Here's why:

* The Earth's Orbit: As the Earth revolves around the Sun, our vantage point in space changes slightly.

* Apparent Shift: Imagine holding a finger in front of your face and closing one eye, then the other. Your finger appears to shift position against the background. This is the same principle that applies to stars.

* Parallax: Due to the Earth's orbital motion, a nearby star appears to shift its position slightly against the background of distant stars throughout the year. This apparent shift is called parallax.

* Measuring Distance: The larger the parallax angle, the closer the star. This relationship allows astronomers to calculate the distance to nearby stars.

Let me know if you'd like a more detailed explanation of how parallax is measured!