henge

Geometry and alignments

Surveyed geometry — Established

The figures the app computes with, as encoded in HengeGeometry/Monument.swift (Cleal et al. 1995; Petrie’s and later surveys):

Feature	Figure
Monument axis	azimuth 49.9° (NE, to the midsummer sunrise quarter)
Sarsen circle	33.0 m diameter, 30 uprights
Aubrey ring	87.0 m diameter, 56 holes
Enclosure earthwork	~110 m across (ditch centreline)
Heel Stone	77 m out along the axis, 4.7 m tall
Avenue	22 m wide, straight for ~500 m before turning
Station Stones	four, on the Aubrey circle, forming a rectangle

• The station rectangle’s short sides parallel the main axis; its long sides run toward the major standstill moonrise/moonset quarters — this much is geometry anyone can redo from the plan. Whether it was designed for the moon is Debated (see the lunar page).
• The axis alignment itself — midsummer sunrise up the Avenue, midwinter sunset the other way — is Established: it is the plan, not a theory about the plan.
• Cardinal directions: the app’s overlay draws true north from the ephemeris frame, not magnetic.

The stonehengeology.com constructions — Speculative

Source: stonehengeology.com/stonehenge-geometry (fetched 2026-07-31, at the owner’s direction). One author’s geometric reconstruction in the tradition of Alexander Thom’s “Megalithic Yard” (MY); enthusiast work citing real surveys (John Wood 1740, Petrie 1880, Gowland 1901, Hawley and Atkinson) but presenting derived constructions as demonstrated fact, without peer review. Every claim below is Speculative and must be badged wherever the app shows it.

Claims, as made:

• Sarsen circle diameter = 36 MY; 30 stones at 12° spacing with 4° gaps; primary axis azimuth 50°.
• An outer bluestone oval “dedicated to the moon”: two 27-MY-diameter circles with centres 2 MY apart (envelope 27 × 29 MY, sum 56 — read as the 56 Aubrey holes and a “56-year moon cycle”), its axis offset 24 megalithic inches from the sarsen centre, aligned on the southernmost moonrise / northernmost moonset.
• An inner bluestone oval “dedicated to the solstice”: 14.5 × 18 MY, built from four near-Pythagorean triangles (3.5 : 7.25 : 8 MY), on a secondary axis through trilithons 3 and 4.
• A central 3:4:5 triangle (18:24:30 megalithic inches); the Altar Stone 6 MY long, one sixth of the sarsen diameter; the station rectangle “1,920 times” the core triangle’s volume.
• Aubrey holes 56 and 28 said to have held timber posts fixing the axis five centuries before the sarsens.

What survives contact with the established register: the axis azimuth (50° against the surveyed 49.9°), the stone count, the 56, and the station rectangle’s lunar bearing — all of which the app already carries from better sources. The Megalithic Yard itself is rejected by mainstream archaeometry (Thom’s unit does not survive statistical re-analysis); the ovals and triangle constructions are the author’s own.

In the app: the geometry overlay draws the established table above with labels and ground-mapped measurements; the speculative constructions, if shown, ride the same hypothesis badging as the Hoyle markers.

The lunar hypotheses — Debated

See research/lunar-markers.md: Hawkins (1963/1965) and Hoyle (1966) on the Aubrey ring as an eclipse predictor. The app’s gold-marker mode acts out Hoyle’s machine and says so on screen, every time, with the honest scorecard (42 caught, 0 missed, 9 false alarms over a test decade). Hawkins’s specific mechanics still need primary-source pinning before any in-app prose uses them.