Birthday of Copernicus

Today is the anniversary of the birth of the Polish astronomer Nicolaus Copernicus (1473-1543).  His Polish name is Mikołaj Kopernik.  His greatest work was De revolutionibus orbium coelestium.   In this he described the heliocentric, or sun centered, solar system.  At the time this was seen as revolutionary since the Catholic Church taught that the earth was the center of the universe.  Yet he observed movements of the sun and planets that could not be explained if the sun revolved around the earth.  So the earth and other planets had to revolve around the sun.  We have now come to accept this, though we know that the orbits of the planets are elliptical, rather than circular, with the sun at one of the focal points of the ellipse.