When a planet crosses its star it blocks a fraction of the light: transit depth ΔF/F = (R_P/R_S)². Kepler and TESS have discovered 5,000+ exoplanets this way. Impact parameter b = a·cos(i)/R_S controls whether the transit is central or grazing. From depth, duration and period the planet radius, orbital distance and — combined with radial velocity — mass are derived. The simulator draws the real overlap geometry per frame.
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