Stellar parallax is the apparent shift in position of a nearby star against the background of more distant stars as observed from different points in Earth's orbit around the Sun. This effect occurs because as Earth moves, the angle from which we view the star changes, allowing us to measure its distance. Astronomers use stellar parallax to calculate the distance to stars. By measuring the angle of this shift, known as the parallax angle, and applying simple trigonometry, they can determine how far away the star is. This method is crucial for understanding the scale of the universe.