Transmission spectroscopy of exoplanets is a tool to characterize rocky planets and explore their habitability .
Using the Earth itself as a proxy , we model the atmospheric cross section as a function of wavelength , and show the effect of each atmospheric species , Rayleigh scattering and refraction from 115 to 1000 nm .
Clouds do not significantly affect this picture because refraction prevents the lowest 12.75 km of the atmosphere , in a transiting geometry for an Earth-Sun analog , to be sampled by a distant observer .
We calculate the effective planetary radius for the primary eclipse spectrum of an Earth-like exoplanet around a Sun-like star .
Below 200 nm , ultraviolet ( UV ) O _ { 2 } absorption increases the effective planetary radius by about 180 km , versus 27 km at 760.3 nm , and 14 km in the near-infrared ( NIR ) due predominantly to refraction .
This translates into a 2.6 % change in effective planetary radius over the UV-NIR wavelength range , showing that the ultraviolet is an interesting wavelength range for future space missions .