Re: A clean slate? (or should that be granite?) | Forum

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Rhiannon May 2, 2011 20:08:44

Replying to nigelswift

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.

S

stonefree May 3, 2011 00:23:05

Replying to nigelswift

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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Resonox May 3, 2011 05:26:20

Replying to nigelswift

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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stonefree May 5, 2011 20:40:28

Replying to nigelswift

The rather clever thing about having a 3 dimensional 'hole' with a varigated diameter profile as well as a non-linear depth, is that it becomes possible to work out very accurate positions using the extinction angle whereby you can no longer see the Sun through it. Once you have this capability, all you need is an equally accurate time marker and you can then work on producing an analemmic curve of the sun's apparent path and therefore work out that the planet is kind of spherical and wobbles as it spins. The combination of the capstone aperture and noon notch may have enabled such observations!