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How does a star’s distance change when its parallax angle becomes smaller?

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Diagram illustrating how astronomers calculate the distance to a star using parallax: Earth is shown in two positions on opposite sides of its orbit around the Sun, with lines extending to a nearby star X and further to distant background stars. The apparent shift in star X's position, measured as angle A, is used to determine its distance, with the baseline labeled as 186,000,000 miles. — Parallax Calculating stellar distances.

When a star’s parallax angle becomes smaller, the distance to that star increases.

This relationship exists because parallax is inversely proportional to distance. Astronomers use the radius of Earth’s orbit as a baseline to form a triangle with the star; as the star moves further away, the angle formed by this baseline at the star's position becomes increasingly narrow.12

For example, a star with a parallax of 1 arc second is located at a distance of 1 parsec (approximately 3.26 light-years), whereas a star with a smaller parallax of 0.1 arc seconds is located at a distance of 10 parsecs. Because these angles are extremely small, measuring them requires high-precision astronomy to accurately determine the distances of stars.12