Born on February 19, 1473, in Torun, Poland, Nicolaus Copernicus was one of the most important people in the history of astronomy. After the death of his father, a wealthy merchant, he was sent to live with his uncle. His uncle sent him to the University of Krakow, which was famous for its philosophy, mathematics, and astronomy. After that he decided to study liberal arts at Bologna, medicine at Padua, and law at the University of Ferrara. Then he returned to Poland and settled at the cathedral in Frauenburg. His uncle helped him get elected a canon of the church. He also practiced medicine and studied a subject he had long been interested in: astronomy. The people before Copernicus thought there was a geocentric universe. A geocentric universe is where the earth is still at the center of several rotating spheres. Supposedly these held: the moon, Mercury, Venus, the sun, Mars, Jupiter, and Saturn. The outermost sphere held the so-called fixed stars. It was also said to wobble, producing equinoxes. These theories are called the cosmology theories. Yet there was one problem that troubled astronomers everywhere. This was the backward motion of Mars, Jupiter, and Saturn. Every now and then the motion of these planets seemed to halt. After that they proceed in the opposite direction. Astronomers tried to explain this backward motion. They believed that each planet revolved on the edge of a circle called the epicycle. The center of each epicycle revolved around the earth. Yet Copernicus didn't agree with these theories. He believed that the earth rotated daily on its axis and revolved around the sun. He also said the planets circle around the sun, and that the earth shakes as it rotates on its axis. The Copernican theory also kept some of the features of the cosmology it replaced. That included the planet-bearing spheres, and the outer most sphere with the fixed stars. Also Copernicus's theory also explained the daily and yearly motion of the sun and stars, and the backward motion of Mars, Jupiter, and Saturn.
Another feature of Copernicus's theory is the new order of the planets according to their periods of revolution. In his universe, the greater the planets orbit, the more time it takes to revolve around the sun. For most 16th century readers, accepting the Copernican theory was hard. They didn't like the idea of a moving earth. Parts of his theory were accepted, while other parts were rejected. Between 1543 and 1600 there were ten Copernicans. The most famous were Galileo and Johannes Kelper. During his life, Copernicus wrote five books. The first was a translation of letters by a 7th-century writer named Theophylace. Next he completed a short astronomical treatise, De Hypothesibus Motuum Coelestium a Se Constitutis. His third was Commentariolus, which told the principles of his theory of planetary movement. He wrote a treatise on money for his fourth. His fifth was De Revolutionibus Orbium Coelestium on the celestial spheres. This challenged the work of other astronomers. In 1588 a Danish astronomer named Tycho Brahe developed his own theory. In his theory the earth remains still as the sun rotates around it while all the other planets rotate around the sun. Many people accepted his geocentric-heliocentric system. By the late 17th century the Copernican theory became popular. Most major thinkers in England, France, the Netherlands, and Denmark were Copernicans. Philosophers in other European countries held strong anti-Copernican views. Overall, Nicolaus Copernicus influenced how we think about our solar system. That is because as we now know, his ideas were basically correct.