Orrery

Compare the relative radii and orbital periods of Mercury through Mars in a schematic top-down circular model. Enter simulated days, select a planet, or start/pause the animation. Playback speed is simulated days per real second. Editing time pauses and clears trails; reset returns to day 0. Time advances continuously without the old four-year reset. It stops at 1,000,000 simulated days.

Orbit radii share a linear AU scale; the scale bar adapts to the zoom. Sun and planet sizes are exaggerated. Initial phases 0°/90°/180°/270° spread out the diagram and are arbitrary, not real sky positions. No calendar date is implied.

Rounded mean radii and sidereal periods give nearly equal T²/a³. Circular speed is 2πa/T; the displayed angle changes uniformly, with a full turn after each period. Real eccentricity, inclination, gravitational perturbations and changing speed are omitted. For ephemerides use the planetary positions tool. Trails use at most 160 time samples and follow circular arcs even at low frame rates or after resizing. They show at most one complete orbit. Hidden tabs pause the simulation.

Ctrl/⌘ + wheel zooms around the centre; drag to pan. With the plot focused, +/− zoom, arrow keys pan and 0 fits the view. Reset also returns time to day 0. Open Orbit data for numeric values and Kepler’s law. PNG exports the current view. Only entered time, speed, selected planet and trails preference are retained; animated time, trails and view are not saved.