Celestia Forums

Well I've been trying to figure out stellar distances, and there are of course several ways to do this which I am aware of.

The parallax method usually involves taking some figure in mas (milliseconds of an arc) converting it to seconds of an arc and doing something like this 1 AU/parallax in arc seconds. To get the distance in parsecs.

The method I use is a bit more usefull for large distances, as parallax isn't all that effective beyond a certain distance from Sol. Anyway here is the equation I'm used to using:

10^((Mv-m-5)/-5)
In this equation Mv is the apparent magnitude and m is the absolute magnitude of any star as seen from Sol.

Now both equations return different, but similar results, for instance, in the RECONS data (http://www.chara.gsu.edu/RECONS/) gives Wolf 359 an apparent magnitude of 13.44 and an absolute magnitude of 16.55 With these figures plugged into the equation you find a distance of:

2.387811283 Parsecs or, 7.78808528 Light Years.

The parallax method yeilds a different result:

For Wolf 359 the parallax is 419.10 mas or .4191 Seconds of An arc yielding a distance of 2.386065378 parsecs or, 7.782390838 Light Years

The figures are different by .005694442 Light Years, or thats roughly 360.118676 AU, not much but significant.

I bring this up for several reasons, one I have added Wolf 359 to my Celestia program and I used the magnitude method. However, this method (or both methods in some ways) fall short of accurately placing companions to nearby stars. Such as Sirius B. Its possible to place the companions at the right locations, but in my case when I went to place Sirius B it ended up being .10 Light Years from Sirius A. So small deviations can result in big misplacements.

Are any of the rest of you running into this problem, and if so what is the running solution at this time?

You're not really entitled to more than a couple of decimal places in your distance measurement, using either method, since neither magnitudes nor parallaxes are measured to many significant digits.
So the only thing you can do is take the coordinates used by Celestia for Sirius, and add or subtract an offset for Sirius B. In my experience, this still requires a little trial-and-error for close companions.

Grant

they're going to give you different results cos the magnitude method is an approximation (assuming stellar type to get abs. mag. etc.) while the parallax method is only as good as your ability to measure angles between stars. and the previous poster is certainly right about the number of decimals you can reasonably calculate. magnitudes are generally 4 significant figures at best!