Celestia Forums

This may or may not be something anyone can fix, but, while I was inputing the data for some smallish stars, like Wolf 359, I manage to get the distances and magnitudes right, but, what invariably will happen is Celestia will assign them some ungodly small size like .02 Sol or .03 Sol (like the size applied to a white dwarf). I imagine this has to do with how Celestia determines Radii, but I thought I'd let you guys know.

I think this error arises from the way Celestia calculates stellar radii.
Since luminosity per unit area scales with the fourth power of the temperature, Celestia uses the following equation to derive a radius once it knows a star's temperature and luminosity:

radius[in solar radii] = sqrt(luminosity)*(temp sun/temp star)^2

For this equation to work, the luminosity used must be the bolometric luminosity, the total energy output of the star. But the absolute magnitudes used in Celestia are visual magnitudes - and at the cool end of the stellar classification, visual mag can be about 4 magnitudes less than bolometric. I'm guessing this hasn't been taken into account when deriving luminosities, making the calculated radius in your red dwarf ~6 times smaller than it should be.

Since the code is already using a look-up table to return the stellar temperature for a given spectral class, it should be possible to use another lookup to return a bolometric correction, too, when deriving luminosity from visual magnitude.

Grant