Platonic Clock

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Year

This turn:

Click or drag on the clock to choose a year. Arrow keys step 10 years (Shift: 100, PgUp/PgDn: 1,000). The buttons under the clock change turn.

Events around

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Import…

Sky

Centre: South ecliptic pole

Faintest stars Field radius Fisheye Stars move with the year Constellation boundaries Constellation names Bright star names Event labels on the clock Magellanic Clouds Theme

How to read it

You are looking up at the sky, centred on the south ecliptic pole (the hub). The hand turns once every 25,800 years (Plato's "great year"), uniformly, the way a clock shows mean time. The south celestial pole itself (the small orange ring on the dotted track) circles the hub at a slightly varying speed, so it runs a little ahead of or behind the hand. Its nearest star, the pole star, is ringed in red. Seen from the south, the clock runs clockwise. Flip pole centres the north ecliptic pole instead; the hand then follows the north celestial pole and runs anticlockwise. The Fisheye slider changes the projection: the middle setting keeps distance from the centre proportional to angle on the sky (equidistant). Flatter settings stretch the edge (stereographic is shape-true), and stronger fisheye squeezes it (equal-area, then orthographic, like a globe).

The outer ring is the zodiac along the ecliptic (13 constellations, IAU boundaries). The markers outside it are the equinoxes and solstices of the chosen year; the ♈︎ March equinox marks the astrological "age".