Geometry of the 5 October 2017 stellar occultation by Triton, as seen in the sky plane. The J2000 celestial north (N) and east (E) directions and the scale are indicated in the upper right corner. Triton’s radius is fixed at R_T = 1353 km, and the grey arrow near the equator shows the direction of rotation of the satellite. The (Neptune-facing) prime meridian is drawn as a thicker line compared to the other meridians, and the south pole is marked by the label S. The inclined lines are the trajectories of the star relative to Triton (or ‘occultation chords’) as observed from various stations, with the black arrow indicating the direction of motion. We gathered a total of 90 occultation light curves, 52 of which (corresponding to the blue colour, as in Fig. 4) had sufficient S/N to be included in a global atmospheric fit; the remaining 38 (red colour) with lower S/N were not included in the fit.