Equilibrium temperature

A planet's equilibrium temperature is the balance point it reaches when the heat it soaks up from its star equals the heat it radiates back to space. It depends on how bright the star is and how far away the planet orbits, and it deliberately ignores any atmosphere. It is the honest starting number: the temperature of a bare rock sitting in that much sunlight.

Real worlds can run much hotter. Earth's equilibrium temperature is well below freezing; our atmosphere's greenhouse effect is what lifts the surface to a livable average. Venus is the extreme case, hundreds of degrees hotter than its equilibrium value. gravityfinder uses equilibrium temperature for every exoplanet because it can be worked out the same way for all of them, and it is always labelled as such. Only our own solar system carries a measured mean surface temperature, and the site shows the two side by side, never one in place of the other.