NE Cairn; half an hour before sunset [photo: Ian B. Wright, 2009] 

IBW Clava 6A bRight

Alexander Thom surveyed an unusual group of three cairns near Inverness, Scotland, and found significant alignments to the solstice sun on the horizon. The cairns were later carbon dated within a few centuries of 2000 BC. Since Thom significant further work has been published and Thom's astronomical alignments fell out of favour but are now making a (discrete) comeback. The plan below usefully shows artificially raised surfaces which allowed the kerb stones (holding the infill back) to be partially buried rather than set in fully dug holes. The 1997 plan appears to show magnetic rather than true North, 2.2 degrees west of North so I have turned the plan 2.2 degrees anticlockwise.  

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Figure 1 1997 plan of the Balnuaran of Clava with alignments to solar extremes 

These "Clava cairns" have three common concentric boundaries.

  1. an inner chamber that is circular
  2. an outer kerb of standing stones 
  3. a stone circle.

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Figure 2 Chris Bickerton's picture of the Central ring cairn with Southwest passageway cairn behind, and parts of their two rings []

This Early Bronze Age design became a standard type, called the "Clava cairn", and eleven reasonable specimens with passageways have been found. Between the kerb stones and the chamber are boulders below gravel stones, and in most there is a passageway into the chamber. At Balnuaran the northeastern and southwestern cairns have passageways aligned to each other at the angle of midwinter sunset. There is a small stone circle concentric to the cairn. The central cairn's outer circle of standing stones has two stones standing on the winter sunset alignment between the other cairns. Another two of its stones facilitates an alignment to midsummer sunset to the small kerb ring, and another makes the kerb ring the backsight for the midsummer sunrise, beyond the northern cairn.These five stones, surrounding the central cairn, indicate that stone circles, where present around Clava cairns, are like the many stone circles without central cairns, in establishing approximate alignments to key horizon events. Later work indicates alignments to moonrise and moonset at the lunar minimum standstill every 18.818 years, these also having been built into the stone circle of this central cairn. 

The 1997 site plan avoids showing Thom's significant alignments of the two passageways to the midsummer solstice sunset but shows shows three (of the four) raised "causeways" between stones of the central ring cairn's kerb and its stone circle stones, evidently highlighting the midwinter sunset alignment two stones and midsummer sunrise alignment with another.  Recent work by Richard Bradley (Good Stones, 2000), without forgetting solar alignments, noticed the central Cairn had a number of reasons for being located where it is. Building on this, J. Anna Estaroth provides a review and new field work in her Culture and Cosmos paper Clava Cairns, Midsummer Sunset and the Minor Lunar Limit (2017). Richard Bradley concluded the minor moonset in the west was marked by having the central cairn aligned to it from the northern cairn. This prevented the central cairn blocking the light of midwinter sunset down the passage of the northern cairn. This also enabled someone at the northern cairn see the extreme southerly moonset at minimum standstill (as per figure 2), standing beside the central cairn.

It has been noted by Burl and others that the passages of Clava cairns only point to or around the midsummer sunset, alignments associated with the southerly extreme moonsets, at both major and minor standstills and inbetween.

"It has long been known that Clava-type cairns are aligned towards the south-west quadrant (Burl, 1981, 257-65 and Ruggles, 1999, 130, 246, n.78)"  says Henshall and Richie 2001, as you can see from the insert of figure 2, top left, where Clava type cairn passageway alignments are compared.

Estaroth provides extra insights towards the utility of the stone circles around clava cairns, as marking alignments from paired stones in their outer kerbs (Bradley) in addition to their glancing midsummer sunset alignment between the other cairns, etc. Figure 3 integrates past work so as to gain a rich picture of the many solar and minimum moon alignments available within the monument.

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Figure 3 The cumulative alignments to solar and lunar horizon events when the standing stones of the central ring cairn were studied by Bradley and then Estaroth

Balnuaran appears to be the original site for a group of megalithic astronomers whose interests involved the southerly minor moonset. Such an interest is found at Stonehenge and Maes Howe in Orkney, from where Balnuaran's builders might well have come. Anna Estaroth concludes;

The Balnuaran complex exhibits the winter solstice sunset alignment, which might be considered sufficient to explain their purpose. However the ring-cairn’s alignments are with the southern minor moonset and, through the rays, with the northern minor moonrise and set, with equinoctial sunrise, midwinter sunrise and by shadow with midwinter sunset. It would have been lit up by summer solstice sunrise.

This vindicates of Thom's original assertion: that the study of alignments to astronomical horizon events is a required part of interpretating megalithic sites. In contrast, metrology is still not being adopted and any knowledge of historical metrology apparently avoided judging by the lack of its application or of any attempts to record measurements from a megalithic perspective, before sites are disturbed or restored, as with the complete reconstruction of the Gavrinis cairn in Brittany.

...The next article will provide a parallel, metrological interpretation...