What idea did Nicolaus Copernicus put forth?

Nicolaus Copernicus put forth the idea of heliocentrism, which states that the sun is at the center of the solar system, and the planets, including Earth, orbit around it. This challenged the prevailing geocentric model of the universe, which held that Earth was the center of the universe and all celestial bodies revolved around it. The heliocentric model was later proven to be correct and revolutionized our understanding of cosmology.