The theory of heliocentrism was proposed by Nicolaus Copernicus in the 16th century. In his groundbreaking work "De revolutionibus orbium coelestium," Copernicus argued that the Sun, rather than the Earth, was the center of the universe, and that the planets, including Earth, revolved around it. This revolutionary idea challenged the long-established Ptolemaic model, which positioned the Earth at the center of the universe. Copernicus's heliocentric theory set the stage for future scientific inquiry, influencing figures such as Galileo and Kepler, and marking a significant shift in humanity’s understanding of its place in the cosmos.