Hello, It looks like Stefan Boltzmann Law can be used for a lot of different purposes: to calculate the temperature of stars, sun, temperature of the Earth's sky, temperature of particular surface, wall, the radiation emitted by the body by knowing its temperature, and so on. What confuses me is: in all these modern examples of the use of Stefan Boltzmann Law, there is an initial assumption that the black or gray body which emits the energy is approximated to be a sphere? Is this correct or not? Is it crucial for the Stefan Boltzmann Law, that the body in question is a sphere, so that it equally emits the energy in all directions? Thank you for the reply.