Celestia Forums

I was fiddling around with a test star in Celestia, and I discovered that the habitable zone (AKA, the temperature read-out at an object with Earth's 0.30 albedo) is not tied to stellar luminosity/apparent magnitude, but rather the star's spectral type combined with stellar physical/visible radius. Why is that? Don't most sources (that I know of) say the HZ is based on luminosity, or am I misunderstanding it?

Bah, maybe because whether the habitable zone were inside the event horizon of a black hole, nobody would lives in there and nobody would see anything as well. If the luminosity were the basic criterium, how do you avoid such a case? (reductio ad absurdum)

Celestia's calculation of the black-body temperature of non-luminous objects (like planets) is known to be invalid for calculating habitable zones. It does not take into account the heating and cooling effects due to clouds and atmospheric composition, for example; not to mention other effects which are even less well understood. Since it also has other serious defects, my understanding is that there are plans to eliminate it entirely in the next major release of Celestia after v1.6.1.

Ah, ok.

Thanks for the clarification.

COROLLARIES:

- habitable zone = space-time.
- photon's spin = 0
- graviton's spin = 2

Bear in mind that Celestia makes various assumptions about stellar properties: relevant here are that the star's temperature and the bolometric correction (how to get from the brightness in visible light to the total luminosity) are solely dependent on the spectral type. This may give acceptable results over a large sample, but for individual cases this is going to give discrepancies. For example, the Sun has a lower temperature than a typical G2V star, this is a result of being more metal-rich than average.