The Sun Is the Center
of the Universe
Year of Discovery: A.D. 1520
What Is It? The sun is the center of the universe and the earth rotates around it.
Who Discovered It? Nicholaus Copernicus
Why Is This One of the 100 Greatest?
Copernicus measured and observed the planets and stars. He gathered, compiled, and
compared the observations of dozens of other astronomers. In so doing Copernicus challenged a 2,000-year-old belief that the earth sat motionless at the center of the universe and
that planets, sun, and stars rotated around it. His work represents the beginning point for our
understanding of the universe around us and of modern astronomy.
He was also the first to use scientific observation as the basis for the development of a
scientific theory. (Before his time logic and thought had been the basis for theory.) In this
way Copernicus launched both the field of modern astronomy and modern scientific
methods.
How Was It Discovered?
In 1499 Copernicus graduated from the University of Bologna, Italy; was ordained a
priest in the Catholic Church; and returned to Poland to work for his uncle, Bishop
Waczenrode, at the Frauenburg Cathedral. Copernicus was given the top rooms in a cathedral tower so he could continue his astronomy measurements.
At that time people still believed a model of the universe created by the Greek scientist,
Ptolemy, more than 1,500 years earlier. According to Ptolemy, the earth was the center of
the universe and never moved. The sun and planets revolved around the earth in great circles, while the distant stars perched way out on the great spherical shell of space. But careful
measurement of the movement of planets didn’t fit with Ptolomy’s model.
So astronomers modified Ptolemy’s universe of circles by adding more circles within
circles, or epi-circles. The model now claimed that each planet traveled along a small circle
(epi-circle) that rolled along that planet’s big orbital circle around the earth. Century after
century, the errors in even this model grew more and more evident. More epi-circles were
added to the model so that planets moved along epi-circles within epi-circles.
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