Nicolaus Copernicus is famous for his heliocentric theory, which states that the Sun, not the Earth, is the center of the solar system.

Here's a breakdown:

* Geocentric theory: The prevailing belief before Copernicus was that the Earth was the center of the universe, with all other celestial bodies revolving around it. This was known as the geocentric theory.

* Heliocentric theory: Copernicus proposed that the Earth and other planets revolve around the Sun. This was a radical idea that challenged the established scientific and religious views of the time.

Copernicus's heliocentric theory, though not fully accepted during his lifetime, revolutionized astronomy and laid the groundwork for future scientific discoveries.