While it's difficult to pinpoint the absolute first person to hold this belief with certainty, Nicolaus Copernicus is widely recognized as the first astronomer to propose and publicly defend the heliocentric model of the solar system.

Here's why:

* Copernicus's Heliocentric Model: In his groundbreaking book *De Revolutionibus Orbium Coelestium* (On the Revolutions of the Heavenly Spheres), published in 1543, Copernicus laid out a detailed mathematical and observational argument for the Sun being the center of the solar system, with all planets, including Earth, orbiting it.

* Previous Ideas: While Copernicus was the first to publish a comprehensive and well-argued heliocentric model, there were earlier thinkers who had hinted at similar ideas. For example, Aristarchus of Samos (c. 310-230 BC) is known to have proposed a heliocentric model centuries before Copernicus, but his work was largely ignored.

* Impact of Copernicus's Work: Copernicus's work, despite facing initial resistance, had a profound impact on the scientific world. It laid the groundwork for the eventual acceptance of the heliocentric model and revolutionized our understanding of the universe.

It's important to note that the acceptance of the heliocentric model was a gradual process. Even after Copernicus, many astronomers and thinkers still held on to the geocentric model. It wasn't until the work of Galileo Galilei and Johannes Kepler that the heliocentric model gained wider acceptance.