Woodhenge: the line and the rings

Abstract. The claimed solstitial alignment of Woodhenge is not supported by the layout of its posts. It rests on a line drawn on Cunnington's 1929 plan at the midsummer sunrise bearing (49.4° true, the first gleam in 2500 BC). When the 156 marker posts are fitted ring by ring, every long axis lies north of that bearing. The outer rings A and B are 10–12° north of it, and their 95% ranges exclude the sunrise. The inner rings C–F are 4–8° north. They are too loosely defined to rule the sunrise out, but they do not demonstrate it. Along Cunnington's line from the centre, the view passes through ordinary gaps between posts, and the gaps themselves are centred a few degrees further north.

The June post on Woodhenge accepted the textbook position: the long axis of the timber rings points, broadly, at midsummer sunrise. That position rests on one line, the dashed axis on Maud Cunnington's 1929 plan, labelled "line of midsummer sunrise, elevation of horizon 30′". The new Woodhenge 3D model allows that line to be tested against the post positions themselves. The result is that the line meets the sunrise, but the rings do not follow the line.

The model and its checks

The model places the 156 ring posts (A 60, B 32, C 16, D 18, E 18, F 12) on the concrete markers set out by the Cunningtons, in Ordnance Survey coordinates, on lidar-derived terrain. The twelve supernumerary holes are not included. Two independent plans were used to check the geometry:

• Cunnington's 1929 plan, with its postholes detected automatically and matched to the model by a scale-and-rotation fit: median residual 0.24 m (90% within 0.48 m), rotation −0.1°, no measurable stretch.
• The 2008 GPS survey of the markers by the Jenks brothers: median residual 0.06 m, rotation 0.0°. Three ring-A markers in the east-south-east are missing from that sheet but present on Cunnington's plan.

The centre of the post pattern lies within 1 m of the published position of the monument. The markers are an interpretation of the holes rather than the holes themselves, and they do not precisely preserve the excavated positions (The Past, 2025), but the fit to Cunnington's own plan shows that any such error is well below a metre.

The sun

Sunrise and sunset are computed with the astronomy-engine library (apparent positions, standard refraction, solar semi-diameter 0.27°) against a skyline measured from the lidar terrain at an eye height of 1.6 m above the centre. In the solstice direction that skyline stands at 0.45–0.51°, in good agreement with Cunnington's 30′. For 2500 BC the most northerly midsummer sunrise falls at the following true azimuths:

• first gleam: 49.4°
• half disc: 49.8°
• full disc on the horizon: 50.2°

The modern equivalent (first gleam) is 50.1°. Midwinter sunset in 2500 BC falls at 229.7–230.6°, over a skyline of 0.28°. On this terrain the south-western horizon is lower than the north-eastern one; any obstruction of the midwinter sunset would have to come from something not in a bare-earth model, such as vegetation.

Cunnington's line

Registered to the markers, Cunnington's dashed line lies at 49.4° true and passes within 0.3 m of the centre of the post pattern. It therefore points at the first gleam of the 2500 BC midsummer sunrise to within a tenth of a degree. On the plan the line is marked 50¾° from her north arrow. When the plan is registered, that arrow sits about 1.3° west of true north, which accounts for the difference between the label and the registered bearing.

Figure 1. Cunnington's 1929 plan with the model's marker posts (blue circles) superimposed. Her dashed line runs south-west to north-east at 49.4° true. The orange and green lines are the long axes fitted to rings A–B and C–F. Plan: Cunnington 1929.

The line is drawn at a sunrise bearing through the centre. Nothing on the plan shows it being derived from the posts, and the question is whether the posts agree with it.

Where the rings point

The long axis of each ring was found by fitting an ellipse to its post positions (least-squares conic fit). Uncertainty was estimated by bootstrap: 3,000 resamples of each ring's posts, each post also displaced by a random error of 0.3 m, the fit repeated each time. As a check, the axis of best mirror symmetry of each ring was found independently. It agrees with the ellipse axis to within 3.5° for rings A–E. For ring F the fit is unstable.

Ring	Posts	Size (m)	Long axis	95% range	Short of 49.4°
A	60	44.8 × 40.7	39.7°	35.3–44.1°	9.7°
B	32	39.0 × 34.6	37.5°	32.0–43.2°	11.9°
C	16	29.9 × 25.3	41.0°	32.7–49.6°	8.4°
D	18	23.1 × 19.2	44.4°	34.0–53.3°	5.0°
E	18	18.1 × 14.0	45.2°	35.7–54.6°	4.2°
F	12	11.8 × 8.6	42.7°	26.6–59.7°	6.7°

Azimuths are true (OSGB grid bearing + 0.17°).

Figure 2. The fitted long axis of each ring, with its 95% bootstrap range, against the 2500 BC midsummer sunrise (shaded) and Cunnington's line (dashed).

