Light curves of a transit of WASP-80 b. Top panel: light curves obtained with the Danish Telescope (Bessel-I filter) and with GROND (Sloan-i′), highlighting the good match between the transit shapes in the two independent observations. The circles denoting the DK points have the same size as the corresponding error bars, which have been suppressed for clarity. Bottom panel: light curves obtained with GROND through four optical filters simultaneously, showing how the transit shape changes with wavelength.