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.

Woodhenge - The 3d Model

 

An interactive 3D model of Woodhenge, accurately georeferenced with the sun, sky and moon modelled over the age of the monument: https://timdaw37.github.io/stonehenge-block-3d/woodhenge/

Stonehenge - The Complete 3D model

 

Autumn Equinox Sunrise

Stonehenge, rebuilt stone by stone and set moving: timdaw37.github.io/stonehenge-block-3d is a free, interactive 3D model of the monument, built from survey-locked stone positions on real LiDAR-derived ground — open it in a browser and walk around all 93 stones, or watch the sky itself move over them.

The sun and moon travel across the horizon in real time, not as a fixed marker: a time slider and "Sun's arc" / "Moon's arc" controls animate the rise, with Gleam, Half orb, and Full orb settings for exactly when a disc counts as up.

An Epoch control swings the whole sky between Modern and 2500 BC, or any year typed in. Go back to 2500 BC and the pole star marker moves too — from Polaris to Thuban — the slow wobble of the Earth's axis, not a rounding error.

A Newham mode draws the station stones' own sightlines — long sides for the moon's furthest rising and setting points, short sides for the solstice sun — as lines running through the stones themselves, with Most Northerly / Most Southerly toggles for the moon's extremes, and a readout comparing the stone-pair bearing against the live sky azimuth side by side.

A Complete view shows the monument with a theoretical complete sarsen build: every lintel in place, the fallen stones ghosted rather than erased. Terrain, orbit and top-down views, and hover-for-coordinates in both OSGB and WGS84 are built in throughout.

Source and data are open on GitHub.

Ramson Cliff erratic: a second thin section still points Cornubian, not glacial

A second thin section, same answer: still more Cornubian than glacial.

Prof Slack has kindly loaned a second thin section cut from the original hand specimen of the Ramson Cliff (Croyde) epidiorite — the ~700 kg block at ~80 m OD on Baggy Point. Discussion with Dr Mik Markham, who knows Cornubian greenstones and the axe-head groups as well as anyone, prompted a fresh transmitted-light description. It confirms the account in Daw, Ixer & Madgett (Quaternary Newsletter 167, 2026) with only small corrections.

The rock is a highly altered ophitic microgabbro with relict clinopyroxene, no olivine and no quartz. Secondary minerals are dominated by brown-green hornblende and colourless-to-green actinolite, two generations, with actinolite the later, and by minor chlorite, epidote and clinozoisite. Biotite and white mica were not confirmed. That assemblage matches the outer aureole of the Dartmoor Granite as described in the BGS Okehampton memoir, and is consistent with Cornubian contact metamorphism more broadly. It does not match non-aureole Devon or Cornish greenstones, which reach actinolite grade only and carry albitised, sericitised feldspar; nor does it match the Welsh Ordovician metadolerites on the Irish Sea route. A Scottish Dalradian source cannot be excluded on the amphibole evidence alone, but remains less likely on transport grounds; further tests on the relict pyroxene chemistry and plagioclase composition would settle it.

What has not changed is the emplacement argument. The block has been used as evidence that Irish Sea ice reached ~80 m OD on this coast. That reading was already thin: first recorded standing upright in pasture in 1969, absent from earlier maps and photographs, angular and unabraded, and the only claimed erratic on the south Bristol Channel shore above ~30 m OD. A Cornubian source does not prove human movement, but it does make a lone high-level glacial drop even less likely. A second slide from the same specimen does not turn an isolated, poorly documented boulder into proof of high-level ice, nor into a stepping-stone for glacial bluestones on Salisbury Plain.

Full description below.

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Rob Ixer's Analysis

A second thin section from the original hand specimen was generously loaned by Prof Slack and prompted discussions with Dr Mik Markham, an authority on Cornubian greenstone axes and on the petrography of Cornubian altered greenstones.

A petrographical examination of it confirmed the original petrographical description (Daw et al. 2026) albeit with some minor corrections. The un-named green amphibole is identified as actinolite. Trace amounts of white mica/muscovite and mixed muscovite-chlorite were not confirmed (the latter was probably misidentified mixed chlorite–limonite-stained chlorite) but trace amounts of epidote with high interference colours were. The suggestion that the rock could be Cornubian in origin is maintained.

The rock is a highly altered microgabbro, hence locally plagioclase–pyroxene have their characteristic ophitic relationship. It comprises relict primary pyroxenes showing both high and low interference colours, unaltered to highly altered plagioclase feldspar, and skeletal and equant-shaped opaques including probable titanomagnetite. The degree of alteration varies on a small scale and secondary alteration minerals are dominated by brown-green amphibole (‘hornblende’) and green actinolite and minor chlorite, with trace amounts of titanite, epidote and clinozoisite. White mica, if present, is very rare. Amphiboles replace and pseudomorph pyroxene but also occur as discrete and distinctive fine-grained mosaics intergrown with chlorite and enclosing very minor titanite, possible zircon and feldspar (perhaps albite). Texturally there is a strong suggestion of more than one generation of amphibole, with actinolite being the later.

