The theory that the planets revolve around the sun, known as the heliocentric model, was first proposed by the ancient Greek astronomer Aristarchus of Samos in the 3rd century BC.

However, his theory was largely rejected at the time in favor of the geocentric model, which held that the Earth was the center of the universe. It wasn't until the 16th century that Nicolaus Copernicus revived the heliocentric model with his book "De Revolutionibus Orbium Coelestium" (On the Revolutions of the Heavenly Spheres).

While Copernicus is often credited with discovering the heliocentric model, it's important to recognize that Aristarchus was the first to propose it.