Saturn's Moons

It took millennia between the time the first astronomers understood the relationship between the stars and the seasons, and the European renaissance when scientists like Copernicus, Galileo, Kepler, and Newton developed our modern theory for the solar systems. During that time, many theories were developed to describe the motions of the moon, sun and stars. In the 3rd century B.C., the Greek astronomer Aristarcus of Samos actually used geometric arguments to develop a model for the solar system much like the modern one, in which the earth and the other planets revolved around the sun, and the moon around the earth. Nonetheless, in Europe and the Middle East, the arguments of Plato and Aristotle (from the 5th century B.C.), eventually won out, and persisted for two thousand years. Ptolemy (2nd century A.D.) synthesized the work of generations of sky-watchers that followed, and developed a mathematical model in which the sun, moon, and planets orbited the earth on a series of spheres. This model proved accurate enough to be used for over 1000 years.

Scientific thought eventually changed because of two developments. First, the idea that the Earth was the center of the universe was called into question by Copernicus, and was dealt a death-blow when Galileo pointed his telescope at Jupiter and saw that it was orbited by several moons. The above image shows a modern photograph of the limb of Saturn taken by the Cassini spacecraft, along with its orbiting dust ring and two of its moons.

The other development was the mathematical model of Kepler, which placed the Sun at the center of the solar system, and supposed that the planets followed ellipses around the Sun. This model was both simpler and more accurate than the epicycles of Ptolemy's model. Moreover, Newton eventually developed a mathematical model for gravity that naturally explained the elliptical motions of all of the planets and their moons. With that, the modern age of mathematical physics began.