The famous astronomer who formulated the heliocentric model of the solar system was Nicolaus Copernicus. His revolutionary theory proposed that the Sun, rather than the Earth, is at the center of the universe, fundamentally changing the understanding of our solar system. Published in his work "De revolutionibus orbium coelestium," Copernicus's model laid the foundation for modern astronomy, challenging the long-held geocentric views and paving the way for future astronomers like Galileo and Kepler.