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The Modern Antiquarian Forum » Trethevy Quoit » A clean slate? (or should that be granite?) |
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Rhiannon 5291 posts |
May 02, 2011, 18:28
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well if that is the case, that'd be rather cool.
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cerrig 187 posts |
May 02, 2011, 19:00
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Hi stonefree. Can you tell me the date this photo was taken please.
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nigelswift 8112 posts |
May 02, 2011, 19:15
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stonefree wrote: It seems as though the capstone edge is in exactly the right position and has just the right curvature to allow for different elevations of the Sun at different times of year. With respect, that seems most likely to be serendipidy rather than selection or carving and as such can't really be cited as "evidence" in support of what you're claiming. In reply to Rhiannon yes, the midday sun varies in elevation through the year so if you want to know midday each day it would probably be simplest to just scratch a line, like in sundials. Whereas to me, Midday marked by a point (or notch or lightbox arrangement) implies an intention to mark midday on a particular day rather than every day. But I'd go further in my "what's most practical is most likely" musings: I'm thinking a shaft of light shining through a gap wouldn't be my timepiece of choice as if the gap was, say, 5 suns wide, the light shaft doesn't move very well and ought to be much narrower and it would be a real headache to fashion the gap so it worked every day. So shadows are best for marking the time year round - at midday the sun travels about one solar diameter per 2.5 minutes and the shadow reflects that rather sensitively all year round.
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Rhiannon 5291 posts |
May 02, 2011, 20:08
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Well quite. I mean you'd have to look at it every day wouldn't you. And if you just look for something that aligns on the day that you happen to turn up, well next week you might just as well have turned up and spotted something completely different aligning. And then that would suggest coincidence and not deliberateness would it not. can I recommend a four-season sleeping bag.
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drewbhoy 2559 posts |
May 02, 2011, 22:30
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Littlestone wrote: nigelswift wrote: FFS, that's not a clean slate it's a paste of the posting from the old thread, containing sideswipes at people here. Wish I hadn't said it was a bosting idea now. :( Hmmm... I’m beginning to smell socks (again). We have a lot of granite up here in Aberdeen and The Shire, it is wonderful stuff and blocks out the smell of socks. I'm so far away, north of Birmingham somewhere, the smell will never reach my nose. If you can smell it, then it must be close. If I was you I'd go find the offending sock or socks and wash them. Then you could smell the fresh air again. See problem solved!
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stonefree 68 posts |
May 03, 2011, 00:23
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With respect, that seems most likely to be serendipidy rather than selection or carving and as such can't really be cited as "evidence" in support of what you're claiming. It happened - we observed and photographed it and did the maths. Whereas to me, Midday marked by a point (or notch or lightbox arrangement) implies an intention to mark midday on a particular day rather than every day. the important aspect here is not just the notch, but the relationship of the subtly curved capstone edge and the Sun's changing zenith position in relation to it. If this allows the shadow to fall across the notch, at exactly noon, all year round, I would say that is even more evidence of intent! But I'd go further in my "what's most practical is most likely" musings: I'm thinking a shaft of light shining through a gap wouldn't be my timepiece of choice as if the gap was, say, 5 suns wide, the light shaft doesn't move very well and ought to be much narrower and it would be a real headache to fashion the gap so it worked every day. So shadows are best for marking the time year round - at midday the sun travels about one solar diameter per 2.5 minutes and the shadow reflects that rather sensitively all year round.[/quote] Don't forget you have to take into account the angle of the capturing face in relation to that movement, so yes, it would indeed be a real headache (accomplishment?) to position and work the stones so that it worked every day. That's what makes it so amazing - they did, and it still works!
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nigelswift 8112 posts |
May 03, 2011, 03:06
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stonefree wrote: the important aspect here is not just the notch, but the relationship of the subtly curved capstone edge and the Sun's changing zenith position in relation to it. If this allows the shadow to fall across the notch, at exactly noon, all year round, I would say that is even more evidence of intent! stonefree wrote: Don't forget you have to take into account the angle of the capturing face in relation to that movement, so yes, it would indeed be a real headache (accomplishment?) to position and work the stones so that it worked every day. That's what makes it so amazing - they did, and it still works! So two questions arise please: do you see any indication (or have any photos) of whether the subtly curved capstone edge was carved to do so? and have you actually observed (and photographed) the "exactly noon" phenomenon throughout the year?
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Resonox 604 posts |
May 03, 2011, 05:26
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nigelswift wrote: stonefree wrote: It seems as though the capstone edge is in exactly the right position and has just the right curvature to allow for different elevations of the Sun at different times of year. With respect, that seems most likely to be serendipidy rather than selection or carving and as such can't really be cited as "evidence" in support of what you're claiming. In reply to Rhiannon yes, the midday sun varies in elevation through the year so if you want to know midday each day it would probably be simplest to just scratch a line, like in sundials. Whereas to me, Midday marked by a point (or notch or lightbox arrangement) implies an intention to mark midday on a particular day rather than every day. But I'd go further in my "what's most practical is most likely" musings: I'm thinking a shaft of light shining through a gap wouldn't be my timepiece of choice as if the gap was, say, 5 suns wide, the light shaft doesn't move very well and ought to be much narrower and it would be a real headache to fashion the gap so it worked every day. So shadows are best for marking the time year round - at midday the sun travels about one solar diameter per 2.5 minutes and the shadow reflects that rather sensitively all year round. The (reproduction)Steyning sundial...just outside the library, should anyone visit..is a good example of this.
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Resonox 604 posts |
May 03, 2011, 05:38
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stonefree wrote: Resonox wrote: stonefree wrote: We had an expert mathematician calculate from charts at what time the sun would be at it's highest point in the sky at 4.2 degrees west of the Greenwich Meridian. He told us that would happen at 13.19 - and that's exactly what time it was when the shadow fell across the notch! Can I ask...did the mathematician work this out prior to and separately from your timings and the two results compared afterwards or did he give you a time and you worked from this? Also did you film this event...I'd like to see footage of it...not for critique or analysis but just out of curiosity.He's eighty-odd years old and thinks we must be mad because the quoit is probably just a random old pile of rocks! lol I had previously taken photos and the time was recorded in the RAW file metadata. My colleague asked the old man to calculate when the Sun would be at it's zenith for 4.2 degrees west of the meridian but without knowing at what time I had photographed it. We later returned and took another sequence - Result shadow on notch at 13.19 - QED! We're planning on recording video footage in the near future (just waiting for broadcast quality cameras to be delivered!) I can't argue with(or against) cold hard maths...but now can I ask(I know I have so many questions but I find the research fascinating)...is it a given constant that the day you took the photo and the day you returned would have the exact same timings?...I would've thought there would've been a variation depending if you were later(or indeed earlier) in the year. Looking forward to the footage.
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nigelswift 8112 posts |
May 03, 2011, 05:44
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I've played around with home made sundials for years. I think if I wanted to mark midday (or any other time) in a really clear way I'd set up two very narrow, vertical gaps so that a pencil thin line of light would appear at the required time for just 2.5 minutes every day or (if you blocked part of them) at any desired time or day.
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