This DigiKit for upper-division physics or astronomy explores factors that influence average surface temperature of a planet. As students will discover, distance from a host star is only one factor. Planetary surface temperature is also affected by albedo, the ratio of incident light reflected by the planet. Greenhouse gas concentrations also play a role, as well as nuclear fusion processes and brightness of the planet's host star. The keystone of the DigiKit, the Habitable Zone Planets Lecture Tutorial, integrates mathematics as students calculate total power absorbed and radiated per unit squared in spherical objects, calculate albedo, explore the Proton-Proton Chain, and offer "solutions" to the Faint Young Sun Paradox. The tutorial is supplemented with interactive simulations, animations, background information, and a full section designed for use by aspiring high school physics and astronomy teachers.