where T E is the temperature of the planet. This temperature, calculated for the case of the planet acting as a black body by setting P a b s = P e m t b b , is known as the effective temperature. The actual temperature of the planet will likely be different, depending on its surface and atmospheric properties. Ignoring the atmosphere and greenhouse effect, the planet, since it is at a much lower temperature than the Sun, emits mostly in the infrared (IR) portion of the spectrum. In this frequency range, it emits ϵ ϵ ¯ ¯ of the radiation that a black body would emit where ϵ ϵ ¯ ¯ is the average emissivity in the IR range. The power emitted by the planet is then: