Measuring the distance to stars using parallax

[alemsalem]

how can you use the angle to determine the distance if you don't know the motion of the star itself.
is it by observing the star from the same point in two different years and then subtracting off this effect?

 

[russ_watters]

Motion? That doesn't have anything to do with the distance. The difference in position provides you an angle and the diameter of Earth's orbit a measuring stick.

Try drawing a diagram.

 

[Drakkith]

Most stars do not move significantly over the course of 6 - 12 months. For those that do you can simply figure out the proper motion and correct for it to find the parallax.

 

[Chronos]

You are correct, asalem. The proper motion component is derived from multiple parallax measurements. It is, however, vanishingly small for most stars. See http://csep10.phys.utk.edu/astr162/lect/motion/proper.html.