black body temperature
The temperature that the surface of a body (such as a planet, like the Earth) would be if it were not warmed by its own atmosphere. It can be calculated using the Stefan–Boltzmann equation. The black body temperature of the Earth is -23°C, but the actual surface temperature is about 15°C. The difference (38°C) is the amount by which the planet is warmed by the absorption of radiation within its atmosphere, by the natural greenhouse effect.