Exoplanet Radial-Velocity Wobble

A planet's gravity doesn't just hold it in orbit — it also tugs its host star into a small counter-orbit around their shared centre of mass. This simulator solves Kepler's equation for that stellar reflex motion in real time, renders the star and planet orbiting their barycenter in 3D, and colours the star blue or red as it approaches or recedes from an observer's line of sight — the same Doppler shift astronomers measure with a spectrograph. Tune the planet's mass, orbital period, eccentricity and inclination and watch the live radial-velocity curve and semi-amplitude K respond exactly as the physics dictates, including the sin i degeneracy that means spectroscopy alone can only ever measure a planet's minimum mass.