Relation between distance d and paralax plx is:
$$d (pc) = 1 / plx(arc)$$
When I want to express plx in mas, will it be
$$d (pc) = 1/[plx(mas)*1000]$$
or $$d (pc) = 1000/plx(mas)$$
Thank you very much
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Sign up to join this communityTo convert mas to arcseconds, you divide by 1000, so the proper equation would be: $$ d(pc)=\frac{1}{plx(mas)/1000} $$
Which can be rewritten as your second equation: $$ d(pc)=\frac{1000}{plx(mas)} $$
I'll add that the above is an approximation algorithm, the true relation between distance and parallax is:
$$ d = \frac{1au}{\tan \theta} $$ d = Distance in AU
$\theta $ = Angle in degrees ($\theta = p/3600$)
On any modern processor, there is little need to ever use the approximation.