Example of transmittance maps at two different times of a simulation of K2-18b (Charnay et al. 2021) at a wavelength of 0.6 μm from the observer’s point of view. The atmosphere is transparent when the transmittance is equal to 1, and it is opaque when it is equal to 0. The absence of clouds is visible on the right side, which corresponds to the west limb. The atmosphere scale height has been multiplied by 10 for visual reasons. The altitude is in Mm, i.e., thousands of km.