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How accurate were stellar parallax measurements made by the Hipparcos satellite?

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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.

The Hipparcos satellite, launched by the European Space Agency in 1989, significantly advanced the field of astrometry by measuring the positions and distances of approximately 100,000 stars.

Regarding the accuracy of its measurements, the satellite was able to compute individual stellar positions to within 0.001 arc second. This level of precision represented a 20-fold improvement over previous terrestrial estimates. By utilizing direct triangulation through observations of parallax from opposite sides of Earth’s orbit, Hipparcos provided a foundational dataset that helped refine the cosmic distance scale and calibrate the period-luminosity relationship of Cepheid variables.12