Celestia Forums

Well after checking out the stars i noticed something rather odd,star A is at 18 sol radius and B at 1.2 sol radius althogh all reference i can find state that A is 12.2 sol radius and B is 9.2 sol radius (though temperatures seem ok), even in celestia on looks exagerated ove the other.

is this by design? or some mistake that was overlooked?

zhar2 wrote:Well after checking out the stars i noticed something rather odd,star A is at 18 sol radius and B at 1.2 sol radius althogh all reference i can find state that A is 12.2 sol radius and B is 9.2 sol radius (though temperatures seem ok), even in celestia on looks exagerated ove the other.

is this by design? or some mistake that was overlooked?

What Celestia version!?
What data file?

Fridger

Its celestia 1.5.1 (the latest donload available from main page), i really dont know wich file but i imagine its stars.dat (in celestia A is at 18 sol rad and B is at 1.2).

zhar2 wrote:Its celestia 1.5.1 (the latest donload available from main page), i really dont know wich file but i imagine its stars.dat (in celestia A is at 18 sol rad and B is at 1.2).

The calculation of star radii in Celestia is VERY rough. The Stefan-Boltzmann law is used to estimate the radius of a star from surface temperature and luminosity. Such simplistic estimates can always encounter pretty large errors. As of Celestia 1.6.x, Andrew has also implemented a limited set of measurement-based (CHARM2) star radii, but for ALF Aur there are no new data as far as I could tell.

The measured orbital data about the ALF Aur system are specified in my spectbins.stc data file for spectroscopic binaries. The radii are however estimated in the core file 'star.cpp'.
Since these values are calculated from a single formula, there is nothing we can do about it, except improving that formula eventually, which is not easy

Since the star radius is a rather uncertain, calculated quantity in Celestia, it is only displayed in the verbose (non-default) display... People should understand that these values can at best serve as order of magnitude estimates.

Fridger

Ah well, shame it cant be changed but now i understant the how the error arrised (yes i would imagine that improving the formula would be extremely difficult), anyway as a celestia user i just felt compelled to report it

Also see the paper published in this thread I posted here a few days ago.

ajtribick wrote:Also see the paper published in this thread I posted here a few days ago.

I understand it roughly, but the details are over my head but i like to get to understand stuff so i will look at it closely and research anything i dont understand.