Similarly we can calculate the effective temperature of the Earth T ⊕ by equating the energy received from the Sun and the energy radiated by the Earth, under the black-body approximation (Earth's own production of energy being small enough to be negligible). The luminosity of the Sun, L ⊙, is given by: L ⊙ ⊙ = 4 π π R ⊙ ⊙ 2 σ σ T ⊙ ⊙ 4