The Sun does not shine at GeV energies on its own power, but because cosmic rays interact with its matter and light. By observing and modeling these interactions in and near the Sun, one may learn about cosmic-ray propagation in the inner heliosphere and in the solar atmosphere. In this talk, I will present new observations of the Sun with the Fermi/LAT instrument which show that the Sun is a luminous source of E > 10 GeV gamma rays. These observations suggest that all attempts so far to model the cosmic-ray interactions with the Sun are incomplete, and highlight our ongoing efforts to reconcile these observations with our models. Finally, I will discuss the implications of this work for the Sun as a ~ GeV - TeV signal for gamma-ray and neutrino observatories.
