Copernicus was Galileo Galilei's friend. [No. Copernicus died in 1543, before Galileo was born (1564).] Copernicus proved that the Sun, not the Earth, is in the center of the solar system, the planets, including the Earth, revolving around the Sun.
Copernicus was in 1543, a polish astronomer named Nicolaus Copernicus. Copernicus's theory - The sun is at the center of the Universe. Galileo Galilei was in 1609, Galileo became the first person to use a telescope to observe celestial bodies.