Every best estimate lies north of the sunrise. None of the rings can point at any sunrise, since 49.4° is as far north as the sun ever rises here. The rings fall into two groups:

• Rings A and B lie about 10–12° north of the sunrise, and their 95% ranges exclude it.
• Rings C–F lie 4–8° north. Their ranges include the sunrise, or in the case of C only just reach it, because rings of 12–18 posts this close to circular do not fix an axis well. If only positional error is allowed for, without resampling the posts, the range for C (35.9–46.0°) also excludes the sunrise, while D (38.6–50.3°) and E (39.4–50.8°) still just include it.

This division matches the suggestion by Chadburn (2010) and Chadburn and Ruggles (2017) that only rings C–F follow the astronomical axis. The fits support it, and add that rings A and B are measurably off it. In Ruggles and Chadburn's grades of precision, C–F sit at the "broadly solstitial" level of about 5°. A–B fall outside it.

The sightline

The Cunningtons watched the midsummer sunrise from the site in 1927 and believed that a gap in the posts could have been used to observe it (The Past, 2025). Along Cunnington's line from the centre, the nearest post centres are as follows:

Ring	Nearest post, NE (m)	Gap centre, NE	Nearest post, SW (m)	Gap centre, SW
F	0.94	46.9°	0.18	238.5°
E	0.30	42.6°	1.07	227.9°
D	1.16	46.5°	0.18	220.8°
C	1.79	45.4°	1.31	223.6°
B	1.04	45.9°	0.37	223.8°
A	0.43	47.4°	0.42	231.0°

Distances are from the post centre to the line. The gap centre is the bearing of the midpoint of the gap the line passes through.

At every ring the line crosses an ordinary inter-post gap. Only ring B's gap is wider than its normal spacing (13.0° against 10.9°), and no corridor is left open along the line. Towards the north-east, the view clears the posts as long as the E posts were less than about 0.6 m across and the A posts less than about 0.85 m. The A posts are estimated at 0.3 m (Marshall et al. 2024). The diameters of the D–F posts are not known. Towards the south-west the line passes 0.18 m from a D post and from an F post, which would block it unless those posts were under about 0.35 m across. The gaps themselves are centred on 42.6–47.4° in the north-east, averaging about 46°, and 220.8–238.5° in the south-west. The open corridor through the rings therefore runs a few degrees north of Cunnington's line, not along it.

Figure 3. The 3D model at first gleam, midsummer 2500 BC, in plan view. The sun ray (yellow) runs along Cunnington's line (white). The fitted C–F axis (green) and A–B axis (orange) diverge from it. Posts are drawn at a uniform 0.64 m diameter.

What this changes

The solstitial axis at Woodhenge is a property of Cunnington's line, not of the timber rings. The line was drawn at the sunrise bearing through the centre of the rings, and the alignment as usually stated derives from it. Measured against the posts:

• rings A and B are oriented about 10–12° north of the 2500 BC midsummer sunrise, and their 95% ranges exclude it;
• rings C–F are oriented 4–8° north of it, which is consistent with a broad solstitial intent but does not establish one;
• the clear sightline along the line depends on post diameters that are known only for rings A–C, and the free corridor through the rings is centred a few degrees further north.

The June post concluded that the long axis of the rings "does point, broadly, the right way". That holds only for the inner rings, and only at the broad end of the precision scale. It does not hold for rings A and B.

Limits

All of the geometry uses marker positions checked against Cunnington's drawn plan, which is itself her record of the holes. An error common to both would not be detected. An ellipse is one model of the ring shape. Thom's egg-shaped constructions define the axis differently and would give different figures. The bootstrap treats posts as interchangeable, which is crude for rings of 12–18 posts. The results would be most improved by the D–F post diameters and an independent survey of the excavated holes.

Sources

• Chadburn, A. 2010. "Case study 2.1: Stonehenge World Heritage Site, United Kingdom." In C. Ruggles and M. Cotte (eds), Heritage Sites of Astronomy and Archaeoastronomy in the Context of the UNESCO World Heritage Convention. Paris: ICOMOS/IAU, 36–40.
• Chadburn, A. and C. L. N. Ruggles. 2017. "Stonehenge World Heritage Property, United Kingdom." In C. L. N. Ruggles (ed.), Heritage Sites of Astronomy and Archaeoastronomy in the Context of the UNESCO World Heritage Convention: Thematic Study no. 2. Paris: ICOMOS, 41–62.
• Cunnington, M. E. 1929. Woodhenge: A Description of the Site as Revealed by Excavations. Devizes.
• Marshall, P., A. Chadburn, I. Hajdas, M. Dee and J. Pollard. 2024. Woodhenge, Durrington, Wiltshire: Radiocarbon Dating and Chronological Modelling. Historic England Research Report Series 94/2024.
• Ruggles, C. L. N. 2006. "Interpreting Solstitial Alignments in Late Neolithic Wessex." Archaeoastronomy 20: 1–27.
• Ruggles, C. L. N. and A. Chadburn. 2024. Stonehenge: Sighting the Sun. Liverpool University Press / Historic England.
• The Past. 2025. "100 years of Woodhenge: tracing an archaeological icon, from discovery to new dating evidence."
• Jenks brothers. 2008. GPS survey of the Woodhenge marker posts (unpublished plan).
• Cross, D. Astronomy Engine (software library).
• Model and data: github.com/TimDaw37/stonehenge-block-3d.