The heliocentric theory is the astronomical model that places the Sun at the center of the solar system, with the Earth and other planets orbiting around it. This concept was first proposed by the ancient Greek philosopher Aristarchus of Samos but gained prominence in the 16th century through the work of Nicolaus Copernicus. Before the heliocentric theory, the prevailing belief was the geocentric model, which positioned the Earth at the center of the universe. The acceptance of the heliocentric theory marked a significant shift in scientific thought, leading to advancements in astronomy and our understanding of the cosmos.