In comparison to the Earth, extraterrestrial environments possess quite different UV radiation regimes, both in terms of absolute flux and in terms of spectral quality (Horneck et al. 1984; Horneck 1993). For example, the moon has no atmosphere and thus its UV regimen is determined solely by the extraterrestrial spectrum. Mars, on the other hand, has an atmosphere that is one-hundredth the total atmospheric pressure of Earth and is composed of 95% CO2 (carbon dioxide). The surface UV flux is primarily determined by this atmospheric composition, and this flux is very different from that of the Earth. Planets around other stars will also have very different surface UV regimens, determined partly by their atmospheric composition but also by the fact that the spectral quality of light emitted by other stars can be very different from that of our own Sun.