Mine is most likely Radiative Transfer. The atmosphere has so many constituents that dictate how radiation in the shortwave penetrates the atmosphere and is either scattered, absorbed, or emitted, and how it affects the atmosphere in the longwave infrared. These equations manipulate Planck's function and have a ton of integrals. So interesting! But our class is so in-depth that we have taken leaps of faith from derivations that go as far back as Maxwell's Equations and how molecules rotate and induce electric fields. I never would have thought that today's supercomputers have a difficult time plotting absorption lines to fit global climate models. Some of these models take years to run! Well, enough of my little rant, I need to study for this class's final tomorrow morning. Share your tough college experiences!!!!