Yale professor Ron Smith builds a simple model of Earth's heat budget for his course The Atmosphere, the Ocean and Environmental Change. He starts from the assumption that incoming solar radiation must balance outgoing infrared radiation, then works through black body radiation using Wien's Law and the Stefan-Boltzmann Law to calculate an expected surface temperature. That bare model comes out colder than the real Earth, which sets up the lecture's main point: the atmosphere and its greenhouse effect account for the gap. Smith extends the calculation to other planets' energy budgets and closes by defining what actually makes a gas a greenhouse gas. Recorded in fall 2011 as lecture six of the Open Yale Courses series, the talk moves from basic radiation physics to planetary comparison in under an hour, with chapter breaks marking each stage of the derivation.