Antikythera Cosmos

The oldest geared computer in the world, rebuilt from its tooth counts and turned by one crank in your browser.

Open the exhibit · Landing page · How it is built · How the numbers are checked

A working 3D reconstruction of the Antikythera mechanism, after the 2021 "Cosmos" model by Tony Freeth's team at UCL: 69 gears, the eight nested outputs of the front dial, and the Metonic, Callippic, Games, Saros and Exeligmos dials on the back. It is built parametrically in Blender 5.1 from a single gear table, exported as glTF, and driven date by date in the browser, beside a column that holds what the machine predicts against what really happened.

69 gears, every one cut from data/gears.json	30 of them survive in the bronze fragments
223 teeth on the main wheel, one turn a year	254/19, the Moon's ratio, exact in the gearing
51 eclipse glyphs (Freeth's 2014 reconstruction), held against NASA's canon	14 leaves in the narrated walkthrough

Thirty of the wheels are the ones found in the fragments and thirty-nine follow the 2021 model; the pointers go where that model says the bronze would have put them. Every rate is an exact fraction of the tooth counts, and the landing page lists where this copy departs from the 2021 model. When the machine is wrong, the exhibit says so.

The walkthrough

The exhibit opens with fourteen leaves, narrated by David, each setting the machine to show one idea. Here they are as stills.

1. A machine that models the sky. Sixty-nine gears on one crank: thirty from the fragments, thirty-nine from the 2021 model.	2. What the divers found. Fragment A, the largest piece, from a CT scan of the original.
3. Seeing inside the corrosion. The reconstruction laid inside the scan, so the wheels show through.	4. One crank, one year. A 48-tooth crown wheel against the 223-tooth main wheel.
5. Why everything is counted from an epoch. The machine has no clock; it was set once, by hand.	6. The front dial is the sky. The zodiac, the Egyptian calendar and the parapegma.
7. The Moon and its phase. Exactly 254/19, and a half-dark ball that turns once a month.	8. The pin and slot. Two gears 1.1 mm off axis make the Moon speed up and slow down.
9. The calendars on the back. The Metonic spiral, the games, the Callippic cycle.	10. Predicting eclipses. The Saros spiral, its glyphs checked against NASA.
11. The planets. Rings for the planets and the true Sun, each planet with its own epicyclic gearing, a coloured stone and the proposed index letters.	12. The sky it tracks. Each body on its epicycle, looping backwards.
13. How good was it? The Moon within about three and a half degrees near the epoch, its slow drift, planets that keep their long cycles but not their loops, and the caveat about hand-filed teeth.	14. Explore. Drag, zoom, click a gear, wind the crank, send the view as a link.

Seven ways to look at it

Every view is a switch in the exhibit and every one can be sent as a link. These are filmed from the running page; each opens the exhibit in that view.

The front dial. The zodiac, the Egyptian calendar (365 days, as the 2021 model has it), and the 2021 model's cosmos: rings for the planets, the true Sun and the date, with their index letters, under the Moon pointer and the Dragon Hand.	The back dials. The Metonic and Saros spirals, cut as slots for the pointers' pins to ride in, with the games, Callippic and Exeligmos dials.
Taken apart. Every wheel slides out along its arbor and keeps turning, so the trains that share the great b1 wheel can be told apart.	Only what survives. The thirty gears found in the fragments, solid; the thirty-nine reconstructed ones as ghosts.
The sky it tracks. The machine's cosmos drawn from its own gears; bronze is what the machine shows, verdigris the real sky.	The manuscript. The same exhibit as a scholar's copy of Ptolemy: parchment, iron-gall ink, red ochre, gold leaf for the Sun.

What a visitor can do

• Turn the crank at a day, a month, a year or ten years a second, drag the handle to wind it by hand, or press the space bar; jump to the next eclipse, type a year, or press today and see how far twenty-two centuries have carried the pointers (the Sun a few degrees, the Moon over a hundred).
• Hover a gear for its tooth count and rate; click it to see its train alone. Inside lifts the plates away; Taken apart spreads all 69 wheels along their arbors, still turning; only what survives shows the thirty gears found in the fragments with the reconstructed ones as ghosts; the Fragment A slider crossfades to the CT scan of the real bronze.
• Sky draws the machine's own cosmos with the retrograde loops and the true sky beside it; the Moon panel is lit from where the machine's Sun pointer stands, and can be turned to the real Moon's libration.
• A narrated fourteen-leaf walkthrough; Share copies a link to whatever is set up, and on a phone opens the share sheet; save this view keeps the stage as a picture; the exhibit installs as an app and opens offline once visited.
• Two versions of the same exhibit, switchable in the top bar: the vitrine (a museum gallery at night, the default) and the manuscript (?theme=manuscript). They share every gear, number and panel; only the room, the page and the inks differ.

Every state is in the address: ?view=front|back|iso|crank|pinslot|front-close|back-upper|back-lower, &years=, &epoch=, &inside=1, &apart=1, &survives=1, &sky=1, &expose=1, &lib=1.

How the numbers are checked

• python/tests/test_ratios.py asserts every pointer rate as an exact fraction (254/19, 940/4237, −5/93, 1513/480 …) from the tooth counts alone.
• blender/build_all.py re-verifies the Blender rig by driving it and reading back every gear, and checks the pin-and-slot amplitudes against asin(d/r); build/rig_dump.json holds the report.
• web/src/astro/eym.test.ts reproduces the 51 / 38 / 28 glyph counts and every glyph observed on the surviving Saros dial (Freeth 2014 Tables S1, S2).
• The eclipse ledger holds each month the machine predicts against 23,962 rows of NASA's Five Millennium Canon, and says plainly when the machine is wrong.
• 70 tests in all: cd python && python -m pytest (36), cd web && npx vitest run (34).

