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 chal -
lenged a 2,000-year-old be lief that the earth sat motion less 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 develop ment 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
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 be lieved 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
measure ment 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 or bital 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.
Copernicus hoped to use “modern” (six teenth-century) technology to improve on Ptolemy’s measurements and, hope fully, eliminate some of the epi-circles.
For almost 20 years Copernicus pains takingly measured the position of the planets
each night. But his tables of findings still made no sense in Ptolemy’s model.
Over the years, Copernicus began to wonder what the movement of the planets would
look like from an other moving planet. When his calculations based on this idea more accurately predicted the planets’ actual movements, he began to wonder what the motion of the
planets would look like if the earth moved. Immediately, the logic of this notion became
Each planet appeared at different distances from the earth at different times through out
a year. Copernicus real ized that this meant Earth could not lie at the center of the planets’
From 20 years of observations he knew that only the sun did not vary in apparent size
over the course of a year. This meant that the distance from Earth to the sun had to always
remain the same. If the earth was not at the center, then the sun had to be. He quickly calculated that if he placed the sun at the universe’s center and had the earth or bit around it, he
could completely eliminate all epi-circles and have the known planets travel in simple circles around the sun.
But would any one believe Copernicus’s new model of the universe? The whole
world—and especially the all-powerful Catholic Church—be lieved in an Earth-centered
For fear of retribution from the Church, Copernicus dared not release his findings during his life time. They were made public in 1543, and even then they were consistently
scorned and ridiculed by the Church, astronomers, and universities alike. Finally, 60 years
later, first Johannes Kepler and then Galileo Galilei proved that Copernicus was right.
Fun Facts: Approximately one million Earths can fit in side the sun. But
that is slowly changing. Some 4.5 pounds of sun light hit the earth each