T ⊕ can then be found: T ⊕ ⊕ 4 = R ⊙ ⊙ 2 T ⊙ ⊙ 4 4 a 0 2 T ⊕ ⊕ = T ⊙ ⊙ × × R ⊙ ⊙ 2 a 0 = 5780 K × × 6.957 × × 10 8 m 2 × × 1.495 978 707 × × 10 11 m ≈ ≈ 279 K where T ⊙ is the temperature of the Sun, R ⊙ the radius of the Sun, and a 0 is the distance between the Earth and the Sun. This gives an effective temperature of 6 °C on the surface of the Earth, assuming that it perfectly absorbs all emission falling on it and has no atmosphere.