Orrery
Place worlds round a star at a radius and a speed, and find an arrangement gravity lets last a hundred orbits.
4
levels3–12 min
a run, player-paced4
movesNo timer
player-paced, always
Orrery
Place worlds round a star at a radius and a speed, and find an arrangement gravity lets last a hundred orbits.
A star, a supply of worlds, and empty space. Choose each world's distance, its place on the orbit and its speed, then press run — the one commitment. The integrator advances the system a hundred orbits and you scrub through what happened: the orbit that held, the close pass that flung a world away, the moon the star took.
Levels
4 levelsThe tag on each level says how it gets harder. Levels gate on ideas, not on each other — jump wherever it gets interesting.
What decides the outcome
The game never restates the science — it imports it. These are the model layers that do the deciding.
The N-body integrator (velocity Verlet with softening), orbital elements from a position and velocity, circular-orbit speed, Hill-sphere radius, and the masses and lengths in constants.ts — whose G is physics/model/gravitation's. The game states no law of motion of its own.
Why it teaches
The author's own delete-the-science argument: remove this game's substrate and there is nothing left to choose.
Every placement is a gravitation decision judged by the same integrator Astronomy's widgets use: a world that is too fast at its radius leaves, one placed within a few Hill radii of the giant is flung, a moon set near the edge of its planet's Hill sphere is taken by the star, and a world sharing the giant's orbit survives only where Lagrange said it would. Without gravity no placement differs from any other.
Accessibility
The contract's declarations, stated before you commit to a run.
Keyboard
Playable start to finish from the keyboard.
Screen reader
Every move is narrated — the narration is the state, not a description of a picture.
Motion
Reduced-motion variants provided.
Audio
Silent — no sound, and nothing on screen moves on its own.