Planetary equilibrium temperature

The equilibrium temperature indicates the temperature which is established after a sufficiently long time in a system by itself. In astronomy, the equilibrium temperatures of gas clouds and planet surfaces are important.

Equilibrium temperature of a planet's surface

Under the assumptions that

Applies with the designations

For the solar energy absorbed per second, the expression

Here, the luminosity of the Sun is spread over the whole sphere with radius, with this density, but does all the planet's surface energy. From the theoretical energy lost by reflection. The radiated energy per second

The equation for the radiated energy follows from the product and the surface temperature to the fourth power with the proportionality constant.

The equilibrium condition results

For the Earth, this results with the value that is with in, but observed. This higher temperature due to the greenhouse effect. This is particularly strong on Venus, where the calculated temperature, the measured value but with lies. A reverse effect is found in Mars, which has a much thinner atmosphere than the two mentioned above: There, the calculated temperature is of slightly higher than the actually observed.