What is Effective Temperature?
The effective temperature of a planet is a theoretical temperature that a planetary body would have if it were a perfect black body in thermal equilibrium, radiating away exactly as much energy as it absorbs from its parent star. It is calculated without considering atmospheric effects, internal heat sources, or reflectivity.
Calculation Basis
This temperature is primarily derived from the planet's distance from its star and the star's luminosity. It assumes the planet absorbs all incident stellar radiation and re-emits it as a black body. The Stefan-Boltzmann law is central to its calculation, balancing the incoming stellar energy with the outgoing thermal radiation to find a global average.
A Practical Example: Earth's Effective Temperature
For Earth, the calculated effective temperature is approximately -18°C (255 K). This is significantly colder than Earth's actual average surface temperature of about 15°C (288 K). The difference highlights the crucial role of Earth's atmosphere and the greenhouse effect in trapping heat and making the planet habitable.
Importance and Applications
The effective temperature serves as a crucial baseline for understanding a planet's climate. By comparing this theoretical effective temperature to a planet's actual observed temperature, scientists can infer the presence and strength of an atmosphere, the greenhouse effect, or other internal heat sources, which are vital for assessing planetary habitability.