Live
Live: https://celestial-web-liard.vercel.app Anyone can now open Celestia’s solar system in a web browser, with no install.
Core trick
Ports upstream C++ orbit code to TypeScript, then diffs body positions at 1,003 dates against a compiled C++ reference.
Description
Live: https://celestial-web-liard.vercel.app
Anyone can now open Celestia’s solar system in a web browser, with no install. Celestia is a well-loved open-source space simulator written in C++ with legacy OpenGL. We ported its orbit engine to TypeScript, Next.js and Three.js using Gemini 4 Argon.
We did not just make it look right. We proved it is right. We compiled the original C++ as an answer key. Then we compared every body at 1,003 dates from 1900 to 2100. All 35 bodies match: the Sun, eight planets, Pluto and 25 moons. Most agree to within centimeters. The largest difference is 34 meters, for Phoebe, on an orbit 13 million km wide.
This was tedious work. The planets alone use 10,203 coefficients. Saturn’s moons come from the TASS17 theory, with over 1,100 rows of numbers for Iapetus alone. Argon copied every one of them into TypeScript.
The check also caught real mistakes. Argon dropped 5 identical rows from a 583-row table. Our row-by-row diff found the exact spot. Argon fixed it, and every date matched again.
You can pick any planet or moon and fly to it. You can run time forward or jump to any date. The Verify page shows the accuracy for every body.
Live: https://celestial-web-liard.vercel.app
Code: https://github.com/sreeprasad/celestial-web
Original: https://github.com/CelestiaProject/Celestia
Orbit code ported from Celestia (GPL-2.0-or-later).
Planet textures from Solar System Scope (CC BY 4.0).
README excerpt
# Celestia in the Browser Celestia's solar system, running in any web browser with no install. Built for the **Gemini 4 Argon Hackathon** (San Francisco, October 2026). **Try it live:** https://celestial-web-liard.vercel.app **Original Celestia:** https://celestiaproject.space ([source code](https://github.com/CelestiaProject/Celestia)) ## What it is Celestia is a well-loved open-source space simulator. We ported its orbit engine to the web with Gemini 4 Argon. You can: - See the Sun, all 8 planets, Pluto and 25 moons. - Fly to any planet or moon with one click. - Run time forward, pause, or jump to a date. - Make small bodies easier to see with the size boost. ## It matches the original We ran Celestia's original orbit code as an answer key. Then we compared our version against it for 35 bodies, at 1,003 dates from 1900 to 2100. - **35 out of 35 bodies match** within 1 km on every date. - Most agree to within a centimeter. - The largest difference is Phoebe, a moon of Saturn: 34 meters, on an orbit about 13 million km wide. The **Verify** page in the app shows the result for every body. ## How Gemini 4 Argon helped Argon did the porting: 1. It read Celestia's original orbit code and set up the answer key. 2. It ported the orbit math for the planets. 3. It ported Pluto and 25 moons, copying their long tables of numbers by hand. Iapetus alone has over 1,100 rows. 4. It built the 3D app. 5. It fixed its own mistakes when we sent back the check results. The check