The earliest astronomers?

Alun Featured, Science, The Past 1 Comment , , , , ,

This post was chosen as an Editor's Selection for ResearchBlogging.orgThe short ver­sion of this post is that Astro­nomy in the Upper Palaeo­lithic? by Hay­den & Vil­len­euve is a great paper. If you’re inter­ested in astro­nomy in hunter-gatherer soci­et­ies you should read it. I’m going to dis­agree with some parts of the paper below, but if Hay­den & Vil­len­euve are wrong about some things, then it’s for inter­est­ing reas­ons. And it’s by no means cer­tain that I’m right to dis­agree about the things that I do.

Reaching for the stars in Lascaux Cave

Reach­ing for the stars in Las­caux Cave. Photo (cc) tourisme_vezere.

The archae­ology of astro­nomy is con­ten­tious at the best of times, but the Palaeo­lithic is a par­tic­u­larly dif­fi­cult period to study, because the remains are so frag­ment­ary and few in num­ber. So to put this in con­text we need to know when the Upper Palaeo­lithic is.

You’re prob­ably famil­iar with the Three Age Sys­tem, Stone, Bronze and Iron Ages. In this sys­tem in Europe the Stone Age ends roughly between 4000 and 2500 BCE depend­ing on where you are and exactly where you want to draw the line. Everything before this is a long time period so you can split it up fur­ther. The Neo­lithic is a period when people settle down and become farm­ers, it starts between 8000 and 4000 BCE in Europe depend­ing on where you are. The south-east of Europe adopts farm­ing much sooner than the people in the north-west. The Palaeo­lithic, if you ignore all sorts of sub­tleties is the period before that. To nar­row down things fur­ther the Palaeo­lithic is sub-divided into three sec­tions, Lower, Middle and Upper. Again, roughly speak­ing, the Lower Palaeo­lithic is the time of early humans, the Middle is the time of Neander­thals roughly 300,000 BCE to 35,000 BCE, and the Upper Palaeo­lithic is the period after that with Homo Sapiens.

This gives the astro­nom­ical read­ers a rough idea of when we’re talk­ing about. Archae­olo­gical read­ers could very eas­ily pick holes in more or less everything I’ve said about the dates. One import­ant reason we’ll get to later is that when we use terms like Bronze Age or Palaeo­lithic, we’re not dir­ectly talk­ing about a spe­cific time, we’re talk­ing about the tech­no­logy we find that’s asso­ci­ated with a spe­cific time. So some ‘peri­ods’ make no sense out­side of Europe. If you live some­where where Obsidian was much easier to get than Bronze, then it’s pos­sible local people never bothered with a Bronze Age.

Hay­den & Vil­len­euve real­ise that evid­ence from the Upper Palaeo­lithic is scant, but they also recog­nise that the Upper Palaeo­lithic is not just a time, but it’s tied to a place. What they’re inter­ested in is whether or not eth­no­graph­ies of mod­ern hunter-gatherer soci­et­ies can give us inform­a­tion about pos­sible uses for astro­nomy. You can’t simply say that mod­ern hunter-gatherers from now were exactly like hunter-gatherers twenty thou­sand years ago, but you can see if tack­ling astro­nom­ical prob­lems pro­duces debris sim­ilar to what archae­olo­gists find. You can also see if there are com­mon fea­tures in astro­nomy around the world from hunter-gatherers. If you can see hunter-gatherer astro­nomy in action then you have clues why hunter-gatherers used astro­nomy in the past and that can pro­duce work a lot more inter­est­ing than “there’s marks on this bone, people could be count­ing moon phases.“
More

Blinded by the Viking Sunstones

Alun Science, The Past 6 Comments , , ,

So, there’s these sun­stones that some people think Vik­ings could have used to nav­ig­ate to Amer­ica. It’s pos­sible though the evid­ence is weak.

A Vik­ing Ship. Not the one you might expect, but wait and see. Photo by Eoghan O’Lionnain

A few months back there was a paper where the phys­ics was sound but the his­tor­ical con­text was lack­ing. Today the news is a new paper, A depol­ar­izer as a pos­sible pre­cise sun­stone for Vik­ing nav­ig­a­tion by polar­ized sky­light. My prob­lem with the earlier paper was that while the phys­ics made sense, there was no real attempt at his­tor­ical con­text. This paper is different.

The test crys­tal from Ropars et al. 2011.

The Alder­ney Stone, from Ropars et al. 2011.

A depol­ar­izer as a pos­sible pre­cise sun­stone for Vik­ing nav­ig­a­tion by polar­ized sky­light is not a paper about Vik­ing nav­ig­a­tion at all. It’s about tests on a sun­stone found on an Eliza­bethan ship by Alder­ney. Update 15 Nov 2001. It’s about tests on a piece of Icelandic spar that the authors have used as a sub­sti­tute for the Alder­ney stone. The paper doesn’t describe the meth­ods used to ensure the sub­sti­tute was a good proxy for the ori­ginal. I’ve included the images of the ori­ginal and the test stone. I can see some super­fi­cial dif­fer­ences and more dis­cus­sion of how the test stone was pre­pared could have been help­ful. The phys­ics is lovely and makes sense, but this paper on Tudor nav­ig­a­tion doesn’t cite any research on Tudor navigation.

The argu­ment is this:

  1. If you place some­thing with a small hole in front of the Alder­ney sun­stone two areas of light appear.
  2. By get­ting the areas to the same bright­ness you can work out where the sun is.
  3. That might have been use­ful in Eliza­bethan times because can­nons can deflect mag­netic compasses.
  4. But we’ve not checked any his­tor­ical records to see how Tudor sail­ors coped with that, nor if our made-up hole thing has any his­tor­ical evid­ence for it
  5. Because sun­stones means Vik­ings! VIKINGS I TELL YOU!

Now, if you’re inter­ested in the optics of cal­cite, this is a good paper — but why would you be inter­ested in the optics of cal­cite? The only obvi­ous reason I can think of is his­tor­ical. And a paper that tackles a his­tor­ical prob­lem by pretty much ignor­ing the his­tor­ical period your arte­fact comes from seems to me to be eccentric.

Any­way, if you were sail­ing in north­ern lat­it­udes and you couldn’t see the sun due to mist, but the light was bright enough for polar­isa­tion to be detect­able, then you could use this device to loc­ate the dir­ec­tion of the sun. The sun­stones would have to be bet­ter polar­isers than the fil­ters I use for my cam­era, because I can’t detect any notice­able polar­isa­tion in the over­cast sky today. Once you have a dir­ec­tion, with no time or alti­tude for the obser­va­tion, what are you going to do with that?

The cov­er­age I’ve seen at the Guard­ian and at the BBC, is cred­ited to two good sci­ence journ­al­ists, yet neither has con­tac­ted a Tudor or Vik­ing his­tor­ian for their opin­ion. This baffles me.

Update 3rd Nov 2011: Wired / Sci­en­ceNow do report that no sun­stone has been found with a Vik­ing ship­wreck or set­tle­ment. They also have an inde­pend­ent expert com­ment­ing on the pos­sib­il­it­ies of Tudor nav­ig­a­tion. Unfor­tu­nately it’s a bio­lo­gist on the dif­fi­culty of sight­ing from a Vik­ing ship.

Is there some­thing clever about the paper I’ve overlooked?

Photo: Vik­ing Line by Eoghan O’Lionnain. Licenced under a Cre­at­ive Com­mons BY-SA licence.