Use the sliders to move the Earth and change its distance from the sun. Note where the red star would appear in relation to the background stars.
Stellar parallax wasn't observed until 1838 when Friedrich Bessel first measured the effect using star 61 Cygi. It was known that it should be observable from Earth, provided by the Earth indeed moved in an orbit around the sun, but the effects were too small to be seen until telescope technology advanced. The geometry of the measurement is simple. Modern astronomical measurements still use parallax to determine the distance to stars.
Link to stand-alone sim: Here is a link to view the sim on its own, with no distractions.