Tom Wernette Jr., age 15, of Danville, Ill., for his question:

WHAT IS THE COPERNICAN SYSTEM?

The Copernican system is an important part of astronomy. It is a systematic explanation of the movement of the planets around the sun. The system was described in 1543 by the great Polish astronomer Nicolaus Copernicus.

The Copernican system advanced the theories that the earth and the planets are all revolving in orbits around the sun, and that the earth is spinning on its north south axis from west to east at a rate of one rotation per day.

These two hypotheses supersede the Ptolemaic system which had been the basis of astronomical theory until that time. The Copernican system first described the precession of the equinoxes but did not explain the mechanical action that caused it.

Publication of the Copernican system stimulated the study of astronomy and mathematics and laid the basis for the discoveries of the German astronomer Johannes Kepler and the British astronomer Sir Isaac Newton.