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How the Ancients measured the Earth (Megalithic)
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Brian Ambrose



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A sun-dial is the last thing that would work!

Without a clock I suppose he could have set up a system of communication between the two points so that simulaneity could be established, but it's hard to imagine one that would be fast enough. Same applies to the question at hand.

As far as clocks go, why, for example, could Eratosthenes not have had an hourglass calibrated to 24 hours? The same solution would work in Britain (measuring the angle of the sun from the horizon at the moment it appeared in Norfolk).

Sorry Keimpe, I realise I have not addressed your distance problem, but one step at a time...
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Keimpe


In: Leeuwarden, Frisia
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Brian Ambrose wrote:
Without a clock I suppose he could have set up a system of communication between the two points so that simulaneity could be established, but it's hard to imagine one that would be fast enough.


Tuck that one behind your ear for later.
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Keimpe


In: Leeuwarden, Frisia
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Brian Ambrose wrote:
A sun-dial is the last thing that would work!


Alright, how about a simple stick then?

I got this from elsewhere:

Mark out a line on the ground that runs north to south.
To determine when it's noon (without a watch or radio) place a stick at the southernmost end of your north-south line. Use a plumb line to make sure that the stick is vertical. When the shadow cast by the stick crosses the north-south line, it's noon.


Of course, this is perhaps fifteen minutes off to either side of noon, but it's still a valid method to determine noon without a watch, especially for those who haven't got one.
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Brian Ambrose



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Keimpe, you cannot use the sun to determine simultaneity at two geographically different points - both points (of the orientation we're discussing) will believe it's midday whereas we know (and rely on for the measurement we're trying to make) that they can't both be at the same time.
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Keimpe


In: Leeuwarden, Frisia
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Brian Ambrose wrote:
Keimpe, you cannot use the sun to determine simultaneity at two geographically different points - both points (of the orientation we're discussing) will believe it's midday whereas we know (and rely on for the measurement we're trying to make) that they can't both be at the same time.


You're right if you are thinking of both ends of the St. Michael Line, but I was thinking about the Egyptian situation: two points directly North-South of each other. They both have noon at the same moment (this is what time zones are all about).

So let's move on agreeing that it's pretty hard to share one same moment at both ends of the St. Michaels Line (because they are not north-south oriented), and proceed with the measurement question.
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Brian Ambrose



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They both have noon at the same moment


But how do you know when 'at the same moment' is? Do you have a relay of shouters going, "oi, it's twelve o'clock" (very slow)? Or a series of fires on hills (slow)? Maybe a cunning series of mirrors (hard to engineer)?

Unless we're saying 'at the same moment' is when each shadow is at its shortest. But that then changes the question to, how is the not-the-shortest shadow stick ever calibrated?

So let's move on agreeing that it's pretty hard to share one same moment at both ends of the St. Michaels Line (because they are not north-south oriented), and proceed with the measurement question.


hard...to...move...on. When we haven't established how E synchronized Aswan and Alexandria.

Is it that hard to systematically measure the distance using standard surveying techniques? (for hills, theodolites and trig).
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Keimpe


In: Leeuwarden, Frisia
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Brian Ambrose wrote:
Unless we're saying 'at the same moment' is when each shadow is at its shortest. But that then changes the question to, how is the not-the-shortest shadow stick ever calibrated?

It's not about the length of the stick, it's about the fact that the sun comes up in the east and sets in the west, whilst moving through the southern skies. Halfway through the day (which we call noon) it crosses the North-South line. So if you draw a one yard line with your foot (directly north-south), and put a vertical stick in the ground at the southern end, the shadow will 'disappear' behind the stick at noon.

Now, if you have two locations that are North South of each other (like (roughly) Amsterdam and Johannesburg), they both have noon at exactly the same moment, whether you use the watch or the stick.

hard...to...move...on. When we haven't established how E synchronized Aswan and Alexandria.

We're not interested in E. He's just the most famous person that ever actually tried to measure the earth. But he did everything wrong, so it's a waste of time to try to recreate his measurement, while we're looking for a better one.

