Nicolaus Copernicus, who lived from 1473 until 1543, is known for his idea that the sun is motionless at the center of the universe and that the earth and other planets all revolve around it. This Polish astronomer revolutionized beliefs involving the universe, making his thoughts controversial in his time, but common knowledge in our own (Westman).
Before the time of Copernicus, people had extremely different views of the universe. A Greek astronomer named Ptolemy had his own theory of the earth and its relationship with the sun and other planets. Around 140 AD, he came up with a system that showed the earth at the center of the universe with the sun and planets revolving around it in a spherical shape (Reichenbach 15-17). Ptolemy also believed that the earth remained still and that the outermost sphere contained the stars, which were fixed in space (Westman).
Copernicus's theory showed the earth and other planets revolving around the sun in a circular motion. At the same time, the moon is rotating around the earth as well. Like Ptolemy, Copernicus believed that the stars occupied the region farthest from the sun. Copernicus, however, never stated whether or not these stars were in a fixed sphere around the universe or if they were scattered throughout space. Unlike Ptolemy's motionless earth, Copernicus said the earth rotates around itself daily, causing night and day (Armitage, 112-15). He also realized that the greater the distance from the sun a planet was, the more time it takes for that planet to completely revolve around the sun (Westman).
At first, Copernicus only planned to use his new system as an easier way to chart the planets' positions. But, he explained everything with such high detail and mathematics that astronomers around the time of his death began to wonder if his theory might actually be the truth. He was cautious to publish his ideas because he saw potential for trouble and possibly even a heresy charge...