Bessel measures stellar parallax
Bessel measures stellar parallax
Overview
In 1838 Friedrich Bessel announced the first reliable measurement of stellar parallax — an annual shift of about 0.3 arcseconds for the star 61 Cygni, observed with a heliometer at Königsberg. The result converted stellar distances from speculation into geometry and finally confirmed Earth's orbital motion predicted by heliocentrism. Parallax remains the fundamental first rung of the cosmic distance ladder.