astronomy - conceptual, trigonometric parallax 1. The problem statement, all variables and given/known data To determine a star's trigonometric parallax, we need at least 3 measurements of its position relative to much more distanct objects. Explain why this is true. (What else could change its position on the sky?) 2. Relevant equations Note - this is for galactic astronomy. 3. The attempt at a solution Well, I understand what triangulation is.. take a measurement of the angle Earth at one end of its elliptical orbit and then six months alter at the other end, so you have the distance between, and with angles can figure out the distance to the star. But this question is asking relative to other distant objects, not Earth... so I'm not sure how to proceed thinking about it. What could change its position in the sky... light obscuration from dust, perhaps? I'd appreciate any guidance, thanks!