The apparent movement of a star used to measure its distance from Earth is called parallax.

Here's how it works:

* The Concept: Imagine holding your finger in front of your face and closing one eye, then the other. Your finger appears to shift position relative to the background. This is parallax.

* Stars and Parallax: As the Earth orbits the Sun, our vantage point changes. This causes nearby stars to appear to shift their position very slightly against the background of more distant stars.

* Measuring Distance: The amount of this apparent shift is directly related to the star's distance. The greater the shift, the closer the star.

So, by measuring the parallax angle of a star, astronomers can calculate its distance from Earth.