What star was used for the first successful measurement of stellar parallax? 61 Cygni was the star used for the first successful measurement of stellar parallax.
Friedrich Bessel announced the measurement in 1838 after observing the 61 Cygni system with a heliometer at Königsberg. By comparing its position at different points in Earth’s orbit, he detected the tiny apparent displacement caused by the observer’s changing viewpoint. This geometric effect, called parallax, allowed him to estimate the star’s distance.
61 Cygni was a strong target because it has unusually large proper motion, meaning it appears to move noticeably against more distant background stars. Giuseppe Piazzi had drawn attention to that motion in the early nineteenth century and suggested the system as a promising parallax candidate. The system is actually a widely separated binary, designated 61 Cygni A and B.
Bessel’s original distance estimate was about 10.4 light-years; modern measurements put the system at roughly 11.4 light-years. A common mix-up is to name Alpha Centauri, which is closer and has a larger parallax, but its successful measurement came later. 61 Cygni is remembered as the first star whose stellar parallax was reliably measured.