Who was the first astronomer to measure stellar parallax?

Who was the first astronomer to measure stellar parallax? Friedrich Bessel was the first astronomer to make a reliable measurement of stellar parallax.

In 1838, the German astronomer Friedrich Wilhelm Bessel used a Fraunhofer heliometer at the Königsberg Observatory to measure the apparent shift of 61 Cygni as Earth moved around the Sun. His result gave the star a parallax of about 0.314 arcseconds and placed it roughly 10.3 light-years away.

The word “reliable” matters. Earlier astronomers, including James Bradley, Giuseppe Piazzi, and William Herschel, studied stellar positions or attempted distance measurements, but their observations did not produce a dependable stellar-parallax result. Bradley’s 1728 discovery of stellar aberration was especially important evidence for Earth’s motion, but it was not a measurement of parallax.

Bessel’s achievement helped settle a long-standing challenge to heliocentrism: if Earth orbits the Sun, nearby stars should appear to shift against distant ones. The shift was tiny because the stars are extraordinarily far away. Bessel’s work therefore provided both a distance scale for astronomy and direct observational support for the Copernican model.