Astronomers have several tools for finding the distances between Earth and distant celestial bodies. One of these tools is parallax measurement. Parallax is a change in viewing angle (i.e., the direction towards which the viewer looks) of a distant object due to a change in position of the viewer. Astronomers use the Earth’s movement around the sun to measure the parallax of distant objects. In this demonstration, you can see how the precision with which we can measure the viewing angle of a celestial body (ΔΘ) and the distance of the object (R, in pixels) work together to affect the uncertainty in our distance measurement (ΔR). Try dragging the distant star around and note how the uncertainty compounds as the star becomes farther and farther from the viewer.