the direction of the midsummer sunset, and such a placement could well have been intentional. To have found such a solar line is not a surprise, Burl declares; what was unexpected was to find the stele carved with rings and spirals, "like a celestial advertisement".

To introduce the idea of associated avenues, Burl moves the scene to Somerset, to the rings at Stanton Drew. Next he chooses four rings in western Cornwall, including one almost totally destroyed, to illustrate the degradation of the sites as well as to deflate more legends. Finally there is Woodhenge, not all that far from Stonehenge, but a site that only excavations could reveal: "blandly anonymous, visually uninteresting ... yet holding vivid glimpses of its strange prehistoric world". Woodhenge is essential to Burl's account precisely because it was not a stone circle. He wishes to establish that stone was a comparative rarity on the chalks and clays of Wiltshire, that the ancient denizens were workers in wood, not in stone, and that when they came to build Stonehenge, they adapted their woodworking techniques to a stone monument unlike any other stone circle in the British Isles.

With these rings as background, Burl has laid the foundation for his heavy revision of Stonehenge orthodoxies. As is well known, Stonehenge is composed of two types of stones, the huge sarsens - a type of sandstone boulder moved 20 back-breaking miles from a region 18 miles to the north - and the smaller, three to six-ton, less conspicuous bluestones - a coarse basalt that is found in the Preseli Ridge in the southwestern tip of Wales. Archaeologists have argued that the bluestones were transported over 200 miles by land and sea, a view Burl says is "as fanatical as the fanaticism of the prehistoric carriers who supposedly performed that task". He counters quite persuasively that the bluestones were glacial erratics systematically collected by the later Stonehengians who added them to the existing structure. As for Stonehenge not being a British stone circle, Burl argues that the horseshoe configuration of the huge so-called trilithons is an import from Brittany, and hence not British, and he reasons that their mortise-and-tenon construction is the work of carpenters, not of masons, so that it cannot be classed as a stone ring. So much for vocabulary.

The idea that the midsummer sun rises over the heel stone is dismissed as only "ignorance and bigotry". The photographs showing the sun sitting neatly on the point of the heel stone have been "adjusted" by the photographer moving a foot or two sideways. Since Burl argues elsewhere that the sightlines in megalithic monuments are none too precise, it seems that here he protests too much. He includes an instructive diagram of the horizon and heel stone, showing that the moonrise at northernmost midswing lies south of the midsummer sunrise, a point that will baffle most astronomers because he gives no explanation of the fact that the moon's geocentric parallax moves it southwards. Burl treats with almost complete silence Gerald Hawkins, the astronomer who did the most to popularise the astronomical alignments at Stonehenge in his 1966 book Stonehenge Decoded , simply quoting: "An eclipse of the moon or sun always occurred when the winter moon - that is, the full moon nearest the winter solstice - rose over the heel stone." He makes no comment, as if the statment is too ridiculous to require any commentary, but the unexplained difference between the midsummer sunrise to the left of the heel stone and the midswing moonrise over the heel stone makes Hawkins's statement correct.

The many solar and lunar alignments proposed by Hawkins and others for Stonehenge, and the high-precision alignments elsewhere espoused by Thom in the 1970s, have by now fallen out of favour with the vast majority of archaeo-astronomers. This is largely the consequence of the systematic fieldwork undertaken by Clive Ruggles and his colleagues. Ruggles's new account is largely a well-organised recital of the series of projects targeted on specific questions, to be answered by data from selected groups of monuments. His account is buttressed by numerous charts, maps, tables and photographs conveying his hard-won data.

I was delighted to find myself quoted at the top of chapter two: "In 1977 I visited [Callanish, Kintraw, Ballochroy, Temple Wood (Kilmartin) and Brodgar]. These sites proved psychologically devastating to my tentative acceptance of precision astronomy in ancient Britain ... By focusing his attention on the specific astronomical sightlines, Thom neglected to inform his readers of the richer archeological context of many of the megaliths." Ruggles proceeds to present Thom's extensive results on astronomical sightlines, but then moves on to his own independent survey of 300 western Scottish sites, undertaken between 1979 and 1981.

By considering not only the distant horizon notches in the direction of the predetermined astronomical sightlines, but those elsewhere on the horizon, Ruggles and his co-workers demonstrated that Thom's claims would not stand up to unbiased statistical examination. This was the beginning of the end for precision astronomy in ancient Britain.

Ruggles lays out his investigations in largely chronological order, thereby presenting the reader with the history of these ideas during the past two decades. The reader peers over the shoulder of an astronomer-turning-archaeologist, and watches the slow and sometimes tedious accumulation of evidence in carefully conceived field programmes.

In 1981 the fieldwork turned to a different group of monuments, the rings that included a large megalith lying on its side. These recumbent stone rings are concentrated in the Grampian region of eastern Scotland. Burl's earlier researches had suggested that the stones had a ritual significance associated with the moon, a conclusion supported by the new, statistically controlled survey. Having abandoned the idea of precision astronomical alignment, Ruggles decided to ask whether rows of stones actually pointed to anything else, that is, possibly significant details along the horizon itself. For this research, in 1991 he chose to examine stone rows in southern Ireland, and later he re-examined data assembled in 1984 in western Scotland. The surprising result was that stone rows that are superficially quite similar yielded rather different results in the two locations. Whereas in Ireland the stone rows tended to point to conspicuous distant hilltops, this was much less clear in Scotland. Nevertheless, both groups seemed to have some relationship to directions where the moon could be found.

Meanwhile, in the late 1980s, with occasional help from a team of Earthwatch volunteers, Ruggles attempted to answer a question with a more archaeological focus: apart from possible astronomical alignments, are the sites themselves specially situated in the larger environment? Naturally this was a more challenging question to answer definitively without circular arguments. The result, fragile but persuasive, is that the ability to view a distant mountain (for example) entered the choice of locations. Nevertheless, rough astronomical alignments also seem to play a role. Archaeo-astronomy has not vanished, but has reached a new maturity.

Backed by the years of fieldwork meticulously reported in his book, Ruggles now plays the role of the sceptical astronomer. But, he reminds us, astronomy is an integral part of anthropological cosmology. To ignore astronomy in attempts to understand people's perceptions in the megalithic landscape is to impose another 20th-century agenda, one rooted in backlash to the astronomical overload of the 1960s and 1970s, understandable but nonetheless unreasonable. Archaeologists ignore astronomers at their peril.

Owen Gingerich is an astronomer and historian of science at the Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, United States.

Great Stone Circles: Fables, Fictions, Facts

Author - Aubrey Burl
ISBN - 0 300 07689 4
Publisher - Yale University Press
Price - £19.99
Pages - 200

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