Stellar parallax is the effect of parallax on distant stars in astronomy. It is parallax on an interstellar scale, and it can be used to determine the distance of Earth to another star directly with accurate astrometry. It was the subject of much debate in astronomy for hundreds of years, but was so difficult it was only achieved for a few of the nearest stars in the early 19th century. Even in the 21st century, stars with parallax measurements are relatively close on a galactic scale, as most distance measurements are calculated by red-shift or other methods.
The parallax is usually created by the different orbital positions of the Earth, which causes nearby stars to appear to move relative to more distant stars. By observing parallax, measuring angles and using geometry, one can determine the distance to various objects in space, typically stars, although other objects in space could be used.
Because other stars are far away, the angle for measurement is small and the skinny triangle approximation can be applied, the distance to an object (measured in parsecs) is the reciprocal of the parallax (measured in arcseconds): For example, the distance to Proxima Centauri is 1/0.7687=1.3009 parsecs (4.243 ly). The first successful measurement of stellar parallax was made by Friedrich Bessel in 1838 for the star 61 Cygni using a Fraunhofer heliometer at Königsberg Observatory.
Read more about Stellar Parallax: Early Theory and Attempts, 19th and 20th Centuries, Space Astrometry For Parallax, Other Baselines, Other Parallax in Astronomy