Which scientists described the universe and what were their theories?

Claudius Ptolemy and Nicolaus Copernicus both described the universe.

Ptolemy, a Greek astronomer, wrote a book that combined all knowledge of astronomy that he could find. He expanded ancient theories with careful mathematical calculations in what was called the Ptolemaic Theory. Ptolemy thought the Earth was the center of the Universe and that the sun and other planets revolved around Earth. Although this theory was incorrect as we now know, it predicted motions of the planets better than any other theory at the time did.

Copernicus, a Polish astronomer, published a new theory that would eventually revolutionize astronomy. Copernicus thought the Sun was the center of the universe, and all the planets (including Earth) orbit the sun. Although Copernicus correctly thought that the planets orbit the sun, his theory did not replace Ptolemaic theory immediately. When Copernicus's theory was accepted, major changes in science and society called the Copernican revolution took place.