Which Renaissance astronomer first proposed a heliocentric model in his 1543 book?

The Renaissance astronomer who proposed the heliocentric model in his 1543 book was Nicolaus Copernicus. His major work, De revolutionibus orbium coelestium, argued that Earth moves around the Sun rather than occupying the stationary center of the cosmos.

Copernicus had developed the essential ideas decades before publication and circulated an outline known as the Commentariolus by about 1514. He delayed publishing his full theory, and De revolutionibus appeared in Nuremberg in 1543, the year of his death. The book marked a major turning point in the history of astronomy.

His model was not identical to the modern solar-system model. Copernicus retained circular orbits and epicycles, because he believed celestial motion should be uniform and geometrically perfect. His calculations were not immediately more accurate than the older Ptolemaic system, but the change in viewpoint was revolutionary.

Tycho Brahe, Johannes Kepler, and Galileo later played crucial roles in developing or supporting the new astronomy. Kepler replaced circular orbits with ellipses, while Galileo supplied telescopic observations that challenged geocentric ideas.