Copernicus was a Polish ASTRONOMER who is best known for his heliocentric model of the universe, which proposed that the sun, rather than the Earth, was at the center of the universe. He was a contemporary of Galileo, another famous ASTRONOMER, and was influenced by the work of Ptolemy, an ancient Greek ASTRONOMER. Copernicus' name is also associated with a CRATER on the moon, named after him in recognition of his contributions to astronomy.