Copernican

by Jerry Coffey on March 22, 2010

heliocentric model

The Copernican system in astronomy is used to refer to the work and theories of Nicolaus Copernicus. His greatest contribution to history is his theory of heliocentrism. Heliocentric theories had been proposed prior to his body of work, but had been dismissed for various reasons. The main reason was that it was hard to convince anyone, from common man to king, that the Earth was anything other than the center of all things that existed. That geocentric belief system held sway over the educated and ignorant, alike for thousands of years.

The heliocentric theory of Copernicus was first published in 1543, shortly before his death. It is often thought of as the single most important idea that jump started the Scientific Revolution and helped to bring about an end to the Middle Ages. This model, with the sun at the center of the universe, demonstrated that the observed motions of celestial objects can be explained without putting the Earth at rest in the center of the universe. Several ancient astronomers had proposed similar ideas: Philolaus in the 4th century B.C and Aristarchus in the 3rd century B.C, along with several Muslim astronomers in the 14th and 15 centuries A.D. The early theories of Aristarchus and Philolaus have not survived for study, but Copernicus cited them in his early bodies of work.

When Copernicus first introduced his theory, it had to compete against the geocentic theory of Ptolemy. That theory had been widely accepted since its introduction in the year 150 A.D. The Ptolemaic system drew on many previous theories that viewed Earth as a stationary center of the universe. Stars were embedded in a large outer sphere which rotated relatively rapidly, while the planets dwelt in smaller spheres —a separate one for each planet. To account for apparent anomalies in this view, such as the apparent retrograde motion of the planets, a system of deferents and epicycles was used. The planet was said to revolve in a small circle (the epicycle) about a center, which itself revolved in a larger circle (the deferent) about a center on or near the Earth.

Copernicus held that the Earth is another planet revolving around the fixed sun once a year, and turning on its axis once a day. While Copernicus put the Sun at the center of the celestial spheres, he did not put it at the exact center of the universe. Near it, but not dead on. Copernicus’ system used only uniform circular motions, correcting what was seen by many as the chief inelegance in Ptolemy’s system. He added another motion to the Earth, by which the axis is kept pointed throughout the year at the same place in the heavens; it has been recognized that for the Earth not to point to the same place would have been a motion.

There are six major points to the Copernican system:

Heavenly motions are uniform, eternal, and circular or compounded of several circles (epicycles).

The center of the universe is near the Sun

Around the Sun, in order, are Mercury, Venus, Earth and Moon, Mars, Jupiter, Saturn, and the fixed stars.

The Earth has three motions: daily rotation, annual revolution, and annual tilting of its axis.

Retrograde motion of the planets is explained by the Earth’s motion.

The distance from the Earth to the sun is small compared to the distance to the stars.

Copernicus found no following for his beliefs during his lifetime and very little support for it surfaced for a hundred years after his death. Even modern astronomers vary on their opinion of his overall contributions to the science. However you feel about the total effect of the astronomer, his theories were revolutionary to say the least.

Here is a good article about Nicolaus Copernicus. We have a great article about heliocentism here on Universe Today. Astronomy Cast offers a good episode about the center of the universe.