iPhone · iPad · Mac · Apple Watch · Apple TV
Antikythera Mechanism Dial brings back the front dial of the Antikythera Mechanism and computes it from the gear ratios of a published reconstruction (Freeth et al., 2021). Turn the crank and watch the Sun, the Moon and the planets move through the centuries.
Video (French labels): Antikythera Mechanism reconstruction by taciclei, CC BY 4.0.
The object
In 1900, sponge divers found an ancient wreck off the Greek island of Antikythera. Among the objects raised in 1900–1901 were corroded lumps of bronze; in 1902, a gear wheel was noticed on one of them. They are the remains of the Antikythera Mechanism, a hand-cranked astronomical calculator built in the 2nd or 1st century BC, the oldest known complex geared machine. Its fragments are kept at the National Archaeological Museum in Athens.
Its front dial showed the positions of the Sun and the Moon, the phase of the Moon and, according to its inscriptions, the planets. This app shows that dial, computed the way its gears computed it.
The dial
The Sun, the Moon with its phase, Mercury, Venus, Mars, Jupiter and Saturn move around the zodiac ring. On iPhone and iPad a wheel runs through hours, days, lunar months and years; on Apple Watch the Digital Crown is the crank.
Tap a celestial body for its card: sign, position, motion and, for the Moon, the phase, the lit fraction and the age. Zodiac and Egyptian month inscriptions in your language or in ancient Greek.
Eclipses
A countdown to the next eclipse predicted by the machine, with what the Saros dial announced: its cell and its glyph. When the real eclipse is known, the app compares the two.
For the annular solar eclipse of 6 February 2027, the machine is 3.3 hours early.
The Mechanism
Underneath, the wheels of the reconstructed mechanism turn with the pointers. Fast playback, back view, exploded view.
Each part shows its status: surviving in the fragments, reconstructed from strong evidence, or hypothetical. The app does not present a guess as a fact. (iPhone and iPad, iOS 18 or later.)
Real sky
Raise your iPhone or iPad: with the compass and the motion sensors, each pointer aims at the real Sun, Moon and planets. Switch between “Sky” and “Machine” to see how far the ancient machine drifts from the sky.
The direction depends on the compass (about 5 to 15°). Your location stays on the device (except, rounded to about ten kilometres, to your own Apple TV when you calibrate it); without it, pick a city. (iPhone and iPad with iOS 18 or later; Apple Watch with a compass.)
One free app
One App Store page, free everywhere, no in-app purchase.
A large dial and, in landscape, a column for the date, the celestial bodies and the crank. Extra-large Home Screen widget. iPadOS 17 or later.
Home Screen and Lock Screen widgets, StandBy, a black bedside mode with a red night palette. iOS 17 or later.
The Digital Crown turns the crank. Always On display, complications and a Smart Stack widget. watchOS 10 or later.
Scroll over the dial to move time, keyboard shortcuts, Time and Dial menus. macOS 14 or later.
The dial on the big screen, the crank on the remote, Real Sky once calibrated with your iPhone or iPad (Apple TV 4K). tvOS 17 or later.
English, French, German, Greek, Spanish, Italian, Japanese, Portuguese (Brazil) and Simplified Chinese.
The app is not a watch face: watchOS does not allow third-party watch faces. It is an app with complications for your watch faces.
Method and proofs
The app follows an open 3D reconstruction of the mechanism, itself built on the published model of Freeth et al. (Scientific Reports 11, 5821, 2021). The reconstruction, its data and its proofs are public.
targets of the gear trains matched exactly, as fractions, with a single degree of freedom (the crank). The Moon turns 254/19 times per year: 254 sidereal months in 19 years.
theorems in Lean 4 (with Mathlib, no sorry) prove the gear trains, the 22 targets and the Metonic, Saros, Exeligmos, Callippic and Olympiad cycles, checked by continuous integration.
of the 69 gears are surviving in the fragments, reconstructed from strong evidence, or hypothetical (after Freeth et al. 2021). The planetary trains are hypotheses, and are labelled as such.
These figures come from the README of the research repository. The Lean proofs check that reconstruction (kinematics, targets, centre distances); a working animation does not prove how the original was built.
Privacy
The app collects no data. No account, no advertising, no analytics, no tracking, no third-party SDK, no internet connection. Your location, if you allow it for Real Sky or Compass, is used only on the device, except that it is sent, rounded to about ten kilometres, to your own Apple TV when you calibrate it: the only link is the optional local one between your own iPhone or iPad and your own Apple TV. This website has no cookies, no trackers and loads nothing from other sites.
Antikythera Mechanism Dial