A polished 2-body gravity simulation in your browser — click, drag, and watch orbits unfold.

Live demo: https://soumendrak.github.io/orbital-sim

Features

Newtonian gravity — bodies interact via F = G·m₁·m₂ / r² with softening for stability
Click‑to‑launch — drag from a point to set a body's initial velocity vector
Real‑time trails — fading orbital paths that preserve history
Speed control — slider from 0.1× slow‑motion to 3× fast‑forward
Pause / Resume — spacebar or button to freeze the simulation
Up to 4 orbiting bodies — each with a distinct colour
Hover tooltip — shows mass, velocity, and distance from the central star
Responsive — works on desktop and mobile (touch support)
Keyboard shortcuts — spacebar toggles pause, C clears trails
Body removal — click an orbiting body to delete it
Auto‑cleanup — bodies that escape or crash into the star are removed

How it works

flowchart TD
    A[requestAnimationFrame] --> B{Sim paused?}
    B -->|Yes| C[Draw frame]
    B -->|No| D[Compute elapsed time]
    D --> E[Scale dt by speed slider]
    E --> F[physicsStep]
    F --> G[For each pair:<br/>compute gravitational<br/>acceleration]
    G --> H[Update velocity<br/>symplectic Euler]
    H --> I[Update position]
    I --> J[Record trail point]
    J --> K{Check boundaries}
    K -->|Escaped or<br/>crashed into star| L[Remove body]
    K -->|OK| M[Draw frame]
    C --> N[Render star field<br/>+ trails + bodies<br/>+ tooltip]
    M --> N
    N --> A

Physics details

The simulation uses symplectic Euler integration (velocity updated first, then position), which preserves energy better than naive Euler and produces stable elliptical orbits for appropriate initial conditions. A softening term (ε = 20 px) prevents numerical blowup when bodies pass close to each other.

Usage

Open index.html in any modern browser. No build step, no server required (though a local server helps with some browser policies).

Action	Result
Click and drag	Place an orbiting body with initial velocity in the drag direction
Click an orbiting body	Remove it
Hover a body	See mass, velocity, distance from star
Spacebar	Pause / Resume
`C` key	Clear all trails
Speed slider	Adjust simulation speed
Clear button	Erase orbital trails

Project structure

orbital-sim/
├── index.html    # Single self‑contained HTML file (~25 KB)
├── README.md     # This file
└── LICENSE       # MIT License

Deploy to GitHub Pages

git clone https://github.com/soumendrak/orbital-sim.git
cd orbital-sim
git checkout -b gh-pages
git push origin gh-pages

Then enable GitHub Pages in your repository settings, pointing to the gh-pages branch.

License

Licensed under the MIT License.