It's a bit tricky to pinpoint one person who "realized" that the planets go around the sun. It was a process of discovery and acceptance that took centuries, involving many individuals.

Here's a breakdown:

* Ancient Greek philosophers: Some ancient Greeks, like Aristarchus of Samos (310-230 BC), proposed a heliocentric model (sun-centered) but lacked strong evidence and the model wasn't widely accepted.

* Nicolaus Copernicus (1473-1543): Copernicus revived the heliocentric model in his book "De Revolutionibus Orbium Coelestium" (On the Revolutions of the Heavenly Spheres). He provided mathematical evidence and challenged the prevailing geocentric model (Earth-centered).

* Tycho Brahe (1546-1601): While Tycho Brahe himself believed in a hybrid model, he made extremely accurate astronomical observations that later helped prove the heliocentric model.

* Johannes Kepler (1571-1630): Kepler used Tycho's data to develop his three laws of planetary motion, which mathematically explained the elliptical orbits of planets around the sun.

* Galileo Galilei (1564-1642): Galileo's observations with the telescope provided crucial evidence for the heliocentric model. He saw phases of Venus, which could only be explained if it orbited the sun.

So, while Copernicus is often credited with the heliocentric model, it was a cumulative effort of many scientists over centuries who challenged the prevailing view and provided more and more evidence.