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 theory was first proposed by the ancient Greek philosopher Aristarchus of Samos but gained prominence in the 16th century through the work of Nicolaus Copernicus. The Heliocentric Theory challenged the earlier Geocentric Theory, which held that the Earth was the center of the universe. Copernicus's ideas laid the groundwork for modern astronomy, influencing later scientists like Galileo Galilei and Johannes Kepler, who provided further evidence and refinement of the model.