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Alexander Thom L1 / 7 Class III Survey

Construction: Type B flattened circle (Li/7). Diameter 359 ft = 131.9 my. Perimeter 390.0 my = 156.0 mr. The flow of the earth down the slope may have displaced the stones, leaving the more deeply set stones slightly behind. Long Meg as seen from the construction centre indicates the setting midwinter Sun and seen from the same centre the stones at Little Meg (Li/8) indicate the Sun rising at May Day/Lammas.

Long Meg

Alexander Thom Site Plan from BAR
see photos and site visits at http://www.megalithic.co.uk/article.php?sid=101

Aubrey Burl (Cumberland 23)

This is one of the largest British rings. It is in State care. It was built on a slope at 100 m O.D., 2 1/4 miles N of Langwathby. It is about 359 x 305 ft (109 x 93 m) in diameter.

Some 70 local porphyritic stones remain of a ring flattened at the N. 2 massive blocks stand at the E and W of the circumference. There are traces of a bank at the SW. 2 large stones at the SW define an entrance. 25 m beyond this is Long Meg* a red sandstone pillar possibly brought from the Eden valley i| miles away. Its SE face has several carvings of rings and spirals on it.

John Aubrey reported that 2 large cairns stood at the centre of the ring. William Stukeley noticed remains in 1725 but they have now gone.

There is a tradition that the ring has been disturbed and rebuilt.


W. Stukeley. Itinerarium Curiosum II, 1776, 47. J. Y. Simpson. Archaic Sculpturings..., 1867, 19-21. C. W. Dymond, TCWAAS 5, 1881, 39. T. Clare, TCWAAS 75, 1975, 7.

J. Aubrey. 'Monumenta Britannica1, 1670-97, c. 24, 72-3.

Previous Article

One of the key objections for the megalithic building flattened circles concerned their use of ropes and a knowledge of geometry in managing radii to achieve a lesser circumference than a circle would have. If instead Thom's Type A or Type B flattened circles were constructed using a grid of squares, then some of the all-important key points where a flattened circle's radius of curvature changes (of which there are only four) should be points of intersection within the grid intersections. It became clear that this was a possible alternative means to their production when considering the Type A geometry and specifically its implicit pair of triple-square triangles, as right triangles available within such a grid.

Robin Heath has already noted [in Sun Moon and Earth, p52-55] that these triangles are close to the invariant ratio, in their longest sides, of

  1. the eclipse year and solar year, and
  2. this same ratio is also to be found between the solar year and the thirteen lunar month year.

The baseline of such a right triangle is found to be 6/7 of the diameter MN of the Type A flattened circle and this implies, given the left-right symmetry of this form, that the key point at the end of the hypotenuse (where the radius of curvature changes) would sit on the corner of a grid point of 14 by 14 squares, as a length then equal to twelve grid units. The forming circle used by Thom, of diameter MN, would then inscribe the grid square. 

GRID 28x28 NoRigg

Figure 1 Type A drawn on a 14 square grid

We also know, from Carnac, that the astronomers used a triple square to frame this right triangle so as to relate the periods of eclipse and solar year. Since the vertical position of the key point is 12 units, then to left and right the key points either end of the central flattened arc are 4 units, either side of the central axis. Therefore, to right and left of these triple squares can be found two four-square rectangles, whose diagonals express (with an accuracy better than a day count could could) the relationship of the lunar year (side length = 4) to the solar year (as hypotenuse/diagonal). These four squares (each 3 by 3 = 9 grid squares) have a baseline of twelve grid squares which exactly matches the number of lunar months within the lunar year.

One therefore sees useful megalithic  "resources" within such a 14-square grid in that many multiple squares can be formed; such as these triple squares either side of the vertical centreline have two four-square rectangles to the right and left (shown in red below, the ripple-squares being blue). These leave a row of 14 by 2 squares at the top which can be seen as a seven-square, the rectangle whose diagonal to side alignment is found between a double and a triple square: These include triple and four square rectangles which give good approximations in their ratios, between diagonals and longer side lengths, which can be used as calendric devices for lunar to solar year, eclipse to solar year and solar to 13 month year.***

***This habit, around megalithic Carnac, of "finding" right triangles within multiple squares corresponds to the astronomical reality whilst enabling accurate generation of these counted lengths without any day counting of periods; once the triple square and four square were discovered to be "cosmograms"

The other two points at which a Type A's radius of curvature changes, lies a further two grid squares from the central axis, but falls exactly half way; along the vertical edge of a grid square. To achieve a grid in which these two key points would also be commensurate, the number of squares in the grid needs to be doubled to 28, or so it would seem. But in practice the metrology of a grid's side lengths would have ready made subdivisions, especially by half, and so one comes to the question of how early metrology defined units of length. 

GRID 28x28 NoRiggUses

Figure 2 Some of the multiple squares present within the grid.


