Celestia Forums

Why the temperature range of the planet venus is bettwen 229 kelvin - 230 kelvin and the earth range is 256 to 261?

Sorry for my bad english!!

Temperature calculation is done by working out the balance of energy as follows:

The planet receives a certain amount of radiation from the star. Some of this is reflected into space (parameter that controls this is the albedo). The remainder is absorbed by the planet. The planet reradiates thermal radiation. Equating the energy absorbed to the energy reradiated, you then find the temperature. This value is the value displayed by Celestia. Reason the Venus temperature is lower is that the reflective cloud cover more than compensates for the larger amount of radiation received.

Celestia's calculation is dubious because it uses the same value for both the visual albedo and the Bond albedo. It also doesn't take into account the non-blackbody properties of a planetary atmosphere that leads to greenhouse heating, which is a fairly significant effect on some planets.

(Probably would be better to remove Celestia's temperature value for planets altogether)

Have a question about temperature and thought I'd search for similar threads instead of making a new topic.

I was wondering about the accuracy of the temperatures as I am building a fictional habitable world around a M9III giant with an AbsMag of 4.07. This is a world I'm using as a setting in a series of short stories that is cloud covered with perpetual rainfall. With an albedo of 0.85, a SMA of 20.58 AU gives me 258 K, and with an albedo of 0.45, 357 K. To keep my temperature around 257 K at an albedo of 0.45 I need a SMA of 39.7 AU. Since other processes are involved in determining the surface temperature can the Celestia temperature results be ignored in the scope of creating somewhat hard science fiction? I would prefer the 20 AU orbit with a 0.45 albedo, but the most realistic scene wins.

Celestia does not take into account atmospheric greenhouse effects. It seems likely that the temperature display will be removed in the next major release.

Exactly how the atmosphere, solar spectrum and planetary water affect planetary temperature is a topic of ongoing research that I know little about. I suspect you could find appropriate research papers as easily as I could.

Thanks Selden. That's all I needed to know.