The impact of limb-darkening polynomial order on transit light curves. We first simulated a transit of a Kepler-167 e-sized planet across a Kepler-167-like star, using a 10th-order polynomial approximation to the stellar intensity profile generated using the Kurucz stellar grid. We then simulated four other transits using successively lower polynomial orders for the stellar intensity approximation, and differenced the resulting transits with the fiducial one. The differenced curves, shown above for the 2nd–10th order, 4th–10th order, etc., reveal that low-order approximations impart residuals of tens of ppm over the course of the transit.