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There are a few bright comets approaching this year. I would like to enter them as accurately as possible into Stellarium, but I am not sure what to do with the sidereal_period and radius when they are unknown.
For example, JPL (http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=ison;orb=0;cov=0;log=0;cad=0#phys_par) shows lots of information for Comet ISON C/2012 S1, but it doesn't have the radius or the sidereal_period.
So what should be entered for the radius and sidereal_period when it is unknown?
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Many comets have more or less the same radius and we can use it value as mean radius for comets. Sidereal period can be easy calculated for bodies with elliptical orbits.
P.S. Where you found sidereal period for C/2012 S1?
<< Where you found sidereal period for C/2012 S1? >>
I haven't found any. That is why I am asking. So what should be entered when you don't know what it is? Or should that parameter be skipped and not entered?
Hyperbolic (like C/2012 S1) and parabolic comets don't have sidereal period. ;)
So should I remove the sidereal_period parameter for C/2012 S1?
Yes, this value impossible physical for hyperbolic comets.
<< Many comets have more or less the same radius and we can use it value as mean radius for comets. >>
What is that value?
Most cometary nuclei are no more than about 10 miles (16 kilometers) across.
We set minimal radius in 1 kilometer for bodies with unknown size (for guarantee and simplification calculations).