NEXT: Thom's Stone Circle Geometries: 3. Tracking the Sidereal Day 


First Article | Previous Article >

In previous artices in this series it has been shown how disingenuous criticism of Alexander Thom's flattened circle geometries were, and how this has prevented further progress in understanding how they could have been (a) constructed, without ropes by using a grid, and (b) how the type-A for example can be organised using the multiple square geometries of megalithic Brittany (4700-3000BC). The location of useful astronomical geometries within a flattened circle, once drawn using squares rather than ropes, implies that flattened circles could have been a standard useful design for calculating and tracking important time periods. This idea can be taken further into the domain of observational astronomy, if such circles allowed observers to know which parts of the ecliptic are rising and setting on the horizon. In this regard, the circumpolar stars offer a natural timepiece rotating in the north, of a clear pattern of distinct stars and constellations: a design which is also circular.

In Sacred Number and the Lords of Time, I propose that circumpolar astronomy was practiced in the megalithic, from Brittany onwards, and this can account for the northerly alignments found within monuments, as being used to track sidereal time through either (a) direct viewing of the circumpolar region or (b) by noting the azimuth on the northern horizon of key (marker) stars which never set. The naked eye astronomer can then watch the circumpolar region and know the sidereal time through a direct experience even though there are distortions due to the angle of the ecliptic relative to the celestial equator, the ecliptic being skew to the polar axis and the circumpolar region being somewhat distorted by the act of reducing stars to their azimuth on the horizon.

With this in mind, another megalithic use for the Type A flattened circle can be imagined once one observes when the winter solstice point (on the eclipic) rises on the eastern horizon and when the summer solstice points rises, the time between is eight hours (in southern Brittany, 4300 BC). It then takes sixteen hours for the winter solstice point to again rise on the easter horizon. This observation can be done on winter solstice sunrise so that the sun will be setting eight hours later. Observations after summer solstice sunrise will offer a time (at Carnac) of sixteen hours. The generalisation that the length of the shortest winter day or longest summer day at a given latitude could tell the megalithic astronomer how to calibrate the circumpolar disc. In north-west Europe though, the days division of light and dark at the extremes of the year was very simple and the megalithic observer found the duration of the dark period (night) for one solstice equals the duration of the light period (day) for the opposite solstice. At latitudes near southern Brittany one also finds that the lesser period is 8 hours long and the longer period 16 hours as below.

GRID 28x28 NoRigg SiderealDay web500

The sun rises with the extreme northerly tip of the ecliptic at summer solstice and takes 16 hours before setting, at which point the most southerly tip of the ecliptic is rising on the horizon, and a night of 8 hours begins before the sun again appears still sitting near the northern extreme of the ecliptic. The Autumn equinoctal point, where the ecliptic drops below the celestial equator, rises at the midpoint between the solstitial points, and eight hours of earth rotation from each. The Spring equinoctal point sits similarly between the solstitial points, and four hours after the winter solstice point and four hours before the summer solstice point. This time sequence is forever slowly changing due to the progress of the sun along the equinox in (above) an anti-clockwise cycle through the year, with about 365 steps between positions at sunrise. This manes that any counting regime, of days around a circle representing a solar year, is naturally congruent to such a circumpolar understanding.

One can look at the circumpolar sky using software to see the actual pattern of stars that would have greeted the astronomers 6000 years ago, Firstly, one can see the circumpolar stars at summer solstice sunrise (or by symmetry, at winter solstice sunset):

Brittany Circumpolar 2oclockimage made using CyberSky

One is struck by the obvious fact that the Big Dipper is behaving like an hour hand for what we call the "two o'clock" angle of a modern clock's hour hand. In fact, the big dipper appears carved as a pattern of dots in the door jamb of La Table des Marchants, with an implied geometry of the 3-4-5 triangle, whose smaller angle defined the azimuth of solstices relative to east-west (sunrise or sunset).

MarchandsQuestionMark Interpretation 2

If the midsummer sunset is observed in the northern sky at this epoch one sees the distinctive "question mark" down at the six o'clock position:

Brittany Circumpolar 6oclock

image made using CyberSky

The megalithic observer would therefore conceptualis the rotating pattern of stars according to the picture below, shown in the six o'clock position.

Brittany Circumpolar combined

By looking at this timepiece, the parts of the ecliptic that were rising or setting on the horizon could be known, with particular focus on the four "gates" of the solar year, the solsticial and equinoctal points, in a pattern deduced from noting the dark periods of the two solstice days as in the ratio one third (summer) and two thirds (winter) of a complete (sidereal) day of one earth rotation. This same circle is the year circle of 365 days, reducing astronomy to a design naturally visible at the circumpolar region and which is elegantly presented in the Type-A flattened circle, a circle based upon the division into one third and two thirds.

NEXT: Thom's Stone Circle Geometries: 4. Role of Metrology within Type A