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Keimpe
In: Leeuwarden, Frisia
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What happens now?
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Hatty
Site Admin
In: Berkshire
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This and any other megalithic topic can be discussed on the Megalithic Empire discussion forum from 15th September on.
I've asked Dan's permission to put his Appendix on How The Ancients Measured The Earth on the new site.
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Hatty
Site Admin
In: Berkshire
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| Keimpe wrote: | | Mick Harper wrote: | | As to finding it again [.....] they built three towns on the Welsh side of the Bristol Channel with identical names to three towns on the English side, each pair being equidistant from the latitude of Lundy Island. |
That's an amazing find (is it yours?). Although to me these six towns don't look like aids in finding Lundy. It's more like "now look, professor, how much more of this need I show you before you stop telling everyone it's all a coincidence?" |
The definitive book on prehistoric geometry, Seeing Around Corners: Geometry in Stone Age Britain -- The Proof, by Tom Brooks has uncovered the network for all to see. The reviewer Geoff Ward writes at length about Tom's work http://www.mysteriousplanet.net/earth-mysteries.php and has this interesting snippet:
| Key features of the network, which Tom regards as chiefly navigational, are the equidistant spacing of aligned sites either side of a third, as with Silbury Hill and a standing stone on Lundy Island, off the coast of Devon (never previously uncovered), and at the Stoney Littleton long barrow in north-east Somerset (see item at the foot of this page), the significance of which, as a major locus, is a dramatic new finding. | |
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Keimpe
In: Leeuwarden, Frisia
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I've ordered it. Looks very, very interesting!
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Hatty
Site Admin
In: Berkshire
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I'd very much like to hear whether you think we should read it. I hesitate to ask because last time you recommended books (by Knight and Butler) they blew my mind away. All in the line of duty.
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Boreades
In: finity and beyond
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Boreades
In: finity and beyond
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It's a dead link, Jim!
| Keimpe wrote: | | Now, all I needed to 'prove' the ancients could measure the earth, was prerequisite B: another location some 50 to 100 kilometers away (preferrably straight to the north) where the angle towards the sun would be measured at the exact same moment. But where on earth could that second location possibly be?? Is there a second Silbury-Waden-Hill-like aligment on May 1st somewhere? Any ideas anyone? |
Getting warmer.
You've all been getting so warm I can see the scorch marks!
At least, I've assumed that's what the brown stains are.
The Michael Line is irrelevant to this topic. So are any other diagonals. Bonfires and mirrors are irrelevant as well (unless we're talking lighthouses and beaconages). Hatty was closest with the Pole Star ( in spite of Mick's sarky note that she has no sense of direction - allegedly)
| Ishmael wrote: | | I have read a book called "It's All Done with Mirrors" in which the author (I forget but Mick knows him) argues that the British Foot was the basis for all other distance measuring systems the world over. |
"All Done with Mirrors" is by John Neal. He makes some very valuable contributions to our understanding of ancient metrology.
e.g.
The Earth is not a true sphere, but is subject to polar flattening, which means that the longitudinal meridian, or the great circle through the poles, is essentially elliptical. The distortion is minute, but it creates a measurable variation from degree to degree. Degrees nearer the poles are longer than those at the Equator. Thus, a widely accepted value for the Greek Foot of 1.0114612 British Foot proves to be 1/360,000th part of the longitudinal meridian degree at just under 38° latitude - the same latitude as that of the Aegean. There was therefore a practical reason underlying variations between the ancient Foot standards that need not be put down to carelessness or error.
| Mick Harper wrote: | | If anybody wishes to put together a piece showing how, in practice, megalith-makers measured the earth's circumference, they are guaranteed publication. |
Ooohh! Me Sir, me! It might be that the Greeks learnt how to measure the Earth's circumference from British or Gaulish Druids, using stars instead of the Sun.
Posidonius (for example) is a fascinating character, acclaimed as the greatest polymath of his age. Reportedly he had travelled as far as Gaul and knew of the Druids. Posidonius later calculated the Earth's circumference by reference to the position of the star Canopus. As explained by Cleomedes, Posidonius observed Canopus on but never above the horizon at Rhodes, while at Alexandria he saw it ascend as far as 7 degrees above the horizon (the meridian arc between the latitude of the two locales is actually 5 degrees 14 minutes). Since he thought Rhodes was 5,000 stadia due north of Alexandria, and the difference in the star's elevation indicated the distance between the two locales was 1/48th of the circle, he multiplied 5,000 by 48 to arrive at a figure of 240,000 stadia for the circumference of the earth.
