Graphic of atmospheric parts probed during the separated parts of mid-transit and egress data in a polar planetary view. The host star is indicated on the left, with the observer as a small VLT UT on the right. WASP-121 b is shown in the middle with its obscure planet disc as the smaller circle and the atmosphere extension as the larger circle. The grey areas indicate the light from the host star crossing the exo-planet atmosphere over each limb in the line of sight. The depiction of WASP-121 b at the bottom is shown roughly at mid-transit, where the terminator (short dashed line) is orthogonal to the line of sight. At the top it is shown at a moment in time during the egress part of the dataset, when the planet has rotated and shows a different opening angle than during mid-transit, with different parts of the atmosphere probed across both limbs. The opening angle is indicated by the longer, dashed lines starting at the centre of the host star. The graphic is not to scale.