Is it that hard to systematically measure the distance using standard surveying techniques? (for hills, theodolites and trig).

I'd very much like to know how to measure the distance between two hills and whether this could have been done several thousand years ago. Could you tell me more on this? It may make my final solution even more simple.
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Brian Ambrose



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It's not about the length of the stick

Yeah, I know. It's about angle of the stick relative to its base, and that's what I'm talking about calibrating. I am assuming that the final calibration of the stick would be done using the sun itself (especially if you're using a well), although using a spirit level would provide a good starting point.

We're not interested in E. He's just the most famous person that ever actually tried to measure the earth. But he did everything wrong

Maybe he did, but he did it better than us so far, so it's worth seeing what we can learn from him.

I'd very much like to know how to measure the distance between two hills and whether this could have been done several thousand years ago.

Well, I'm not saying you can directly measure the distance between two hills, but you can measure the distance down to the bottom of the valley between, and using the angle of the hill work out the direct line distance. But you're looking for a more accurate method.
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Keimpe


In: Leeuwarden, Frisia
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Brian Ambrose wrote:
I am assuming that the final calibration of the stick would be done using the sun itself

Since we're interested in a north-south direction, I'd use the pole star for calibration.

he did it better than us so far, so it's worth seeing what we can learn from him.

Au contraire Brian. Had Eratosthenes been able to read some of your remarks, he would have hit himself over the head with a hammer, for not thinking of it himself.

you can measure the distance down to the bottom of the valley between, and using the angle of the hill work out the direct line distance. But you're looking for a more accurate method.

No, no, I was just curious if there was a simple method to measure distance between two hills. Let it rest, please, we're getting too many sidesteps here.
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Chad


In: Ramsbottom
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Keimpe wrote:
What we need is a part of England that is relatively void of hills. Any suggestions? I know of one...


Salisbury Plain?
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Keimpe


In: Leeuwarden, Frisia
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Chad wrote:
Keimpe wrote:
What we need is a part of England that is relatively void of hills. Any suggestions? I know of one...


Salisbury Plain?


I don't know how big it is, but I think it's too small.

There's one more prerequisite though, that disqualifies Salisbury Plain: it's not attached to the St. Michaels Line. We know sun rises over the St. Michaels Line May 1st, so now we're looking for an adjacent plain(ish landscape). After all, we want to measure the distance from A to B where clearly the St. Michaels Line is the start or the finish. Does any other region come to mind?
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Hatty
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In: Berkshire
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Very flat in Norfolk. I don't want to muddy the water but does the meridian line have any bearing on this?
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Hatty
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Since we're interested in a north-south direction, I'd use the pole star for calibration.

Does the Gamma Draco star have any significance? This is apparently what Hooke was looking at from his 'well' (Monument). I read somewhere that c 4,000 years ago it was aligned to Avebury (not clear how this fact was deduced) so presumably Silbury was the equivalent of Greenwich observatory.
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Keimpe


In: Leeuwarden, Frisia
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Hatty wrote:
Very flat in Norfolk.

Indeed it is. But I'm afraid there's not enough room for our experiment. You see, we're not looking for a way to extend the St. Michaels Line across the globe, because even though that would give us a circumference, it would be a meaningless one.

What we need is the Polar circumference, because that's valid everywhere on earth.

And therefore we have to have a flat(tish) part of England in a north-south direction that extends for perhaps some 100 km (1 degree of latitude) to get a decent measurement.

I don't want to muddy the water but does the meridian line have any bearing on this?

In what way?
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Keimpe


In: Leeuwarden, Frisia
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Hatty wrote:
Does the Gamma Draco star have any significance? This is apparently what Hooke was looking at from his 'well' (Monument). I read somewhere that c 4,000 years ago it was aligned to Avebury (not clear how this fact was deduced) so presumably Silbury was the equivalent of Greenwich observatory.

Do you have more information on this? Perhaps a link I can follow? I'd like to know more.

Hatty wrote:
so presumably Silbury was the equivalent of Greenwich observatory.

Ah, was that why you were talking about meridians?

Silbury is indeed crucial in this story - wink, wink, nudge, nudge.
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