According to http://en.wikipedia.org/wiki/Posidonius
A different method to Eratosthenes.
Due north is my emphasis. Rhodes might not be truly north of Alexandria, and the distance might not be exactly 5000 stadia. But the principle is the same and the formula is the same.
As Keimpe has already pointed out, the good reason folks measure along a meridian is so that they are always in exactly the same time zone, so there is no need for clocks to record or allow of the time, and any differences in astronomical measurements made from two positions on a meridian are only because of the difference in latitude (E&OE)
| Hatty wrote: | | I've asked Dan's permission to put his Appendix on How The Ancients Measured The Earth on the (TME) site. |
What? Where?
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Hatty
Site Admin
In: Berkshire
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Boreades
In: finity and beyond
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Depending on who you ask, a Stadia might be about 185 meters. So in kilometres, Posidonius' meridian baseline was 5000 x 0.185 = 925 Km or 578 miles.
Does it have to be so long? No, but the longer you can make it, the greater the difference in maximum ascension of the star at the two measuring points, and that minimises the effects of the margin of error of the measurements made by hand and eye. For an anology, think of a one-foot ruler, and using that to measure (a) the width of a page of A4 paper and (b) the thickness of 10 sheets of paper. Which would you say is the most accurate?
By way of comparison, where might a suitable meridan be in Britain?
A hypothetical meridan north from Silbury reaches the Shetlands after 997 Km or 619 miles.
A hypothetical meridan south from Scara Brae reaches Budleigh Salterton 938 Km or 583 miles.
But (it seems to me) there might be a problem with these meridians. How would you measure the length of the meridan when it crosses water? Not easy, unless our megalithic surveyors also knew about measurement by triangulation? But to do that, you still need to start with a datum, or baseline, that is onland and accurately measured.
So, we're back to Keimpe's original question!
Where's there a suitable meridian in Britain?
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Boreades
In: finity and beyond
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To protect our sanity, we're not aimlessly thrashing around looking for any old megalithic sites on a meridan. As candidate astronomical observatories, we're looking for places with certain key features.
- an unnaturally level or engineered site
- clear site lines over a horizon at exactly the same height
- evidence of very careful site preparation e.g. a clay floor.
As observed by Hatty, Silbury certainly ticks the first two boxes.
Why would you need a clay floor? Clay does have a few special properties as a building material, it's soft, easily shaped, can be rolled thin yet still be impervious to water. Like a pond liner. Especially useful if you want your henge to be filled with water that doesn't just drain away. But why would you want to do that?
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Boreades
In: finity and beyond
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| Hatty wrote: | | Dan's How The Ancients Measured The Earth can be downloaded from the menu on the left here http://www.themegalithicempire.com/forum/ as a Word doc. As always with Dan's articles, it's well worth reading. |
That's fine, we just need to replace the section on Eratosthenes with Posidonius. And forget about sticks and shadows, and lighting bonfires. It's an astronomical measurement, not solar.
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Tilo Rebar
In: Sussex
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| Boreades wrote: | | ...It's an astronomical measurement, not solar. |
As today is the very day when the sun sets exactly due east at exactly the same time all the way along the N/S meridian, this could be the right occasion to use the sun as a timing signal for measuring the circumference of the Earth. This solar signal could be used to time two measurements of the angle between a precisely level horizontal surface on Earth and of a celestial body. This being done from two locations at a large distance away from each other on the N/S meridian.
There may be a snag with this conjecture, however, as few distant celestial object are easily visible during the early evening, with the exception of this...
Identifying pairs of possible locations which could have been used should be fun.
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Boreades
In: finity and beyond
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Avebury ticks the boxes for another very special reason. Whereas Stonehenge is significant for solar reasons, Avebury is astronomically aligned. Avebury is also one of the ancient temples of the world positioned on exact longitudinal fractions.
Giza is 1/3rd (30 degrees) of the quadrant (equator to pole)
Thebes is 2/7ths (25.7 deg)
Avebury is 4/7ths (51.42 deg) or 360/7
360/7 is 51.42857142857143
Put that in a geosite as the longitude and what do you get?
e.g.: http://www.findlatitudeandlongitude.com/?lat=51.42857142857143&lon=-1.8538&zoom=16
Usually with our attempts at alignments and meridians, places are fairly close, or quite close, or close enough. Avebury , however, is none of these. It is absolutely spot-on, to an astonishing degree of precision.
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Mick Harper
Site Admin
In: London
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I am confused. You have posted up a pic of Avebury which is some distance from Silbury.
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Boreades
In: finity and beyond
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You must be seeing things. ;-)
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