Unit 3
The Solar System

The solar system has been studied by human beings since the beginning of historical time. Observations of the motions of the planets, made first by the Babylonians and then by the Greeks, led to the development of the first cosmological models. Later refinement and analysis of these observations led Kepler, and eventually Newton, to an understanding of fundamental physical laws.

Although we have observed the bodies of the solar system for many centuries, first with the naked eye and later with the telescope, we have discovered more about the properties of these bodies in the last thirty years than in all the preceding centuries. This dramatic increase in available information results, of course, from space probes, several of which have landed on a planet’s surface. The high resolution photographs taken by probes allow a close-up view that is much better than that obtained from Earth.