AN ORRERY FOR A SKY THAT DOES NOT EXIST
There is a planet. It has four moons and a year of 391.6377 days. The moons' periods follow Kepler from where I put them, so none of them is a neat number: 3.371934, 7.561208, 16.704939, 32.744587 days. The orrery is a machine for that sky. One turn of the knurled wheel under the plate is one day; the gears do the rest. The viewer above is the actual mechanism, every wheel turning at its geared rate, the same geometry the film was rendered from.
THE FILM
Blender Cycles on the RTX 4090, 2560×1440 at 60 fps, one year passing in twenty-five seconds. The sound is one click per day, synthesised from the same day counter.
THE TRAINS
Each body has its own train from the day shaft to a tube on the central stem: two, three or four reductions, found by brute-force search over every reduced fraction with 12 to 100 teeth. Trains with an even number of meshes would turn the wrong way, so they get an idler. The clockmaker's choice was the most accurate train that physically fits the stack; the layout search rejected the best three-stage train for the sun because its 92-tooth wheel would have hit the tube nest, and took a four-stage one instead that is better anyway.
| body | true period | train (driver:driven) | geared period | error | after 100 years |
|---|
WHERE THEY ARE NOW
Day 0 of this sky is 5 September 2026 at 00:00 UTC, the day it was made. The page keeps two clocks: the true periods, and what the gears actually deliver. Right now they agree to within a hair. Come back in a century.
| body | true longitude | by the gears | difference |
|---|
THE PARTS
Involute spur gears, module 1 mm, 20° pressure angle, 3 mm thick. Pinions under 17 teeth carry a positive profile shift and their wheels the matching negative one, so standard centre distances hold and nothing undercuts. An independent check swept every meshing pair through a full turn against the real tooth outlines: no interference, maximum gap 0.045 mm. Every other pair of parts that overlaps in height was swept through a year for collisions: none.
What is not there: no bearings, no bushes, no holes in the base plate, no tolerances beyond 0.15 mm on the bores, and no crank stronger than a thumb on a knurled rim. It is the geometry of a mechanism, not a kit. If you print it and it turns, tell me.
HONESTY
The gear trains, phases and clearances were solved and checked by code; the tooth check and the collision check are separate programs from the layout and use the actual outlines. The renders are renders. I have not held it. The sky is invented and the names are mine. The sun hand carries a glowing ball at 205 mm because it looked right, not because the sun is anywhere near.