Astronomy in Da Heights

Foula's North Bank
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.


When he's not tired, fixing his car or caught in train delays, Alun Salt works part-time for the Annals of Botany weblog. His PhD was in ancient science at the University of Leicester, but he doesn't know Richard III.

5 Responses

  1. Very good art­icle on BACAS’s dis­cov­er­ies at Da Heights in Foula. Thank you.

    As you say the mid­sum­mer sun­rise in Foula is at about 40 degrees East of North. That, from Da Heights, it occurs at and moves up the north-west side of Ronas Hill in main­land Shetland is most likely a coincidence.

    BACAS’s work this sum­mer has pro­duced more ques­tions than anwers, but that is the nature of inter­est­ing archaeology!

    Bye John

  2. K Turner says:

    I am a mem­ber of the sur­vey team. The mid­winter sun­rise (140 deg) is the one which we con­sider might be sig­ni­fic­ant. The mid­sum­mer sun­rise was quite spec­tac­u­lar but we are not claim­ing that there is any align­ment of the stone ring in that direction.

  3. J Lawes says:

    I was also a mem­ber of the team and as the pro­fes­sional archae­olo­gist I was con­cerned that what we did was car­ried out to pro­fes­sional stand­ards. The lim­ited excav­a­tion has proved that the circle is man­made, but more than that is hard to estab­lish without fur­ther work and much post excav­a­tion pro­cessing of samples and data. This will take some time, as we are not employed by any body and the work has been done by volun­teers. Dating evid­ence is very dif­fi­cult for a site of this nature and the lack of com­par­at­ive work in Foula makes this even more chal­len­ging. We hope to be able to pub­lish our find­ings within the next year.

  4. Jonathan Harwood says:

    I won­der if the geo­metry of the egg shape has been invest­ig­ated? I refer to Professor Alexander Thom’s (still con­tro­ver­sial and dis­puted) sur­veys of mega­lithic sites (e.g. “Megalithic Sites in Britain” Oxford 1967 & etc).

    I will be vis­it­ing Foula in August. Is the detail of the lay­out vis­ible on the sur­face? Has a detailed sur­vey of the lay­out been done?

    Jonathan Harwood

  5. Alun says:

    There’s some dis­cus­sion of the geo­metry of the site at the Foula Heritage web­site, along with a photo of what you might see.