Comparison of the model limb darkening as a function of μ = cos (θ), where θ ranges from 0° at the center of the star to 90° at the edge. We show limb darkening from four-parameter nonlinear limb-darkening coefficients obtained using ATLAS (solid lines) or PHOENIX (dashed lines) stellar atmosphere models, as well as the best-fit quadratic limb darkening obtained by a fit to our data (dotted lines). The color indicates the bandpass, including 3.6 μm (blue), 4.5 μm (green), and 8.0 μm (red) Spitzer bands. The gray shaded region indicates values of μ for which we have no direct observational constraints, as the planet does not cross this part of the star during its transit.