Astronomers, scientists who study the universe, have technology and centuries of science to back up theories about space. Modern science has taken us to places ancient astronomers could only dream of.

But the knowledge passed down through centuries wasn't always accurate. Until the middle of the 16th century, most astronomers believed that the Earth was fixed in space and everything in the heavens revolved around it.

Nicolaus Copernicus, born in 1473 in Poland, was the second person to advance the theory contradicting that commonly held belief. Without instruments, Copernicus used mathematics to formulate his theory that the sun is the center. An ancient Greek astronomer, Aristarchus, held a similar belief, but his ideas were discounted.

In 1530, Copernicus wrote his theories in a work titled "De Revolutionibus" that explains that the Earth rotated once every 24 hours and traveled around the sun once a year.

By the early 1600s, Galileo and Johannes Kepler began to develop the physics that would prove Copernicus' theories.

Today, Copernicus is considered the founder of modern astronomy. In honor of his birthday Feb. 19, I made a model of the planet Saturn using directions from http://spaceplace.jpl.nasa.gov on the Web.

Supplies you will need:

• 1 old compact disc.

• 1 2-inch foam ball.

• White glue.

• Paint brush.

• Glitter.

• Paper clip.

• Toothpicks.

Ask an adult to cut the foam ball in half. Spread newspapers on your work surface.

On the side of the CD that has writing, spread a ring of glue around the outside edge using a paint brush.

Sprinkle glitter on the ring and let dry completely. Shake off excess glitter.

Continue making rings (vary the width of each) with different colors of glitter, allowing each one to dry before starting the next. Do not cover the center of the CD.

Put a toothpick into the flat side of each half of the foam ball. Cover each with glue and sprinkle with glitter. Set aside to dry.

Spread glue around the center on both sides of the CD. Put the half balls on either side, flat sides together. Clip off the toothpicks if they protrude through the foam.

Bend a paper clip until it's straight. Leave one end looped. Push it through both sides of the ball on the ring side of the CD. Place it about one-half inch from the center of the ball, so the planet appears to be on its axis. Use thread or yarn to hang.