Which 1728 discovery by James Bradley gave direct evidence for Earth's motion around the Sun?

James Bradley’s 1728 discovery that gave direct evidence for Earth’s motion around the Sun was the aberration of light.

Bradley and Samuel Molyneux were trying to detect stellar parallax, the apparent annual shift expected as Earth moves around the Sun. Instead, observations of Gamma Draconis and other stars revealed a different yearly displacement. Bradley recognized that the pattern could be explained by Earth’s changing orbital velocity combined with light’s finite speed.

The apparent stellar shift reaches roughly 20 arcseconds in amplitude and is not the same pattern expected from parallax. Because the effect tracks Earth’s orbital motion, it provided strong observational support for heliocentrism. Bradley developed the explanation in 1728, and it was presented to the Royal Society in January 1729.

Aberration is often confused with stellar parallax, but the two arise differently. Parallax is a geometric viewing effect caused by changing observer position; aberration is an apparent directional shift caused by the motion of the observer and the finite speed of light.