Stonehenge

This work is based on the precise measurements given by Alexander Thom in his paper "Stonehenge" published by the Journal for the History of Astronomy (1974). Thom has also measured other megalithic sites in England and has found a unit of length called "rod"  equal to 2.5 megalithic yards (my) and approximately 6.803 ft.

According to Thom. the main circle of Stonehenge, the sarsen ring, consists of 30 large, upright stones. The inner faces of these stones is flat and polished and their width near the ground is 1 rod. The spaces between them are 1/2 rod, so the inner circcumference is 45 rods (30 x 1.5). The outer faces are rough and most of them rugged, but the mean thickness is 0.48 rods and the circumference 48 rods. These stones were capped by a complete ring of lintels that were cut to the curve of the circle and were all at the same level. Inside this sarsen circle there are three other rings of stones, the Bluestones and the Trilithons. On the outside, there are the Z, the Y and the Aubrey holes. Beyond the Aubrey holes is a ditch that surrounds the monument.

Thom writes that the Z and Y holes are not perfect circles but spirals with radii about 9 to 9.5 rods and 12.5 to 13 rods, respectively. The Aubrey holes have a radius of 141.80 ft and a circumference of 891.0 ft, almost precisely 131 rods. He adds that "if we assume that the intension was to make the circumference exactly 131 rods then we obtain a value for the rod of 6.802 ft which can be compared with the value found in Carnac of 6.803 ft at Le Menec and 6.808 at Kermario". On this circle there are "two so-called stations each of which consisted of a stone in the middle of a mound, the whole being surrounded by a ditch. The rectangle is completed by two station stones; both are still to be seen, one upright and one almost prostrate. There are idications in the underlying chalk that two other stones existed between the Aubrey circle and the bank".

It is obvious that the precise value of the "rod" is not well-known but it is approximately 6.803 ft. If the Aubrey holes have a mean radius of 141.80 ft, the circumference is 890.9557 ft (not 891.0). This means that if it was equal to 131 rods, the rod is equal to 6.8012 ft (not 6.802).

The sarsen ring
If the circumference of this circle is equal to 45 rods, the rod is 8 degrees, the spaces 4 degrees and the radius 45/2π rods. And if the value of the rod - according to Thom - is about 6.803 ft (2.07355 m), then 1 degree is about 0.2591943 m. But (π/2)-1 MC =
0.259173129 m! Thus,


1 rod = 4(π-2) MC = 2.073385 m
                               = 6.80244 ft


We also observe that the arc between the centers of two stones is 1.5 rods, or 6(π-2) ΜC = 3.110077 m
(φ^4 ΜC = 3.11216 m).

I have already mentioned that:

1. The height and the inside width of the Gate of the Lions in Mycenae is 6(π-2) MC (192 d or 3.11 m).
2. The second stone of the second row in the entrance of the Treasury of Atreus (south wall) is 4(π-4) MC (128 d = 1 rod). Also, the height of the first three rows on the same wall is 1 rod.
3. The length of this entrance (south wall) is 10(π-2) MC (319.646 d or 2.5 rods).
4. The width of the four doors in the palace of Tiryns is 4(π-2) MC (1 rod).
5. The diameter of the altar in front of this palace is 4(π-2) MC (1 rod).

The geometry of Stonehenge

(Using a ruler and a pair of compasses only).



Suppose that we draw a circle of radius 1. We inscribe this circle in the square ABCD and we bring the diagonals and the perpendicular lines in the middle. Using the four corners we write quarter circles of radius 2. Thus, we get the rectangle abcd and the points m, s, t and f. This is the basic geometry.

The rectangle abcd is about the same as the one in Stonehenge (formed by the "stations" in the Aubrey holes) and the stylobates of the Parthenon. We observe that the Y holes are inscribed in the quarter circles and the Z holes in the square formed by m, t, and their perpendicular lines on ab. Thus, if the radius of the Aubrey holes KB is 141.80 ft = 20.8437 rods, the radius Km of the Y holes is 12.21 rods and the radius of the Z holes is 8.63 rods. (The difference that exists is small).