WASP-103b phase curve observations from HST/WFC3 (top) and Spitzer/IRAC (middle and bottom). For clarity, the data are phase-folded on the planet’s orbital period and binned in 30 uniformly spaced bins between 0 and 1 (corresponding to 0.8 hr). The left column shows the phase curves with systematic noise removed (black points) compared to the best-fit spherical harmonics model (colored lines). The error bars denote 1σ uncertainties (in some cases, the errors are smaller than the data points). We include the transits in the fit, but they are not displayed in this figure. The right-hand column shows the binned residuals for the best-fit light curve. The gray error bars in the upper right of the left panels correspond to 500 ppm, to illustrate the changing y-axis scale.