1. The problem statement, all variables and given/known data At lunch, the Sun's thermal energy incident on the surface of the Earth is 1.4 kW/m^2. Given the radius of the Sun, R, distance from Earth, r, and treating the Sun like a perfect black body, calculate the total intensity of its radiation and determine its temperature. 2. Relevant equations 3. The attempt at a solution I have no idea which formula to actually use. I've attempted applying Rayleigh-Jeans and Planck's derivation of it but I simply cannot see how R and r come into play. Perhaps as integer wavelength conditions?