Here's how it works:

1. Observation: Imagine holding your finger out in front of your face and closing one eye, then the other. Notice how your finger seems to shift position relative to the background. This is parallax.

2. Applying it to stars: Astronomers observe nearby stars from Earth at different points in our orbit around the Sun. The stars appear to shift slightly in position against the background of more distant stars. This shift is known as stellar parallax.

3. The bigger the shift, the closer the star: The amount of parallax is inversely proportional to the distance of the star. Stars that are closer to Earth show a greater shift than stars farther away.

4. Confirmation of heliocentric model: The fact that stars exhibit parallax provides strong evidence that the Earth is orbiting the Sun, rather than the Sun orbiting the Earth (the geocentric model).

Key points:

* Stellar parallax was first measured in 1838 by Friedrich Bessel, confirming the heliocentric model and allowing for the first accurate measurements of distances to stars.

* It is a fundamental tool in astronomy for determining the distances to nearby stars.

* The smaller the parallax, the farther away the star. Parallax is measured in arcseconds (1/3600 of a degree). A star with a parallax of 1 arcsecond is about 3.26 light-years away.

So, stellar parallax not only confirms the Earth's orbital motion around the Sun but also provides a key measurement for understanding the vast distances in our universe.