How it is built

data/gears.json          every gear: teeth, module (Freeth 2021 Table S8), arbor, layer, couplings
data/eclipses_*.json     NASA Five Millennium Canon (Espenak & Meeus), slimmed
python/mech/             exact rational ratio solver, arbor layout, tooth outlines,
                         Freeth 2014 eclipse-year glyph model, Julian Day maths  (pytest)
tools/gen_dial_textures.py   dial faces drawn in millimetres (zodiac, calendar, spirals, glyphs)
tools/narration.py       the walkthrough's narration (ElevenLabs, the voice "David - Documentary", v3 model)
tools/gen_icons.py       launch icons, the share image and the no-WebGL still
tools/landing_clips.py   the project page's clips, from frames filmed off the running exhibit
blender/build_all.py     gears + drivers (one master property drives everything)
blender/dials.py         plates, dials, pointers, rings, tubes, case, crank
blender/surface.py       UVs, textured bronze, baked ambient occlusion
blender/export_glb.py    static GLB with the driver rules as node extras
web/                     Vite + TypeScript + three.js exhibit
site/                    the landing page: a museum exhibit in five rooms (Cloudflare Pages)
docs/                    the older project page, renders, screenshots, clips, plans and research digests

Rates are rotations per year of b1, clockwise seen from the front positive. The same rule is written three times, in Python, in the Blender drivers and in the web GearGraph, and the three are held together by the tests: the glTF carries every driver rule as am_* node extras, so the browser turns the machine from the same arithmetic Blender did.

Time is Julian Day throughout, on the proleptic Julian calendar for BC dates and astronomical years (205 BC is −204). The epoch is the full moon of 12 May 205 BC (Carman & Evans; Freeth, both 2014), with 22 Dec 178 BC (Voulgaris) as a switch; nothing in the exhibit uses a JavaScript Date.

Running

The exhibit alone needs nothing but Node:

cd web && npm install && npm run dev        # http://localhost:5177

The machine rebuilds headless with Blender 5.1 closed, in two invocations:

python tools/gen_dial_textures.py
python tools/gen_surface_maps.py
blender -b --factory-startup --python-exit-code 1 --python blender/build_all.py -- --out build
blender -b build/antikythera.blend --python-exit-code 1 --python blender/dials.py --python blender/surface.py --python blender/export_glb.py
cd web && npx gltf-transform optimize ../dist/antikythera.glb public/models/antikythera.glb --texture-size 2048 --compress meshopt --texture-compress false --palette false --join false --flatten false
cd web && npx gltf-transform webp public/models/antikythera.glb public/models/antikythera.glb --quality 90
cd web && npx gltf-transform meshopt public/models/antikythera.glb public/models/antikythera.glb --level medium

Hero renders (Cycles): blender -b build/antikythera.blend --python blender/hero_render.py writes docs/renders/*.jpg; then python tools/gen_icons.py refreshes the share image.

Deploy: the exhibit and the landing page go out together to the Cloudflare Pages project antikythera (https://antikytheraexhibit.com, the exhibit at /, the landing page from site/ at /landing): cd web && npm run build && cd .. && node tools/build-pages.mjs && npx wrangler@4 pages deploy site-dist --project-name antikythera --branch main. If the GLB or a texture changed, bump CACHE in web/public/sw.js first so the service worker lets the new copy through; if a landing clip changed, bump the ?v= on its address in site/index.html. The first address, antikythera.stewartgregerson.workers.dev, is now a Worker (worker/redirect.js) that forwards to the domain. The older project page address on GitHub Pages (docs/index.html, served from main /docs) now redirects to the landing page.

NEXT_STEPS.md is the maintenance guide, NOTES.md the decisions in order, CLAUDE.md the rebuild order and the conventions that must not drift.

Attributions

• Reconstruction: Freeth, Higgon, Dacanalis, MacDonald, Georgakopoulou & Wojcik, A Model of the Cosmos in the ancient Greek Antikythera Mechanism, Sci. Rep. 11:5821 (2021), CC BY 4.0, and the earlier AMRP papers (Freeth et al. 2006, 2008, 2012, 2014).
• Eclipse ground truth: "Eclipse Predictions by Fred Espenak and Jean Meeus (NASA's GSFC)", Five Millennium Canon of Solar and Lunar Eclipses. Ephemeris: astronomy-engine (Don Cross, MIT).
• Parapegma and front dial inscriptions: Bitsakis and Jones, "The Front Dial and Parapegma Inscriptions", Almagest 7.1 (2016), CC BY-NC 4.0.
• The games and the calendar: Iversen 2017, Hesperia 86. The calendar ring's holes: Budiselic et al. 2020 (the measurements) and Woan & Bayley 2024 (their statistical analysis). The teeth: Edmunds 2011 (JHA 42) and Szigety & Arenas 2025 (a preprint simulating his error estimates).
• Epochs: Carman & Evans 2014 and Freeth 2014 (12 May 205 BC); Voulgaris, Mouratidis & Vossinakis 2023 (22 Dec 178 BC).
• Fragment A's CT scan: Ashkan Pakzad, CC BY 4.0. The Moon's face: NASA's CGI Moon Kit (LROC colour mosaic), public domain. Rooms: Poly Haven HDRIs studio_small_09 and artist_workshop, CC0. Layout reference: Thomas Weibel's CC BY reconstruction (thomasweibel.ch).
• Narration: ElevenLabs, the library voice "David - Documentary".

The parapegma's Greek wording and the Saros glyph hours beyond the surviving cells are schematic reconstructions; the index letters stand where Bitsakis and Jones 2016 place them (see NOTES.md). Built by Stewart Gregerson with Claude Code.

Licence

Code is MIT (see LICENSE). Third-party assets listed above keep their own licences.