Portal tomb observation problems . | Forum

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theCaptain May 3, 2011 09:41:37

Replying to tiompan

Just a small point, but one I think would be of major significance. Over the thousands of years these stones have been in place, I am pretty sure that they will have settled and moved by significant amounts, in some cases by large amounts.

Has any account been made for this? I don't see any mention of it anywhere - but I am not looking in detail.

I mentioned this elsewhere, but it seems to be ignored.

H

Horsedrawn May 3, 2011 09:45:16

Replying to tiompan

These considerations are vital, of course, and thank you, but please do not assume they have not been taken into account. They have; and more.
Of necessity, the present study is of how the structure works now. The differences that exist due to its longevity have to be worked out theoretically, and over the last ten years a lot has been done. I do try to leave nothing out, and more penetrating questions like yours are very welcome indeed.

David Kane.

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tiompan May 6, 2011 07:51:38

Replying to tiompan

tiompan wrote:

We have 23 RC dates from Portal Tombs ,all are termini ante quos and clearly cannot date the build .The best example of a date associated with build is Sperris , where the deposit was overlain by the doorstone .The results show that the first Portal tombs were built around 400-3800 BC and no later than 3600 BC .The dates from the deposits at two PT’s not far from Trethevy , Sperris and Zennor were 3633-3557 BC and 3342 -3024 BC . It is not unreasonable to assume that Trethevy was built around the same period i.e 3024 -3633 BC .It does not need an expert anything to calculate the the azimuth and altitude of the sun at any given date but it is worth pointing out to those that are doing observations in the 21st C that the azimuth and altitude at a certain time of day on a particular date this century would differ from that around 3024 BC . Depending on the month the azimuth could differ by 7 degrees which is the case at summer solstice or a difference of 6 degrees altitude in November .If these changes are not incorporated into calculations regarding light and shadow phenomena found at monuments like portal tombs then what is seen today is not the same as what would be seen at the same time and date when they were built .
It is not a major problem for these particular measurements but when recording data like longtitude , it is worthwhile getting it right , making mistakes when you go to bother of noting decimal point(s) does not inspire confidence . The longtitude for Trethevy is 4.55 not 4.2 as mentioned elsewhere .

Wild speculation is one thing but when speculators stray into areas where we have real data then the cracks and ignorance are more obvious . There has been a suggestion that Trethevy may be older than Newgrange by 1000 or 1500 years . It might be younger too but what we do know is that the RC dates for Newgrange suggest a build date around 3200BC .The oldest likely build dates from any portal tomb are from Carreg Coetan 3778-3376 and Poulnabrone 4050-3697 and it is suggested that the earliest date is likely to be no earlier than 3930 . The Cornish PT's as mentioned above are later with Zennor being 3342-3024 .Whichever way you look at these figures the 1000 -1500 year earlier than Newgrange seems typically imaginative and it appears they may have been pretty close to being contemporary . Of course if Trethevy was as old as they suggested the astronomical calculations would be even further "out" as I gave them them benefit of the doubt by using the later dates .1500 years added to the Newgrange date takes us 4700 BC there are no megalithic monuments that we know of in the UK at that date .