Spectrum of WASP-121b at different orbital phases, α = 0° being the secondary eclipse. Emission features are expected for − 120° < α < 60° whereas absorption features are seen for α < −120° and α > 60°. The spectra at phases − 120° and − 60° are well represented by an area weighted sum of the dayside and the nightside spectrum (dotted line) but the 120° and 60° spectra are not.