Unzoned polysynthetically twinned plagioclase is variably altered from largely unaltered to highly altered, hence much relict feldspar is present. The main alteration is to fine-grained actinolite crystals, with this alteration initiated along cleavage and twin planes. Very minor amounts of chlorite, epidote with high interference colours and probable clinozoisite with low interference colours accompany actinolite. Plagioclase altering solely to fine-grained clinozoisite is rare; fine-grained white mica could not be positively identified.

Pyroxene displaying both high and low interference colours is the only primary mafic mineral; no olivine or pseudomorphs after olivine are present. Relict pyroxene is enclosed within lower-relief amphibole; both are in optical continuity. Much pyroxene is altered to colourless to grey-brown-green amphibole with a good cleavage and with very fine-grained titante lying along that cleavage; this amphibole is enclosed within green actinolite rims. Amphibole fringes about pyroxene are absent but total replacement is common. Other pyroxenes are altered to green actinolite along cleavage and fracture planes or to mosaics of fine-grained stubby actinolite. Locally pyroxene with low interference colours is altered to amphibole with unusual yellow interference colours.

Although a positive identification of the opaques is not possible in a normal thin section, their habit (equant and skeletal) and texture (abundant opaque ilmenite laths within a less opaque different phase; titanite replacing magnetite) strongly suggest the presence of altered titanomagnetite. Lobate opaques that would suggest ilmenite are absent. Opaques are replaced/pseudomorphed by actinolite and an opaques–actinolite association is widespread.

Pleochroic colourless to green actinolite (brown-grey-green amphibole is absent from this association) forms mosaics comprising euhedral to subhedral blocky crystals. Although some replace/pseudomorph pyroxene and opaques, most infill spaces between plagioclase laths; all mosaics are fine-grained but they vary in grain size between aggregates. Some just contain actinolite, others actinolite in minor chlorite, and a few are chlorite-rich with actinolite laths, often radiating, growing into the chlorite. Trace amounts of titanite, a high-relief accessory mineral within its pleochroic halo (zircon perhaps) and small twinned feldspar with fluid inclusions (possibly albite) are present but rare.

Colourless to very pale green pleochroic chlorite with blue and very rarely brown interference colours is the second most abundant secondary mineral after amphibole in amount, but is uncommon. It forms thin cross-cutting veinlets or occurs as a very minor secondary mineral in plagioclase. Most chlorite occurs as short stubby crystals surrounding stubby actinolite or as the main phase enclosing actinolite laths and enclosing minor titanite and possible albite. Some chlorite laths are intergrown with a phyllosilicate with high interference colours; although superficially it looks like muscovite, it may be limonite-stained chlorite. Biotite and positively identified muscovite were not recognised.

Trace amounts of titanite may replace primary iron–titanium oxides or lie along cleavage planes in pseudomorphing amphibole. Small euhedral rhombic titanite is present within stubby actinolite–chlorite segregations.

Very minor amounts of high-relief epidote form thin laths along twin planes in plagioclase; other high-relief epidote-group minerals with blue interference colours are visually identified as clinozoisite.

Trace amounts of sulphide, now altered to limonite, are associated with actinolite mosaics.

Possible zircon has a pleochroic halo when enclosed in actinolite.

This new petrographical description continues to allow the possibility that the erratic is Cornubian in origin, namely a microgabbro that has suffered contact metamorphism from the underlying granites. It cannot be matched to any of the main IPG Group Cornubian axe groups (Groups I–IV), but nor can many Cornubian axe-heads.

Stonehenge Access All Areas - all the way to 11- the final episode (for now)

Stonehenge 3D Model

Stonehenge 3D Model — deceptively simple

It looks like a toy. Grey boxes, a blueish ring, pink Altar, two bright silver station markers. Orbit with a finger. Tap for coordinates. Switch the sun and moon between today and c. 2500 BC.

Under the Minecraft-box look is a finished layout of the stones — each one placed and sized so lintels sit on uprights — on LiDAR-derived ground that rolls out to the horizon when you turn Terrain on. Tap or hover for OSGB / SU / WGS84 coordinates (same language as the stonehenge-plan page, without draping a plan drawing under the model). Sky controls aren’t just decoration: sunrise and sunset by day of year, moonrise and moonset on a most-northerly ↔ most-southerly dial, with an Epoch switch so the azimuths use the Earth’s obliquity for Modern or for around 2500 BC (flat-horizon geometry, stated plainly).

Phone-friendly controls that tuck away. Labels you can turn on. Coords you can pin. No app store, no login — just open the link.

I’m publishing it as a public baseline others can fork and improve (TimDaw37/stonehenge-block-3d). The hard part was getting the stones to sit true on real ground and the tools to stay quiet. The easy part is what you get to do with it.

I am seriously impressed by this model, there are layers of features built in to an accuracy that no other model has. Have a play.

Brimham Rocks and the Devil's Arrows