The Antikythera Mechanism
Turn the crank and the bronze computes: the Sun, the Moon and its phase, five planets, a lunar calendar of 235 months, the four-year cycle of the Games, and a 223-month table of eclipses. Every tooth count here comes from X-ray tomography of the fragments, or from the 2021 UCL reconstruction of the lost front gearing.
Front · the Cosmos
zodiac · Egyptian calendar · ringsRings in the ancient order outwards: Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn, each carried by its own tube. The golden sphere and ray mark the true Sun; the plain pointer is the date on the Egyptian calendar; the double-ended Dragon Hand shows the lunar nodes (hypothetical, Freeth 2021). The Moon's half-silvered ball turns to show its phase. Drag the Egyptian ring to re-set it — it slips a day every four years. Hover over any Greek or Egyptian name for a translation.
Back · calendar & eclipses
Metonic · Games · SarosUpper spiral: 235 lunar months in five turns — the 19-year Metonic cycle — with the Games dial (4 years) and the Callippic dial (76 years) inside. Lower spiral: 223 months in four turns — the Saros — with Σ for a lunar and Η for a solar eclipse, and the Exeligmos dial for the 8-hour shift. A pin in a slot rides the spiral groove outwards. Hover over a cell or an inscription for its meaning.
Inside · 67 gears
3D · measured radiiThe trains
tooth counts → periodModel & limitations
Measured: the surviving gearing behind the Main Drive Wheel b1 — the crank a1 (48), b1 (223), the Moon train with its pin-and-slot lunar anomaly on k1/k2 (about 1.1 mm between axes, pin 9.6 mm out: ±6.5°), the Metonic, Games and Callippic trains, and the Saros and Exeligmos trains (Freeth et al. 2006, 2008). Pitch radii are the CT measurements of Supplementary Table S8 (Freeth 2021).
Reconstructed by Freeth et al. (2021): the front Cosmos — period relations Venus (289, 462) and Saturn (427, 442) read from the Front Cover Inscription, the others derived; gear trains of Fig. 3e–f; pin geometry of Table S9; the ring display; and the Dragon Hand for the nodes, which the authors themselves call hypothetical. Only the 63-tooth Venus gear of Fragment D survives from this part. The planets' motion is Greek epicyclic theory: no eccentricity of their own orbits, which is why Mars can be tens of degrees out near opposition.
This page's own: the year of 365.25 days per turn of b1; the positions of the arbors in 3D (placed by meshing distance, not taken from the CT); the true Sun's eccentricity (Hipparchus's 1/24, apogee 65½°); the Moon phase computed directly rather than through its two unmodelled gears; where the seven intercalary months fall on the Metonic spiral; and the Saros glyphs, marked by a simple rule (a syzygy within 11½° or 17° of a node) where the real dial's 51 glyphs came from a Babylonian scheme. The comparison sky uses JPL's 3000 BC–AD 3000 elements, Meeus's Moon, and ΔT from Espenak & Meeus.
Keyboard: Space run/pause, ← → a day, Shift + arrows a month.