Schematic demonstrating how the smearing effect arises due to increased exposure length. Using an illustration of exoplanet WASP-127 b and its host star (to scale) as an example, consider the target’s transit time t_transit = 4.35 h = 15 660 s. A shorter exposure time of t_exp = 500 s (left) covers approx. 3% of the total transit time, versus a longer exposure time of t_exp = 1000 s (right) which covers approx. 6%. In this schematic, the location of the planet at the beginning and end of an exposure of length t_exp is shown by the shaded, dotted regions. The relative distance between these regions illustrates how much the target moves across a single exposure of the given time. This movement is greater for the longer exposure and thus will give rise to a larger smearing effect.