How does parallax work if the universe itself is expanding?

I mean, parallax assumes that the sun is stationary with respect to the nearby star. a href="http://upload.wikimedia.org/wikipedia/commons/e/e3/Stellarparallax2.svg" rel="nofollow"http://upload.wikimedia.org/wikipedia/co…/a But since the universe is expanding, the sun's position with respect to the star today is different than its position 6 months from now. How do you compensate that? How do we even know how and where the sun moves with respect to the star?