Rossiter-McLaughlin Effect: Exoplanet Spin-Orbit Alignment (2D)

This simulator renders a rotating star as a face-on 2D disk Doppler-shaded by rigid rotation, then walks a transiting exoplanet across it along a chord tilted by the sky-projected spin-orbit angle λ. At every transit step the engine numerically integrates the local Doppler velocity, weighted by limb-darkened brightness, over every grid cell the planet currently occults — the same flux-weighted radial-velocity computation real spectrographs perform during an actual transit. The resulting anomalous RV curve is the real Rossiter-McLaughlin signal astronomers use to discover that many hot Jupiters orbit misaligned, polar, or even retrograde relative to their host star's rotation. Adjust the obliquity, impact parameter, planet size and stellar rotation speed and watch the RV curve — and its computed asymmetry statistic — reshape live, from the antisymmetric S-curve of an aligned system to the flattened, single-signed anomaly of a polar or retrograde orbit.