Each planet follows a real Kepler ellipse: mean anomaly M = M0 + n·t advances at the rate fixed by Kepler's third law, n = 2π/T, where T is the planet's real sidereal period (Mercury 88.0 d out to Neptune 60,190 d). Kepler's equation M = E − e·sin(E) is solved for the eccentric anomaly E by Newton's method each frame, then converted to true anomaly and radius r = a(1 − e·cos E) using each planet's real semi-major axis and eccentricity — Mercury's e = 0.206 visibly stretches its orbit, while Venus (e = 0.007) stays almost circular.
Orbital speed uses the vis-viva equation v = √(GM(2/r − 1/a)), so the readout shows a planet genuinely accelerating near perihelion and slowing near aphelion, exactly as Kepler's second law requires — not a constant angular rate.
Diameters and colors are the planets' real values (Mercury 4,879 km up to Jupiter 139,820 km); on-screen dot sizes are log-compressed so Mercury stays visible next to Jupiter, and the distance-scale toggle switches between a √AU-compressed true layout and an evenly-spaced diagram view — sizes are never to the same scale as distances on either setting, matching how every printed solar-system poster works.