Top: exoplanet transit geometry. Numerous spectral exposures were combined into ten average transit epochs, shown with the planet positions to scale (time increases left to right). Observations close to the limbs did not reach sufficient S/N for the later spectral reconstruction, and those two epochs are shown as open circles. Bottom: phase-folded HST light curve combining three planetary transits by Pont et al. (2007) with the flux at each epoch indicated by stars.