Physics state
What stays real
a = G * source_mass / distance^3 * displacement
Double-precision positions, velocities, masses, and radii stay in physical units inside src/sim.
C · raylib · WebAssembly
A solar system simulator you can run and inspect.
This is a small, physics-first C project: Newtonian gravity in SI units, parent-relative moons, persistent trails, and a raylib renderer compiled to the browser.
C11raylib 3D boundaryvelocity-Verlet / kick-drift-kick8 bodies now
Current orbit sketch
Not to scale. The real state lives in meters; this sketch only makes the implemented catalog visible.
Catalog8 implemented bodies
Integratorvelocity-Verlet / kick-drift-kick
UnitsSI units: m, kg, s, m/s
RuntimeNative C loop plus Emscripten callback loop
ControlsTab/C focus, V scale mode, mouse-wheel zoom
ArtifactsHTML, JS, WASM checked before Pages deploy
Why this exists
A learning lab, not a fake mission-control dashboard.
The interesting part is the boundary between math and picture: the simulator keeps bodies in meters, kilograms, seconds, and meters per second, then deliberately bends only the rendered view so planets, moons, labels, and trails remain readable.
Simulator
Run the actual C/raylib build in the page.
The embedded app below is the WebAssembly artifact from the build pipeline. Use it as a working lab bench, then jump into the docs when you want to see how the physics and rendering are separated.
Controls:Tab/C focus bodyV scale modeMouse wheel zoom
Rendered view
What gets bent
Illustrative scale, moon separation, labels, camera focus, and trails are renderer choices, not changes to simulation state.
Trace the simulation coreBodies in the scene
Eight bodies, with parent relationships kept explicit.
Moons are initialized relative to their parent body, then added to the same shared gravity simulation.
SunStarParent: NoneFixed origin anchor for the current heliocentric baseline.MercuryPlanetParent: SunHeliocentric perihelion position with vis-viva tangential speed.VenusPlanetParent: SunHeliocentric perihelion position with vis-viva tangential speed.EarthPlanetParent: SunHeliocentric perihelion position on the +Z axis with vis-viva speed.MoonMoonParent: EarthEarth-relative perigee offset added to Earth absolute state.MarsPlanetParent: SunHeliocentric perihelion position on the -Z axis with vis-viva speed.PhobosMoonParent: MarsMars-relative periareion state added to Mars absolute state.DeimosMoonParent: MarsMars-relative periareion state added to Mars absolute state.
Current state
Working, but honestly still early.
- Working now: Sun, Mercury, Venus, Earth, Moon, Mars, Phobos, Deimos, focus cycling, zoom, scale modes, and persistent trails.
- Still intentionally missing: outer planets, textures, shaders, ephemeris-accurate state vectors, and barycentric Sun motion.
- Next steps stay small: one body or rendering improvement per iteration, with tests and docs updated beside the code.
Source references
Where the page gets its claims.
01Physics modelNewtonian acceleration and velocity-Verlet stepping live in src/sim.
src/sim/physics.c02Body catalogStable BodyId and parent metadata keep renderer, labels, and docs aligned.src/sim/solar_system.c03Rendering boundaryraylib conversion handles readable scale without mutating physics state.src/render/renderer.c04WASM pipelineEmscripten artifacts are checked before Astro publishes them.tools/check_wasm_artifacts.py05Astro docsThe dedicated docs section explains the code as a maintained public notebook.docs/src/pages/docs/