Copernicus Copernicus' work on planetary motion stood an a very high mathematical level for his times. His theory explained how all the celestial bodies move around the Sun. It took Nicolaus 30 years of mathematical research to form a theory about planetary motion. The three most popular instruments which Copernicus used were quadrant, armilla, and triquetrum. All furnish some measure of the position of the heavenly body. It took an endless amount of mathematical calculations to come up with the Copernicus' theory. He had to find out how fast the Earth spins around the Sun, and how far the Sun is. He also had to calculate the length of the orbit of the Earth.