"OG"  wrote in message news:674f69F2neekkU1@mid.individual.net...
>
> What do you have so far ?
>
> Stellar parallax is the angle subtended by the radius of the Earth's orbit
> at the star.
> http://en.wikipedia.org/wiki/Parallax#Stellar_parallax
>
> Radius of Earth's orbit is appx 150,000,000 km
>
> The distance to the star is
> 150,000,000 / sin (parallax)
>
> Which gives you a measurement in km
>
> You then divide by the number of km in a light year.
>

Thanks for the help.  From that article, it appears that a simplified
equation for earth-orbit parallax is

    parallax (in arcseconds) = 1 / distance (in parsecs)

Am I reading that correctly?