Everything is Moving

Another challenge is the fact that the star’s position you are measuring, the Sun and Solar System, and these background stars are also moving. The way to overcome this issue is to make more than two measurements and to take into account all of the motions – the Solar System and background reference stars.

Image of theStellar Parallax diagram. The apparent motion of a near by star is a small ellipse in the sky relative to background stars over the period of a year. The angle representing major axis radius of the elliptical path is the parallax angle. The minor axis radius angle is simply related to the direction of the star relative to the earth's orbital axis. Stars near the north and south poles will make perfect circles, while stars near the ecliptic will make flat ellipses.
Public Domain | Image courtesy of Wikimedia Author: Booyabazooka