This is a very simplified conceptual drawing of a planet with atmosphere and lumped albedo, a partially reflecting layer in a thermal flux. (semi-silvered mirror if you like)
Why is the planet at the same temperature for any sane albedo?
On entry the flux is attenuated by some proportion of the flux not making it through to the planet: therefore the flux value reaching the planet is smaller.
If the flux then radiated by the planet was not attenuated by albedo on the way out, where normally some returns to the planet, this is equivalent to perhaps Earth in an orbit beyond Mars and would be very cold. Albedo in and out must be very similar because that is what see for real.
Each time forward radiation from the surface meets the partial reflecting layer some gets through, some is returned after a delay, no time travel, no perpetual motion.
The albedo value cancels.
The albedo value for the dark side of a planet is poorly known, no daylight.
Please note that I know there are many details, problems and connundrums which I could show in many pages, such as the frequency response of the various components, where the effect is a product of terms. Also note the flux source, such as our Sun is hotter than the planet at all frequencies/wavelengths, right down to long radio waves.
Conceptually is the above correct? (this has nothing to do with the discussions over gas pressure, a different issue)
Post by Tim Channon, co-moderator.