Ephemeris

🪐 Ephemeris — a real-time 3D solar system simulator, built from scratch

What I made:
A desktop app (Tauri + TypeScript + Three.js) that simulates the solar system from real NASA JPL Horizons initial conditions. Instead of faking the orbits, it actually integrates Newtonian gravity in real time. I hand-implemented three classic computational-physics algorithms: a Velocity Verlet symplectic integrator for stable long-term orbits, a 3D Barnes-Hut octree for O(N log N) gravity, and a Newton-Raphson solver for Kepler's equation to read out live orbital elements.

What was challenging:
The trickiest part was the tension between the symplectic integrator and the Barnes-Hut approximation — every time the octree rebuilds, tiny force discontinuities break symplecticity and energy drift creeps back in. Getting the numerical stability right (gravity softening near close encounters, sub-stepping at high time-acceleration, and removing barycenter drift) and killing GC frame spikes with an octree node memory pool took a lot of iteration.

What I'm proud of:
It genuinely runs on real NASA data and the orbits come out physically correct — the unit tests recover the actual JPL inclinations. And it looks nice too: procedural planet textures, age-faded orbit trails, Saturn's rings, Earth's atmospheric glow, and real axial tilt + rotation.

How to test it:
Open it and the 8 planets load automatically. Drag the time slider to speed things up (1 day/s → 1 year/s), click any planet to see its 6 live orbital elements, then toggle the asteroid belt on (1k–10k particles) and switch between naive O(N²) and Barnes-Hut to watch the FPS difference. You can also pause, reverse, and jump through time.