Astronomy in Da Heights

Foula’s North Bank. Photo (cc) C41lum.

An interesting story came out recently in the Scotsman. A survey of archaeological sites on Foula in the Shetland Islands has revealed what looks like a stone circle with an alignment pointing to the midwinter sunrise. The circle was found at Da Heights on the north of the island and it’s been confirmed with geophysical survey and limited excavation. If you’re wondering how you could get a circle to point anywhere, then I should add this circle is egg-shaped. It’s interesting because the archaeological survey is almost certainly sound, but proving the significance of the alignment is another matter.

The reason I’m happy to accept the findings of the survey is that the Bath and Camerton Archaeological Society, who conducted the survey, have put up information about what they’re doing on the web. You can also read about the survey at Foula Heritage. From reading these pages it’s clear they’ve found an interesting site.

Where I get more wary is in the astronomical claims for the site. In the Scotsman story there’s a quote:

“It turns out that the winter sunrise goes right up the middle, while the summer solstice rises at right angles to it.”

If you look at the plans the circle appears to point to an azimuth of 140°. This is a long way south, in fact 50° south of due East. This is due to the island’s northerly location, the further north you are from the equator the more southerly the midwinter sunrise and sunset. Equally the further north you are, so too the midsummer sunrise and sunset move north. If the midwinter sunrise is 50° south of East, then the midsummer sunrise – given a flat horizon should be around 50° north of East. The sea is to the north, so I’d expect the midsummer sunrise to be at an azimuth 40°. That’s a difference of 100°. It could be that the accuracy doesn’t matter – in which case the claim is true but it’s trivial. It’s almost impossible to build anywhere in the British Isles where that kind of geometry wouldn’t exist.

All that’s certain is that the circle has one alignment and an egg-shaped circle is bound to point somewhere. You could also argue for astronomical significance if it pointed to midwinter sunset or midsummer sunrise/sunset. If the circle pointed to one of the cardinal points that could also be significant. There’s also evidence of lunar alignments in some prehistoric sites in Scotland, which gives you eight further targets for lunar standstills. If you say any given site is aligned +/1° then the odds of randomly aligned sites pointing to something significant is less than one in eight. This doesn’t mean that the circle’s alignment is not significant, simply that proving it becomes difficult.

One way to do that would be to compare it with any other similar local sites of the same period. Unfortunately Foula’s small, around 5km by 4km, so there won’t be a large sample to compare it with on the island. It could be compared with sites on the other Shetland Isles, it’s only around 25km from the mainland so interaction would have happened. I don’t know much about Shetland’s archaeology, so I can’t recall if there’s anything similar.

Further away on the Orkney Isles, there certainly are other comparable sites, like Maes Howe which is also aligned to the midwinter sunrise, which would seem to bolster the claim that the alignment at Foula is significant. There are some differences between Shetland’s and Orkney’s archaeological remains, so I don’t know how far the comparison would be reasonable.

A problem with relying on regional surveys though is that each archaeological site is local, not regional. Even if there are regional cultural processes which were operating on prehistoric Foula, they would have acted in the very specific circumstances of Foula’s own landscape. If there are distinctive regional patterns then some of those sites must have been intentionally orientated, but it seems impossible to be certain about which specific sites show this intention.

Given the context of the site in the northernmost part of the British Isles I don’t agree the midsummer alignment argument. In contrast I do think the claim that the midwinter alignment was intentional is eminently reasonable. The combination of landscape study as well as excavation suggests it will be a fascinating report to read once it is finished.