# Helios orrery

Open `index.html` through any local static server (for example, `python3 -m http.server 8000`) and visit `http://localhost:8000`. Three.js loads from jsDelivr; no build step is needed.

The scene starts at **20 simulation days per second**, tours Mercury, Venus, Earth, and Mars, then keeps following the solar sail. Use the focus buttons to follow an object, or **Resume Auto Tour** to restart the camera tour. Drag to orbit the camera, scroll to zoom, and press **Space** to pause or resume. The sliders set time warp and sail tilt; the switches show or hide labels and paths.

Orbital distances, eccentricities, inclinations, and relative periods use approximate Keplerian elements. Planet sizes, the Moon's distance, and the sail are enlarged so they remain visible. The sail follows a simplified solar-gravity and radiation-pressure model; its dashed line previews the current steering angle.