The parallax method is a technique used in astronomy to measure the distance to nearby stars. It takes advantage of the apparent shift or displacement of a star's position when observed from different points in Earth's orbit around the Sun.

The basic principle of the parallax method is trigonometric. When observing a nearby star from two different positions on Earth's orbit, the star appears to shift its position relative to more distant background stars. This shift is known as parallax. By measuring the angle of the parallax shift, astronomers can calculate the distance to the star.

The parallax angle, denoted as p, is defined as half the angle formed by the line of sight to the star from two different positions in Earth's orbit. The distance to the star, d, is related to the parallax angle by the equation:

d = 1 / p

The parallax method is limited to relatively close stars within a few hundred parsecs (a parsec is approximately 3.26 light-years). For stars that are farther away, the parallax angle becomes too small to measure accurately.